394 engine has small miss - need advice
January 6th, 2014, 05:37 PM
#1
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394 engine has small miss - need advice
Hello, I have a 1964 98 with a 394 Rocket engine.
The body of the car was being restored and I had the engine out for about a year. The engine worked perfectly fine before removing it without any miss. Since then, I have replaced the water pump, intake manifold gasket, carburator gasket, and the distributor gasket.
I have not made any changes to the carburator settings
I had made a small mark on the distributor base and the block prior to removing it and put it back in the same position and align the distributor cap with #1 piston TDC. The miss is accompanied by a very faint pop which can be heard from the exhaust pipe.
I have checked compression on all 8 cylinders and the numbers i got are 155, 150, 165, 160 (Driver) 145, 160, 145, 145 (Passenger) with engine cold
1. Are the numbers above normal, or should i be concerned about the 145s?
2. The distributor has the Petroix ignition which replaces the points, I have bought a timing gun, but I have never set the timing on a motor that uses a distributor.
Does anyone know the procedure for setting the correct timing on a 394? The timing gun I have does not have an RPM reader, not sure on how relevant that is.
Any help would be greatly appreciated.
The body of the car was being restored and I had the engine out for about a year. The engine worked perfectly fine before removing it without any miss. Since then, I have replaced the water pump, intake manifold gasket, carburator gasket, and the distributor gasket.
I have not made any changes to the carburator settings
I had made a small mark on the distributor base and the block prior to removing it and put it back in the same position and align the distributor cap with #1 piston TDC. The miss is accompanied by a very faint pop which can be heard from the exhaust pipe.
I have checked compression on all 8 cylinders and the numbers i got are 155, 150, 165, 160 (Driver) 145, 160, 145, 145 (Passenger) with engine cold
1. Are the numbers above normal, or should i be concerned about the 145s?
2. The distributor has the Petroix ignition which replaces the points, I have bought a timing gun, but I have never set the timing on a motor that uses a distributor.
Does anyone know the procedure for setting the correct timing on a 394? The timing gun I have does not have an RPM reader, not sure on how relevant that is.
Any help would be greatly appreciated.
January 7th, 2014, 06:58 AM
#2
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Join Date: Apr 2010
Posts: 978
Help
First thing I would do is try to isolate the cylinder you have the misfire coming from. Then you will need to determine if it is mechanical or secondary ignition. I don't think you have a mechanical issue because your compression test looks pretty good. 145 PSI is still OK for compression. I believe the rule of thumb about compression variance is: the manufacturer does not want more than 10% difference. The best way to isolate the problem cylinder is to remove the ignition wires one at a time, with insolated ignition wire pliers, with the engine running. The RPM should drop from each wire. If you get to one that makes no change that is your problem cylinder. After you figure out which cylinder is causing the misfire you can swap an ignition wire or spark plug to a different cylinder to see if the misfire moves. Only change one thing at a time. If the misfire does not move to the other cylinder remove the distributor cap to see if there is excessive corrosion on that cylinder terminal under the cap. If there is, you can try to scrape it away or replace the cap and rotor. I don't think you have a carb problem because generally it would not be just one cylinder misfiring. There is a possibility you may have a vacuum leak causing the misfire but that is unlikely since you just changed the intake gasket. You could spray around with carb clean to see if the engine smooths out, but if you have just painted everything nice and pretty, you could use a propane torch, unlit, for the same results.
I have a '64 Dynamic 88 that I picked up a while back that had a ticking noise coming from under one of the valve covers. Turned out to be two bad rocker arms. The pushrods had worn into the cups. As far as setting the timing, I do have the service manual on disk that I could share information with you from, but I think with the Petronics electronic ignition the timing should be set different than the factory spec, when using points. My friend Dane Luling from Mild to Wild Racing is a Petronics dealer. I will contact him later today to see what he has to say about your timing spec. I hope this helps.
I have a '64 Dynamic 88 that I picked up a while back that had a ticking noise coming from under one of the valve covers. Turned out to be two bad rocker arms. The pushrods had worn into the cups. As far as setting the timing, I do have the service manual on disk that I could share information with you from, but I think with the Petronics electronic ignition the timing should be set different than the factory spec, when using points. My friend Dane Luling from Mild to Wild Racing is a Petronics dealer. I will contact him later today to see what he has to say about your timing spec. I hope this helps.
January 7th, 2014, 09:12 AM
#3
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Thank you for your reply.
I like the idea of testing each plug and wire individually, I was tempted to do that but someone had told me there is a lot of electricity flowing through those wires. I will stop by the auto parts store to get one of those special pliers you mentioned.
You know when I started the engine after a year, I did have a bit of a tapping noise, I added 1 quart of tranny fluid to the oil and the tapping is almost completely gone. It was coming from the rocker arms cover area, which made me believe it was a stuck or dirty lifter. I think in my case the issue maybe ignition as you pointed out.
