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No power out of #6 cylinder

No power out of #6 cylinder

Old June 18th, 2018, 06:28 PM
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No power out of #6 cylinder

Hello ladies and gentlemen,
I have a situation here that's hurting my head. I have a 455 in a jet boat that I just picked up, I just upgraded to a new HEI ignition, and a new Demon carb. When I test run it, I'm getting a miss in #6 cylinder. The wires are in the correct order and it's getting spark, I pulled the valve cover and the rocker arms are cycling the way they should, I've swapped different wires and plugs, I've check for vacuum leaks, and swore at it and called it everything but a child of God and still no power out of this cylinder. I'll be bringing a bore scope home tomorrow to look into the intake area from the manifold (single plane torker ) . The old carb was still on the engine when I got it, so I doubt anything got down in there, but I'm grabbing at straws now. I'm no master mechanic, but I do know my way around an engine enough to get myself into trouble, but this one is cooking my noodle. What am I missing guys, any help would be greatly appreciated.
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Old June 18th, 2018, 07:05 PM
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Are you getting compression? You may have a valve that is sticking and not closing all the way or even a bent valve.
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Old June 18th, 2018, 08:03 PM
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That particular cyl. is @ 137 psi. they're all within 12-19 psi of each other
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Old June 18th, 2018, 08:14 PM
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I have told this story a few times before but it may apply here too. I once had an old BowTie pickup that had a miss when I traded for it. Did a tune-up including points, condenser, cap, rotor, plugs, and wires. Tuned carb and set timing. Still had a miss. Replaced the dist. with an HEI and new wires again. Still had a miss. Found a freshly rebuilt set of heads and replaced those along with new intake and carb. Still had a miss. Replaced cam and lifters, still missing. Ended up sitting on the livingroom floor hugging my knees into my chest wondering what to do and my loving wife asks if I replaced the plugs? "Of course!", I replied and then she says "Replace them again, they're cheap aren't they?" I replaced them again with AC Rapid Fire plugs and that engine ran GREAT!

Try a new set of good plugs?
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Old June 18th, 2018, 08:29 PM
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I'll give anything a shot right now. On the way home from work I'll pick up another set of plugs and try that, along with the borescope.
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Old June 19th, 2018, 05:09 AM
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Before spending ANY money on plugs or anything else, simply swap the plug in the bad cylinder with one in a good cylinder. If the problem moves to the new cylinder, you've found the cause. If not, the plugs have nothing to do with it.
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Old June 19th, 2018, 06:28 AM
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Yes, I've put a different plug and wire on and still no power out of this cylinder. I'm getting spark, I'm just not sure about fuel. Like I said, the valves are cycling like they should, but it's acting like it's not getting fuel. I'm going to run a borescope down through the intake tonight when I get home from work.
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Old June 19th, 2018, 06:33 AM
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What does the plug from that cylinder look like? Black and wet? If it's sooty, gas is getting in. Run a leakdown test. You likely have a blown head gasket or worse.
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Old June 19th, 2018, 08:36 AM
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Originally Posted by joe_padavano View Post
Before spending ANY money on plugs or anything else, simply swap the plug in the bad cylinder with one in a good cylinder. If the problem moves to the new cylinder, you've found the cause. If not, the plugs have nothing to do with it.
Not true Joe! The above example was with many swapped plugs and wires. Even the distributor, wires, carb, intake, heads and camshaft. But I kept putting the same plugs back in. They were still new, right?!!! Change the plugs! They are the cheapest part in the equation. Buy a single for the dead hole and try that first, you can get a good plug for just a couple dollars.
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Old June 19th, 2018, 10:57 AM
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Originally Posted by tsansi View Post
I have a 455 in a jet boat that I just picked up,
I just upgraded to a new HEI ignition, and a new Demon carb. When I test run it, I'm getting a miss in #6 cylinder.
The wires are in the correct order and it's getting spark,
I pulled the valve cover and the rocker arms are cycling the way they should,
I've swapped different wires and plugs,
I've check for vacuum leaks,
and still no power out of this cylinder.
137 psi in that cylinder and they all run within 12-19 psi

No mention if the engine had a miss before he picked it up.
No mention what the plug looked like in #6.
No mention of what type lifters in the engine.
What does the oil and oil level look like ?
Are the valves in #6 opening and closing all the way ?
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Old June 19th, 2018, 02:10 PM
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Originally Posted by cjsdad View Post
Not true Joe! The above example was with many swapped plugs and wires. Even the distributor, wires, carb, intake, heads and camshaft. But I kept putting the same plugs back in. They were still new, right?!!! Change the plugs! They are the cheapest part in the equation. Buy a single for the dead hole and try that first, you can get a good plug for just a couple dollars.