By curiosity was your car having a slight misfire due to the worn rocker arms and pushrods? I am tempted to remove the rocker arm covers and maybe run the engine with the cover open just to make sure it all looks ok. Do you know if it would be quite messy because of oil going all over the place? have u ever done that in the past?
Thanks for all your help
I like the idea of testing each plug and wire individually, I was tempted to do that but someone had told me there is a lot of electricity flowing through those wires. I will stop by the auto parts store to get one of those special pliers you mentioned.
You know when I started the engine after a year, I did have a bit of a tapping noise, I added 1 quart of tranny fluid to the oil and the tapping is almost completely gone. It was coming from the rocker arms cover area, which made me believe it was a stuck or dirty lifter. I think in my case the issue maybe ignition as you pointed out.
By curiosity was your car having a slight misfire due to the worn rocker arms and pushrods? I am tempted to remove the rocker arm covers and maybe run the engine with the cover open just to make sure it all looks ok. Do you know if it would be quite messy because of oil going all over the place? have u ever done that in the past?
Thanks for all your help
January 7th, 2014, 09:46 AM
#4
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Join Date: Apr 2010
Posts: 978
misfire
Thank you for your reply.
I like the idea of testing each plug and wire individually, I was tempted to do that but someone had told me there is a lot of electricity flowing through those wires. I will stop by the auto parts store to get one of those special pliers you mentioned.
You know when I started the engine after a year, I did have a bit of a tapping noise, I added 1 quart of tranny fluid to the oil and the tapping is almost completely gone. It was coming from the rocker arms cover area, which made me believe it was a stuck or dirty lifter. I think in my case the issue maybe ignition as you pointed out.
By curiosity was your car having a slight misfire due to the worn rocker arms and pushrods? I am tempted to remove the rocker arm covers and maybe run the engine with the cover open just to make sure it all looks ok. Do you know if it would be quite messy because of oil going all over the place? have u ever done that in the past?
Thanks for all your help
I like the idea of testing each plug and wire individually, I was tempted to do that but someone had told me there is a lot of electricity flowing through those wires. I will stop by the auto parts store to get one of those special pliers you mentioned.
You know when I started the engine after a year, I did have a bit of a tapping noise, I added 1 quart of tranny fluid to the oil and the tapping is almost completely gone. It was coming from the rocker arms cover area, which made me believe it was a stuck or dirty lifter. I think in my case the issue maybe ignition as you pointed out.
By curiosity was your car having a slight misfire due to the worn rocker arms and pushrods? I am tempted to remove the rocker arm covers and maybe run the engine with the cover open just to make sure it all looks ok. Do you know if it would be quite messy because of oil going all over the place? have u ever done that in the past?
Thanks for all your help
First of all be careful about the pliers you purchase. I had some that did not insulate well at all, it was a shocking experience. If you're frugal you can wrap the head of regular pliers with electrical tape and wear a rubber glove. It also helps if you loosen each ignition wire with the engine off, then just barely put them back on. Don't clip them all the way onto the plug. This will not cause a misfire. Don't stand in a puddle of water or ground yourself to the car.
As far as trans fluid in the oil, I have never tried that. I generally don't like to thin out the oil. I have had good luck using Sea Foam to free up sticky lifters. I poor in the entire can and hold the RPM up at 2000 for 5 minutes, than do a regular oil change right away.
The car I picked up had sat in a barn on a trailer for fifteen years. It needed a bit of work to make it street-able. It did seem to have a bit of a misfire with the bad rockers. These engines don't send oil to the heads through the push rod, but through passages in the block up to the rocker shaft and across. If you do find a problem rocker, be careful when removing and reinstalling the shaft mount pedestals. Each one has a head bolt as well as a shorter bolt. Always torque to spec. These engines use a metal tin type head gasket that should not be disturbed. I developed a blown head gasket after my repair. I have the heads off right now doing a valve job to them.
I ran my engine with the valve covers off and it is kind of messy. Put a wide pan or a couple cookie sheets underneath. You can always clean the engine compartment afterward with brake clean and compressed air. If I would have looked before running my engine I would have seen the bad rockers. Just grab each one and see if there is a lot of play. As long as the rocker isn't pushing a valve open it's easy to spot.
115-1513_IMG.jpg
January 7th, 2014, 10:10 AM
#5
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Could you describe the "small miss" a bit more? Does it occur in a regular rythym or does it vary? Can you feel or hear a popping at the exhaust pipe? Does it occur all the time thru different rev ranges or is it only at idle? A regular miss thru all rev ranges would indicate a single misfiring cylinder while an irregular miss at idle only could indicate a vacuum leak or carburetor issue. Checking cap, rotor, and plug wires is good, also pull the plugs and check the gap and cleanliness if they are not new. "Reading" the plugs might help as a regular misfire might show up as a carbon fouled plug. I will say from personal experience that vacuum leaks can be a major cause of uneven running - check by removing and plugging each vacuum line attached to the engine individually and see if the miss goes away. I had one major leak at the distributor vacuum advance diaphragm that caused an uneven idle. Good luck!
January 7th, 2014, 10:40 AM
#6
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Join Date: Dec 2013
Posts: 180
Both Don and Cutlass Freak have given good tips here! 
One other thing you can try is to warm the engine, bring to curb idle, and cup your hand over the top of the carb, as if to "choke" it. This sometimes will reveal if you have a lean condition causing the miss, as the engine will speed up slightly when choked. This could tell you if you have a vacuum leak at the manifold, or carb, or possibly a hose off somewhere.
I suspect you may have a spark plug fouled, or dislodged some carbon when changing the manifold gasket, and the removal of spark plug wires on at a time should show you which one it is........but be prepared to get knocked on your a$$ if you're not careful.....lol!
Have you run this engine out on the highway since the work was done? Engines don't like to sit idle; I would replace the spark plugs, if you did not do so during the compression test. By the way, your compression on a cold engine sounds ok, especially if it has not been exercised recently!
Let us know what you find!
One other thing you can try is to warm the engine, bring to curb idle, and cup your hand over the top of the carb, as if to "choke" it. This sometimes will reveal if you have a lean condition causing the miss, as the engine will speed up slightly when choked. This could tell you if you have a vacuum leak at the manifold, or carb, or possibly a hose off somewhere.
I suspect you may have a spark plug fouled, or dislodged some carbon when changing the manifold gasket, and the removal of spark plug wires on at a time should show you which one it is........but be prepared to get knocked on your a$$ if you're not careful.....lol!
Have you run this engine out on the highway since the work was done? Engines don't like to sit idle; I would replace the spark plugs, if you did not do so during the compression test. By the way, your compression on a cold engine sounds ok, especially if it has not been exercised recently!
Let us know what you find!
January 7th, 2014, 12:45 PM
#7
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Join Date: Aug 2011
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Double check the firing order using the sequence stamped on the intake manifold and check it again.
Ignition related cylinder misfires can often be located using an inductive pick up timing light. With the engine running put the inductive pick up on each wire one at a time, aim the light at the hood or firewall do not stare into the flashing light and look for an accompanying skip in the light flash the same time as the misfire. If the light pattern interrupts at the same time or frequency as the miss on any cylinder the problem is on that cylinder.
If you do not have an inductive pick up light you will have to turn the car off each time before changing cylinders to prevent be severely shocked.
Keep us posted on what you find and good luck!
Ignition related cylinder misfires can often be located using an inductive pick up timing light. With the engine running put the inductive pick up on each wire one at a time, aim the light at the hood or firewall do not stare into the flashing light and look for an accompanying skip in the light flash the same time as the misfire. If the light pattern interrupts at the same time or frequency as the miss on any cylinder the problem is on that cylinder.
If you do not have an inductive pick up light you will have to turn the car off each time before changing cylinders to prevent be severely shocked.
Keep us posted on what you find and good luck!
January 7th, 2014, 01:48 PM
#8
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I would freshen up my tune by pulling all the plugs, inspect and regap. Inspect the spark plug wires, cap, and rotor, replace as required. Then set the timing to 5-7.5 degrees BTDC @ 550-600 rpm, which is what I think it calls for. Then adjust the carb with a vacuum gauge or tach for the highest vacuum or rpm depending on which method you use. And reset idle idle speed back to 550-600. Also make sure your choke is operating correctly.
January 7th, 2014, 02:06 PM
#9
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Posts: 978
Good advice
I would freshen up my tune by pulling all the plugs, inspect and regap. Inspect the spark plug wires, cap, and rotor, replace as required. Then set the timing to 5-7.5 degrees BTDC @ 550-600 rpm, which is what I think it calls for. Then adjust the carb with a vacuum gauge or tach for the highest vacuum or rpm depending on which method you use. And reset idle idle speed back to 550-600. Also make sure your choke is operating correctly.
When in doubt replace with known good part. I have the service manual for this model, but I was reluctant to post timing specs because there is four different possibilities depending on what distributor is being used. Also I'm not sure but I believe Petronics recommends entirely different specs from stock. The plug gap is also different.
January 7th, 2014, 02:38 PM
#11
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Stock settings
OK well here's one of the four options:
Series 31,32,33,34
High compression 2BBL/ 4 BBL
Dist # 1111048 vacuum unit 1116232
Based on distributor RPM
Vacuum advance per inch of vacuum
Start - 6 to 8 In. Hg.
7 1/2* to 10* @ 18 In. Hg.
Mechanical advance per distributor RPM
0*-2* @ 400RPM
7 1/2*-9 1/2* @ 1000RPM
12*-14* @ 2100RPM
Hope this helps but will probably just confuse most
Series 31,32,33,34
High compression 2BBL/ 4 BBL
Dist # 1111048 vacuum unit 1116232
Based on distributor RPM
Vacuum advance per inch of vacuum
Start - 6 to 8 In. Hg.