Apply a little common sense. Say there is a misfire in cylinder #6, all others work fine. Put the spark plug from #6 into #7 and vice versa. If the plug formerly in #6 fires correctly in #7, the problem is NOT the plug. Conversely, if the plug from #7 fires correctly in #6, the problem is clearly the old plug. No purchase of anything is required to check this.
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Old June 19th, 2018, 07:11 PM
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Originally Posted by joe_padavano View Post
Apply a little common sense. Say there is a misfire in cylinder #6, all others work fine. Put the spark plug from #6 into #7 and vice versa. If the plug formerly in #6 fires correctly in #7, the problem is NOT the plug. Conversely, if the plug from #7 fires correctly in #6, the problem is clearly the old plug. No purchase of anything is required to check this.
As you say... Apparently I wasn't there at all.
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Old June 20th, 2018, 06:47 PM
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Ralph, I did test run it on the trailer before I brought it home and it did run a bit rough, but I just chalked that up to the very well "seasoned" thermoquad that was on there at the time, we only ran it long enough to get a bit of heat into the engine because we didn't have a water supply handy for cooling. The plug out of # 6 looks very much like the rest of them, although I will say that it's considerably cooler to the touch when I pull it to check after a run than the others. I'm not the best at reading plugs, but the rest are fairly dark brown-black and smell a bit of gas which tells me it's a bit rich and I can smell that while it's running, but this one, while it looks about the same as the others, there's no smell of fuel nor is it wet. As for the lifters, I really couldn't tell you, I've never had this engine torn down so I'm going to assume standard hydraulic. And for the lift, my dial indicator is in storage right now otherwise I would have those numbers for you guys also, but when I had the valve covers of and just eyeballing it, there appears to be the same amount of lift and duration as the rest of them. The oils is full and fresh, the previous owner had just changed it getting ready for this season when he found out he was expecting another bundle of joy, and the boss said that this toy had to go. As it stands right now, I'm dead in the water (no pun intended). The bore scope that I was going to bring home from work was mysteriously missing from the tool crib, so it won't be till Friday before I can get the other one off of the service truck to bring home. Keep throwing the ideas out there fellas, my bag of tricks is just about empty.
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Old June 20th, 2018, 09:41 PM
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Originally Posted by tsansi View Post
Ralph, I did test run it on the trailer before I brought it home and it did run a bit rough, but I just chalked that up to the very well "seasoned" thermoquad that was on there at the time, we only ran it long enough to get a bit of heat into the engine because we didn't have a water supply handy for cooling.
That would seem to tell me it had a pre-existing condition. And I'll bet the previous owner knew it.

The plug out of # 6 looks very much like the rest of them, although I will say that it's considerably cooler to the touch when I pull it to check after a run than the others. I'm not the best at reading plugs, but the rest are fairly dark brown-black and smell a bit of gas which tells me it's a bit rich and I can smell that while it's running, but this one, while it looks about the same as the others, there's no smell of fuel nor is it wet.
Plugs should never be wet with fuel. Try a brand new plug to see what color it burns like. It may have got the color from being in another cylinder ?


As for the lifters, I really couldn't tell you, I've never had this engine torn down so I'm going to assume standard hydraulic. And for the lift, my dial indicator is in storage right now otherwise I would have those numbers for you guys also,
A dial indicator would tell you exactly if the valves were opening and closing all the way. If you get less on #6, then I would start suspecting cam lobe, collapsed lifter, push rods, rocker arm/pivot wear or something on #6.

but when I had the valve covers of and just eyeballing it, there appears to be the same amount of lift and duration as the rest of them.
A dial indicator will be helpful.

The oils is full and fresh, the previous owner had just changed it getting ready for this season
AHHHHHHH. And no water in the block will hide a cracked head or blown head gasket. Fresh oil change and you can't tell if there was water in the oil.


when he found out he was expecting another bundle of joy, and the boss said that this toy had to go.
Forgive me, but that sounds like a great line.

As it stands right now, I'm dead in the water (no pun intended). The bore scope that I was going to bring home from work was mysteriously missing from the tool crib, so it won't be till Friday before I can get the other one off of the service truck to bring home.
You might not see the problem with a borescope.

Keep throwing the ideas out there fellas, my bag of tricks is just about empty.