7 1/2* to 10* @ 18 In. Hg.
Mechanical advance per distributor RPM
0*-2* @ 400RPM
7 1/2*-9 1/2* @ 1000RPM
12*-14* @ 2100RPM
Hope this helps but will probably just confuse most
January 7th, 2014, 02:53 PM
#12
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Location: Big Lake,MN..Spent most of my life in Boston
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Hey 67 Cutlass Freak...great looking car. Great color and great style. I have a 64 dynamic. I read the 394 had small oil drain holes that are famous for getting plugged. When I removed valve covers to replace gaskets I used pipe cleaners soaked in tranny fluid and cleared them. I found on a GM web site that these oil drain lines are a major cause for engine failure...any thoughts.
January 7th, 2014, 03:03 PM
#13
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Posts: 978
Thoughts
Hey 67 Cutlass Freak...great looking car. Great color and great style. I have a 64 dynamic. I read the 394 had small oil drain holes that are famous for getting plugged. When I removed valve covers to replace gaskets I used pipe cleaners soaked in tranny fluid and cleared them. I found on a GM web site that these oil drain lines are a major cause for engine failure...any thoughts.
This is true, even for the more modern Olds V-8 engines. The oil passages tend to get clogged up from poor maintenance (sludge), or from sitting (rust). It usually occurs more on the passenger side head on the 394 from sitting because of the breather. Moisture tends to get in there easier. Look at the crap that was under my valve covers-
113-1395_IMG.jpg
January 8th, 2014, 10:29 AM
#14
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Location: Big Lake,MN..Spent most of my life in Boston
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Just about what mine looked like. I changed oil three or four times within 1000 miles after cleaning drains and replacing gaskets.Would be curious to see what it looks like now but I will await until I need to change gaskets again. I am curious about the #23 on block. I have a number also. What does it mean?
January 8th, 2014, 11:50 AM
#15
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Posts: 75
Hello All,
I really appreciate all the advice. I am planning on performing all the procedures you guys have suggested. I got a timing light and the spark plug pliers. I have ordered a dwell and Tach meter as the timing gun I have does not have a Tach.
Thank you all, I will keep you all posted.
On regards on getting more details about the miss. I will try to do that today after work and see if it happens in all of the RPM range. The car is not drivable yet as the transmission is off. I am replacing the damper plate this weekend.
I really appreciate all the advice. I am planning on performing all the procedures you guys have suggested. I got a timing light and the spark plug pliers. I have ordered a dwell and Tach meter as the timing gun I have does not have a Tach.
Thank you all, I will keep you all posted.
On regards on getting more details about the miss. I will try to do that today after work and see if it happens in all of the RPM range. The car is not drivable yet as the transmission is off. I am replacing the damper plate this weekend.
January 13th, 2014, 11:57 AM
#18
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Hello All,
Not so good news, this is what I did this weekend and what I am seeing:
1. I connected my timing gun to the distributor #1 cable and set the timing at 8 degrees BTDC (with the vacuum advance disconnected from the distributor). Once I connect the advance, it reads 38 degrees
2. I connected the timing gun to each individual spark plug cable to determine which cylinder was missing and try to observe any break on the light coming out. They all checked OK.
3. I run the engine in idle and started pulling each spark plug cable one at a time to see which one would be the one that does not make a change on idle. I found that pulling the cable from all cylinders except cylinder #6 made the idle worse.
4. I then decided to swap out the plug from #6 with another cylinder and it still miss on #6 (once again pulling the spark plug cable while engine running made no difference)
5. I then decided to swap out the cables from #6 with another cylinder and it still miss on #6 (once again pulling the spark plug cable while engine running made no difference)
6. Then I decided to change the rotor cap and rotor (though the timing light indicated all cylinders were getting current from the distributor). Re-tested and still miss on #6 (once again pulling the spark plug cable while engine running made no difference)
Cylinder #6 is the one I found to have the lowest compression which was slightly higher than 140 (see my numbers on top of thread). I have other cylinders reading around 145, 150 and even 160. The service manual says that up to 20% difference is ok. In any case 140 is not that bad.
What I noticed is that the spark plug that I pulled from #6 looked as if it had not been firing and had a slight shine on it, as if it had a very thin coat of oil. However, even when I swapped that plug out, the miss remained on #6.
Could it be that there is spark going to that cylinder but that is not strong enough?
Do you guys think that the plug is firing, but that there is something mechanically wrong and that the plug is in fact firing?
I have the petronix ignitor replacement for points installed in the distributor and I wonder if somehow the gap between the ignitor and the rotating plate is wider around cylinder #6 firing point and I am getting weak spark.
I wonder if the issue is worn rings and that I need to rebuild? or maybe user a thicker oil to get by.
Guys any help would be great, I really want to get this resolved at a minimum cost if possible (not sure if that is feasible). Got a baby on the way and engine rebuild is out of the equation.
Not so good news, this is what I did this weekend and what I am seeing:
1. I connected my timing gun to the distributor #1 cable and set the timing at 8 degrees BTDC (with the vacuum advance disconnected from the distributor). Once I connect the advance, it reads 38 degrees
2. I connected the timing gun to each individual spark plug cable to determine which cylinder was missing and try to observe any break on the light coming out. They all checked OK.
3. I run the engine in idle and started pulling each spark plug cable one at a time to see which one would be the one that does not make a change on idle. I found that pulling the cable from all cylinders except cylinder #6 made the idle worse.
4. I then decided to swap out the plug from #6 with another cylinder and it still miss on #6 (once again pulling the spark plug cable while engine running made no difference)
5. I then decided to swap out the cables from #6 with another cylinder and it still miss on #6 (once again pulling the spark plug cable while engine running made no difference)
6. Then I decided to change the rotor cap and rotor (though the timing light indicated all cylinders were getting current from the distributor). Re-tested and still miss on #6 (once again pulling the spark plug cable while engine running made no difference)
Cylinder #6 is the one I found to have the lowest compression which was slightly higher than 140 (see my numbers on top of thread). I have other cylinders reading around 145, 150 and even 160. The service manual says that up to 20% difference is ok. In any case 140 is not that bad.
What I noticed is that the spark plug that I pulled from #6 looked as if it had not been firing and had a slight shine on it, as if it had a very thin coat of oil. However, even when I swapped that plug out, the miss remained on #6.
Could it be that there is spark going to that cylinder but that is not strong enough?
Do you guys think that the plug is firing, but that there is something mechanically wrong and that the plug is in fact firing?
I have the petronix ignitor replacement for points installed in the distributor and I wonder if somehow the gap between the ignitor and the rotating plate is wider around cylinder #6 firing point and I am getting weak spark.
I wonder if the issue is worn rings and that I need to rebuild? or maybe user a thicker oil to get by.
Guys any help would be great, I really want to get this resolved at a minimum cost if possible (not sure if that is feasible). Got a baby on the way and engine rebuild is out of the equation.
January 13th, 2014, 12:07 PM
#19
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Location: Poteau, Ok
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Are you sure that connecting the vacuum advance back is sending your timing to 38? Have you tried replacing just the number 6 wire? Your compression in the cylinders is ok, and well within the level of an acceptable difference from the others.
January 13th, 2014, 12:45 PM
#20
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Join Date: Apr 2010
Posts: 978
Sounds to me like you have covered the bases on ignition. I believe you have a problem with the advance going up to 38 degrees with the vacuum plugged in, but that is not causing your misfire. I would recomend pulling the valve cover. It sounds like you have a mechanical problem. Remove the coil wire and have a friend crank over the engine. Watch to see if both valves are opening on cylinder number six. I'm betting you have a rocker or lifter problem. This would not show up on a compression test that well because if both vaves are closed you would still have compression.
January 13th, 2014, 02:11 PM
#22
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Join Date: Apr 2010
Posts: 978
Next step
Hello All,
Not so good news, this is what I did this weekend and what I am seeing:
1. I connected my timing gun to the distributor #1 cable and set the timing at 8 degrees BTDC (with the vacuum advance disconnected from the distributor). Once I connect the advance, it reads 38 degrees
2. I connected the timing gun to each individual spark plug cable to determine which cylinder was missing and try to observe any break on the light coming out. They all checked OK.
3. I run the engine in idle and started pulling each spark plug cable one at a time to see which one would be the one that does not make a change on idle. I found that pulling the cable from all cylinders except cylinder #6 made the idle worse.
4. I then decided to swap out the plug from #6 with another cylinder and it still miss on #6 (once again pulling the spark plug cable while engine running made no difference)
5. I then decided to swap out the cables from #6 with another cylinder and it still miss on #6 (once again pulling the spark plug cable while engine running made no difference)
6. Then I decided to change the rotor cap and rotor (though the timing light indicated all cylinders were getting current from the distributor). Re-tested and still miss on #6 (once again pulling the spark plug cable while engine running made no difference)
Cylinder #6 is the one I found to have the lowest compression which was slightly higher than 140 (see my numbers on top of thread). I have other cylinders reading around 145, 150 and even 160. The service manual says that up to 20% difference is ok. In any case 140 is not that bad.
What I noticed is that the spark plug that I pulled from #6 looked as if it had not been firing and had a slight shine on it, as if it had a very thin coat of oil. However, even when I swapped that plug out, the miss remained on #6.
Could it be that there is spark going to that cylinder but that is not strong enough?
Do you guys think that the plug is firing, but that there is something mechanically wrong and that the plug is in fact firing?
I have the petronix ignitor replacement for points installed in the distributor and I wonder if somehow the gap between the ignitor and the rotating plate is wider around cylinder #6 firing point and I am getting weak spark.
I wonder if the issue is worn rings and that I need to rebuild? or maybe user a thicker oil to get by.