I think you may be getting power from #6, its not like you have no power from #6. I think crack in the head or block gets bigger if its warmed up. You may have to pressurize the cooling system with water.
........Just my guess about things from here.
Good luck.
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Old June 20th, 2018, 10:02 PM
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Ya know Ralph, the deeper I get into this, I'm tending to agree with you on the AAAHHHHAAA moments and a great line. This was a younger guy, and he and his wife seemed legit, but I'm thinking maybe not. I was beginning to get fairly frustrated with it this evening, so I took a break from tinkering with it. I will say that I have hooked up the hose to it so I can run it longer and I've ran it for approx. 15-20 minute on the trailer with around 10 psi on the water gauge. Shows no water in the oil so far, but it is a water cooled exhaust, so looking for steam is kind of a moot point. I'm afraid that I'm going to have to at least top half this engine before it's all said and done.
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Old June 20th, 2018, 11:31 PM
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Originally Posted by tsansi View Post
Ya know Ralph, the deeper I get into this, I'm tending to agree with you on the AAAHHHHAAA moments and a great line. This was a younger guy, and he and his wife seemed legit, but I'm thinking maybe not.
I have met people of all ages that mis-represented things. How long did he own it ?

I was beginning to get fairly frustrated with it this evening, so I took a break from tinkering with it.
Best thing to do is walk away when frustrated. We stop thinking clearly because we are upset.

I will say that I have hooked up the hose to it so I can run it longer and I've ran it for approx. 15-20 minute on the trailer with around 10 psi on the water gauge. Shows no water in the oil so far, but it is a water cooled exhaust, so looking for steam is kind of a moot point. I'm afraid that I'm going to have to at least top half this engine before it's all said and done.
Lets see what we find out

A dial indicator will tell you about the valves opening and closing all the way.
A timing light in #6 plug wire will confirm spark or not when its running.
I am not sure a borescope will find a problem if there is a crack in the head or block or a blown head gasket.
Go slow and hang in there, you'll get it figured out.
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Old June 22nd, 2018, 06:21 AM
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I battled a cylinder miss in my 455 for quite a while. After replacing many items I did a cylinder leak test and found #8 had over 45% leakage.
I pulled the heads and found a very bad exhaust valve guide.
Joe
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Old June 24th, 2018, 07:21 AM
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Okay ladies & gentlemen, this is going to be a testimony about not getting in a rush & to double check yourself from time to time. After sevaral days of not being able to work on this motor, I get back out there and decide to start from scratch. I run another compression test and apparently I need remedial training on how to use the damn thing. On my first test, several days ago, I must have not released the pressure on the gauge itself when I went from #4 cylinder to # 6, thus it looked like I had 137 psi in that cylinder. Last night when I ran the numbers, # 6 only has 30 psi, so there's my problem. I couldn't find my oil squirter last night, so when I get home this afternoon I'll get some oil down that hole to see if compression comes up (bad rings), or stays low (bad valves). I'm hoping the problem is in the heads because I really don't want to pull this motor. I'll keep you posted. Thanks for listening to my rant.
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Old June 24th, 2018, 10:48 AM
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That kinda changes everything. Hope it is just a valve and can be repaired easily.
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Old June 24th, 2018, 11:18 AM
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Yup, I feel like bright shiney newbie right now. I haven't pulled a stunt like that in a loooong time.
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Old June 24th, 2018, 01:00 PM
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Things are looking better.
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Old June 24th, 2018, 01:02 PM
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This is interesting b/c I have 0 compression in #7, and minimal compressions in the other 7 cylinders. I've been told my engine needs a complete rebuild.
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Old June 24th, 2018, 01:29 PM
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Originally Posted by 72convert455 View Post
This is interesting b/c I have 0 compression in #7, and minimal compressions in the other 7 cylinders. I've been told my engine needs a complete rebuild.
You can do a lot of diagnostics with a compression and leak-down test. If you aren't looking to do a complete restoration you may find all you need is timing chain repair, valve job, and gaskets. But, you could also need a complete rebuild. Time to do some homework!
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Old June 24th, 2018, 08:18 PM
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Well, the prognosis is grim. I put oil down the hole, spun it over & she jumped up to 90 psi. So it looks like a lower end build is in the future for me. What burns me is that, just for giggles, I ran the scope down that hole and you could clearly see a nice, pretty cross hatch on the cylinder walls. Methinks that whoever put this together in the past, boogered a ring while they installed this piston and just didn't catch it. So now I need to decide if I'll just hunt for a good, fresh short block, or do I rebuild it myself, which I can do and have done more than once, the only draw back is that I don't even have a garage to work from right now, I'll be in the outdoors while doing this.
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