Guys any help would be great, I really want to get this resolved at a minimum cost if possible (not sure if that is feasible). Got a baby on the way and engine rebuild is out of the equation.
Not so good news, this is what I did this weekend and what I am seeing:
1. I connected my timing gun to the distributor #1 cable and set the timing at 8 degrees BTDC (with the vacuum advance disconnected from the distributor). Once I connect the advance, it reads 38 degrees
2. I connected the timing gun to each individual spark plug cable to determine which cylinder was missing and try to observe any break on the light coming out. They all checked OK.
3. I run the engine in idle and started pulling each spark plug cable one at a time to see which one would be the one that does not make a change on idle. I found that pulling the cable from all cylinders except cylinder #6 made the idle worse.
4. I then decided to swap out the plug from #6 with another cylinder and it still miss on #6 (once again pulling the spark plug cable while engine running made no difference)
5. I then decided to swap out the cables from #6 with another cylinder and it still miss on #6 (once again pulling the spark plug cable while engine running made no difference)
6. Then I decided to change the rotor cap and rotor (though the timing light indicated all cylinders were getting current from the distributor). Re-tested and still miss on #6 (once again pulling the spark plug cable while engine running made no difference)
Cylinder #6 is the one I found to have the lowest compression which was slightly higher than 140 (see my numbers on top of thread). I have other cylinders reading around 145, 150 and even 160. The service manual says that up to 20% difference is ok. In any case 140 is not that bad.
What I noticed is that the spark plug that I pulled from #6 looked as if it had not been firing and had a slight shine on it, as if it had a very thin coat of oil. However, even when I swapped that plug out, the miss remained on #6.
Could it be that there is spark going to that cylinder but that is not strong enough?
Do you guys think that the plug is firing, but that there is something mechanically wrong and that the plug is in fact firing?
I have the petronix ignitor replacement for points installed in the distributor and I wonder if somehow the gap between the ignitor and the rotating plate is wider around cylinder #6 firing point and I am getting weak spark.
I wonder if the issue is worn rings and that I need to rebuild? or maybe user a thicker oil to get by.
Guys any help would be great, I really want to get this resolved at a minimum cost if possible (not sure if that is feasible). Got a baby on the way and engine rebuild is out of the equation.
January 13th, 2014, 03:14 PM
#24
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Join Date: Aug 2011
Posts: 2,999
Compression numbers sound fine. Did you re-check the firing order as stamped on the manifold?
Can you pull the carburetor and look for restrictions/clogs in the intake runner to #6? Perhaps that cylinder is not getting fuel since you have spark and compression.
Disconnect the coil, pull the valve cover, crank the engine and watch the valve action on that cylinder to see if both valves open and close fully.
38 degrees at idle sounds like full unported intake vacuum is going to the advance. Ported vacuum would come off the carburetor from above the throttle plates and be applied as the throttle plates open. Can someone chime in to advise if there should be ported or unported vacuum on this application '64 98 with a 394?
Can you pull the carburetor and look for restrictions/clogs in the intake runner to #6? Perhaps that cylinder is not getting fuel since you have spark and compression.
Disconnect the coil, pull the valve cover, crank the engine and watch the valve action on that cylinder to see if both valves open and close fully.
38 degrees at idle sounds like full unported intake vacuum is going to the advance. Ported vacuum would come off the carburetor from above the throttle plates and be applied as the throttle plates open. Can someone chime in to advise if there should be ported or unported vacuum on this application '64 98 with a 394?
January 13th, 2014, 03:51 PM
#26
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Location: Poteau, Ok
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Your issue is odd because an engine needs air, fuel, and well timed spark to run. If the valves are opening and closing properly (the same as the rest) and your compression is not that far off, then something you checked and said was present is not. Generally if the wired firing order is wrong, you would have 2 cylinders acting up and/or a back fire.
January 13th, 2014, 04:33 PM
#28
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Location: Atlanta, GA
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I would go with a NEW cap if you have not replaced that. I once tore down to the lifters and replaced all of them (63 Cadillac 390) and had the heads off and cleaned and the valves ground after replacing wires, plugs, points & condenser and cap. It ended up being the cap - even new and it had a crack. I saw it one dark night with the engine running...
January 13th, 2014, 06:34 PM
#29
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Hi I agree, something does not add up here.
I am going to re-do the compression test one more time and connect the timing gun to each individual wire and validate they are firing.
As i said i looked at the car running without the valve cover and the valves looked fine. But it is possible that they may not be opening fully and that could be causing the issue.
Lets say that a lifter was leaking faster than it should, that would cause the valve not to open properly or as long as it should open. If this was the case, would I still show good compression?
I am assuming that it probably would show good compression as the valves are closed during compression, correct?
I am going to re-do the compression test one more time and connect the timing gun to each individual wire and validate they are firing.
As i said i looked at the car running without the valve cover and the valves looked fine. But it is possible that they may not be opening fully and that could be causing the issue.
Lets say that a lifter was leaking faster than it should, that would cause the valve not to open properly or as long as it should open. If this was the case, would I still show good compression?
I am assuming that it probably would show good compression as the valves are closed during compression, correct?
January 14th, 2014, 05:40 AM
#30
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Join Date: Apr 2010
Posts: 978
Hi I agree, something does not add up here.
I am going to re-do the compression test one more time and connect the timing gun to each individual wire and validate they are firing.
I would not bother unless you do dry then oil down the cylinder walls.
As i said i looked at the car running without the valve cover and the valves looked fine. But it is possible that they may not be opening fully and that could be causing the issue.
Try turning over the engine by hand from the crank bolt to see if the rockers on cylinder #6 move as far as the others. Did you try to wiggle them?
Lets say that a lifter was leaking faster than it should, that would cause the valve not to open properly or as long as it should open. If this was the case, would I still show good compression?
Yes the compression would be good. Maybe slightly lower if the intake valve didn't open as much or for as long. You may have a lobe on the cam going bad.
I am assuming that it probably would show good compression as the valves are closed during compression, correct?
It would still be OK you are correct. Did you try the paper towel test?
I am going to re-do the compression test one more time and connect the timing gun to each individual wire and validate they are firing.
I would not bother unless you do dry then oil down the cylinder walls.
As i said i looked at the car running without the valve cover and the valves looked fine. But it is possible that they may not be opening fully and that could be causing the issue.
Try turning over the engine by hand from the crank bolt to see if the rockers on cylinder #6 move as far as the others. Did you try to wiggle them?
Lets say that a lifter was leaking faster than it should, that would cause the valve not to open properly or as long as it should open. If this was the case, would I still show good compression?
Yes the compression would be good. Maybe slightly lower if the intake valve didn't open as much or for as long. You may have a lobe on the cam going bad.
I am assuming that it probably would show good compression as the valves are closed during compression, correct?
It would still be OK you are correct. Did you try the paper towel test?
January 14th, 2014, 08:14 PM
#31
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Posts: 75
I will try two things this weekend
1. the paper towel test. What is the expected result if things work vs not working. I am assuming if the cylinder is working I should smell fuel?
2. I am going to test the spark strength, i was told the timing gun will show spark even if the spark is weak. I am afraid that maybe the petronix ignitor module may have a bigger gap than it should when it hits the #6 cylinder. The plug definitively shows that is not firing well as it looks fouled
Thanks for all of your help, I will keep u posted
1. the paper towel test. What is the expected result if things work vs not working. I am assuming if the cylinder is working I should smell fuel?
2. I am going to test the spark strength, i was told the timing gun will show spark even if the spark is weak. I am afraid that maybe the petronix ignitor module may have a bigger gap than it should when it hits the #6 cylinder. The plug definitively shows that is not firing well as it looks fouled
Thanks for all of your help, I will keep u posted
January 18th, 2014, 11:29 AM
#32
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Posts: 75
Hello All,
Something really weird is going on with this car. I did not run the car for a whole week. I started it this morning, as soon as it starts the engine is completely smooth, no misses, I could balance a coin on the intake manifold.
Run the car for 10 minutes and it starts miss firing again. I shut it off let it cool for 1 hour, start it again an it is miss firing.
I will do the paper towel test, run the compression test with the engine hot, and I am waiting for the spark tester to arrive on the mail today.
Does anyone have any idea, why would the car work perfectly fine for the first 5 minutes after one week of not running the car, and then as it warms up starts missing.
Thank you all for your help, I am trying to get to the bottom of this thing.
Something really weird is going on with this car. I did not run the car for a whole week. I started it this morning, as soon as it starts the engine is completely smooth, no misses, I could balance a coin on the intake manifold.
Run the car for 10 minutes and it starts miss firing again. I shut it off let it cool for 1 hour, start it again an it is miss firing.
I will do the paper towel test, run the compression test with the engine hot, and I am waiting for the spark tester to arrive on the mail today.
Does anyone have any idea, why would the car work perfectly fine for the first 5 minutes after one week of not running the car, and then as it warms up starts missing.
Thank you all for your help, I am trying to get to the bottom of this thing.
January 18th, 2014, 08:14 PM
#35
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Join Date: Aug 2011
Posts: 2,999
Could be a restricted passage in the carburetor from sitting causing a lean condition once the engine is fully warm and the choke plate is wide open. Try closing the choke plate slightly with the engine running warm and see if the miss changes. #6 may just be the first cylinder to misfire under lean mixture conditions.
January 18th, 2014, 09:17 PM
#36
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Join Date: Apr 2010
Posts: 978
Hello All,
Something really weird is going on with this car. I did not run the car for a whole week. I started it this morning, as soon as it starts the engine is completely smooth, no misses, I could balance a coin on the intake manifold.
Run the car for 10 minutes and it starts miss firing again. I shut it off let it cool for 1 hour, start it again an it is miss firing.
I will do the paper towel test, run the compression test with the engine hot, and I am waiting for the spark tester to arrive on the mail today.
Does anyone have any idea, why would the car work perfectly fine for the first 5 minutes after one week of not running the car, and then as it warms up starts missing.
Thank you all for your help, I am trying to get to the bottom of this thing.
Something really weird is going on with this car. I did not run the car for a whole week. I started it this morning, as soon as it starts the engine is completely smooth, no misses, I could balance a coin on the intake manifold.
Run the car for 10 minutes and it starts miss firing again. I shut it off let it cool for 1 hour, start it again an it is miss firing.
I will do the paper towel test, run the compression test with the engine hot, and I am waiting for the spark tester to arrive on the mail today.
Does anyone have any idea, why would the car work perfectly fine for the first 5 minutes after one week of not running the car, and then as it warms up starts missing.
Thank you all for your help, I am trying to get to the bottom of this thing.
I have two possible causes of the condition you are describing:
#1) The car ran smooth until it warmed up because the choke was on and limited air flow through the carb. This does not explain your weak spark or miss on cylinder #6. You could try holding your hand over the carb after it starts missing to see if it smooths out. Basically you will be simulating the choke. If it does smooth out, most likely you have a vacuum leak or a carb problem.
#2) I have seen a bad coil that starts to misfire after it gets warm. Hopefully you picked up the type of spark tester that you can open up the gap on to test the strength of the spark. It should be a sharp blue crisp spark. Not a dull yellow or orange spark.
Your problem of the misfire specifically on cylinder #6, still has me stumped. You switched everything in the secondary ignition, if it was in the primary ignition, like the coil, or Petronics unit, it would effect all the cylinders. If it was a carb problem, I would think it would effect all the cylinders. You might want to try to introduce some propane into the carb or around the intake to see if it smooths out.
January 19th, 2014, 10:31 AM
#37
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Join Date: Feb 2011
Posts: 1,168
What have you checked regarding a possible vacuum leak? Make sure the carb nuts are evenly tightened, then remove and plug all vacuum hoses from the motor including the vacuum advance can. Start and see if the miss goes away. If so, reattach one hose at a time, when the miss comes back that is the culprit. If not it could be a leak at the number 6 intake manifold port.
January 19th, 2014, 02:00 PM
#38
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Location: North Delta, BC
Posts: 1,067
Just a thought but you should exhaust all the other suggestions first. Is it possible there is a leaky head gasket that allows a little coolant into the cylinder when it warms up thereby causing a miss? Maybe re-torquing the cylinder head might cause a variation in what;s happening.
January 19th, 2014, 06:31 PM
#39
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Join Date: Aug 2012
Posts: 75
Hi All,
I have removed the vacuum lines going to the Power Break, AC/Heater, Distributor and plugged them all. The engine still misses when hot.
I bought a spark tester and noticed an occasional miss, not just in cylinder 6 but in the spark plugs of other cylinders. I opened the distributor and found that the ignitor module was touching the magnet ring slightly, so I fixed that.
I am ordering a set of points and a capacitor this week and putting it back to stock to try it that way.
The other question I have, is about the choke on the carb. How is that supposed to work?
When I look at the choke, it has a little metal tube that goes into it and is connected to the intake manifold. The choke has a little lever that is connected to the butterfly which is in the front half of the carb. I am not seeing that lever moving at all, is that supposed to move automatically depending on the car being hot or cold? It seems that the front butterfly is always wide open and never closed.
I am wondering if that has something to do with what I am experiencing? That is the car runs ok when is cold and started after a whole week of sitting and starts missing once it warms up.
All, thanks again for your help.
I have removed the vacuum lines going to the Power Break, AC/Heater, Distributor and plugged them all. The engine still misses when hot.
I bought a spark tester and noticed an occasional miss, not just in cylinder 6 but in the spark plugs of other cylinders. I opened the distributor and found that the ignitor module was touching the magnet ring slightly, so I fixed that.
I am ordering a set of points and a capacitor this week and putting it back to stock to try it that way.
The other question I have, is about the choke on the carb. How is that supposed to work?
When I look at the choke, it has a little metal tube that goes into it and is connected to the intake manifold. The choke has a little lever that is connected to the butterfly which is in the front half of the carb. I am not seeing that lever moving at all, is that supposed to move automatically depending on the car being hot or cold? It seems that the front butterfly is always wide open and never closed.
I am wondering if that has something to do with what I am experiencing? That is the car runs ok when is cold and started after a whole week of sitting and starts missing once it warms up.
All, thanks again for your help.
January 19th, 2014, 07:01 PM
#40
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Join Date: Sep 2012
Location: Water Wonderland MI.
Posts: 1,414
Really good thread, I also never heard of using timing light to check for spark to cylinders. As far as choke operation , with engine cold open throttle wide open and release, top choke plate should close, when you start engine choke will slightly open, as engine exhaust warms up intake crossover, choke should continue to open. Sounds to me your running lean mixture.
