Odmark

Hello. Time for the first mishap i guess. When i started the car after work yesterday, it had lost 2 cylinders. I have replaced all spark plugs and plug wires, double checked firing order and its correct, checked intake for leaks=none.
Very nice spark, but still not working.
After driving for a while i now checked the plugs, the ones that are working looks perfect but the 2 thats not are completley dry and look never used at all.

What the hell can cause this? No bad sounds from the engine. Not had the chance for a compression test but if low compression would be the issue it would show on the plug right?

MDchanic

Are your valves opening?
Have you checked compression?

Plugs should be wet and oily if a cylinder is running without a spark, but to be "clean," I would expect that you'd have a valve problem.
I'd check the rockers, pushrods, and lifters, and then the cam, especially if it's a new one.

- Eric

Ozzie

Välkommen
Which two cylinders are "dead"? Were they working correctly after the ignition work you did? Are you getting a correct spark at the dead ones? If so, a compression check may be needed. Sometime a compression problem will not immediately become apparent by looking at the spark plugs.

Rickman48

Compression check won't show a flat cam.
Pull the valve covers and see if all valves are opening.
Might be broken rocker stands, bent pushrods, even broken valve springs, all which should be visable.
Did anything unusual happen previous to 'dead' cylinders??
Which cylinders are dead??
Mileage on motor??

J-(Chicago)

I would guess broken pedestals and ****-eyed rocker arms first. Those pot metal pedestals are pretty lame

Odmark

Hi again! Cylinders 6 and 7 are the ones not working. Superb spark on all plugs but still nothing on 6-7. Just pulled the valve covers and checked. Everything works as it is supposed to.
Nothing unusual happened, worked perfectly couple of hours before, but when i got off work the 2 cylinders were gone.

Still havent got the tools for compression test, hopefully i get some help tomorrow.

By the way! Seems like the cylinders pop to life sometimes when you put the pedal to the metal, sometimes its just slow and sounds tired, even when you kick down. And sometimes it revs fast and goes like stink.

Edit: Mileage on motor is about 9000 miles

m371961

Rickman, I thought a comp check will show extreme cam flatness (wipe out?) on the intakes, but you should see it comparing closely the operating range of the rockers.

Odmark

Both the 6 and 7 plug looks like they get no fuel/perfect combustion.

MDchanic

How, exactly, have you determined that those two cylinders are not working?

- Eric

Odmark

Pulled the wires while engine was running, nothing happened when i pulled 6 and 7, but when i pulled the other ones the idle got worse.

Ozzie

It seems very unlikely that a mechanical problem would affect two cylinders the same way on opposite sides of the engine in a matter of two hours when the engine was not running. Is the engine being fed by a conventional manifold and carburetor? Are you sure that the sparks are coming to those two dead cylinders at the correct times? While #6 & #7 are likely being fed by the same side of the carburetor, two other (good) cylinders are also being fed by the same side. So, if the engine is using a carburetor, it seems unlikely that it is the problem. While it is good to also do a compression check (anyway), it may not reveal a problem which developed in a two hour period of no operation of an engine.
If you are sure that you are getting "fire" to the spark plugs at the correct time, perhaps you should remove those two plugs (# 6 & 7) from the engine, and test them outside of the engine. I have had new spark plugs which were "duds" due to an internal problem.

Odmark

It is possible the engine ran this way before, but i think i would have noticed because the whole car is trembling badly at idle.
Will do a compression test asap, hopefully tomorrow if i get the tools.

The wierdest part is that it seems that the cylinders get no fuel, though the valves seem to operate.

Edit: It is the stock intake manifold and an edelbrock carb apparently. I havent checked ignition with stroboscope but the firing order is correct and the car fires up very easily even in -15 to -20 degrees celcius.

Seff

My 350 fired up and ran with 3, 5 and 7 disconnected, though the power was bad. Managed to reverse it 25 meters, it almost died when I held it on the brake, though. So you can definitely do that.

joe_padavano

Try swapping the plugs in cylinders #6 and 7 with two from cylinders known to be good. If the problem moves to the other two cylinders, replace the plugs.

Odmark

Already did and the cylinders not working are still the same. Also as i wrote earlier all the sparkplugs and plug cables are replaced.

Ozzie

Have you looked closely at the distributor cap? Is there any cracking, carbon tracks, or other problems? You could check those new spark plug wires with a VOM and compare the resistance to the specifications, just to be sure they are good. It appears that your problem is not an easy one, and everything must be checked. Assume nothing until it is verified.

MDchanic

Yes, but just remember that the usual reason for failure of spark plug wires is leaky insulation, NOT open conductors, so, no matter what, your wires will probably test out at a few thousand ohms (provided that they are "suppression" wires, and not straight copper or stainless steel, which would be ØΩ).

- Eric

LoganMiller68

I don't know if I missed it somewhere, have you performed a compression test yet? See if either of those two cylinders are holding pressure. Perhaps your valves aren't seating properly

lemoldsnut

A quck pull of the valve covers will tell is the rockers are working correctly. that will tell you if you have a flat cam, or broken pedastles which is a common problem. That and if you have a timing light hook it up to those spark plug wires and see if the light comes on when you start the motor that will tell you if you get spark as far as the timing light connection.
Then if those two work I would go to a compression check.

Odmark

Ozzie: Distributor cap checked and looks perfect. Will measure the spark plug wires tomorrow.
LoganMiller: Have not done compression check yet, havent got the tools. This sunday im borrowing a compression tester from a friend.
Lemoldsnut: I have checked under the valve covers and everything is operating correctly. Also going to borrow a timing light on sunday to check that out.

oldcutlass

What distributor do u have in there. If its electonic it may have gone bad.

Odmark

I believe i have the stock distributor.

oldcutlass

I just can't see having issues on both banks. Replace the new wires and the new plugs with known good ones. I'm thinking it's either a bad module, cap, or bad wires and plugs. Or the wires are not seated.

compedgemarine

on two different occasions I have broken valve springs on mine. stock 70 442 with the stock springs. on both occasions I shut the engine off and noticed that it shook funny right when it shut off. fired it back up and had a dead cylinder. first time I replaced all the valve springs as a precaution. several months later it did the same thing, the same way. swapped the broken new one with one of the originals I took off and it has been fine for years and thousands of miles. dont know why it did it.

64Rocket

I tend to agree that may have a couple of broken valve springs.
Another possible problem is if you have "Pertronic's" conversion on your stock dizzy, you may have lost a couple magnets off the trigger wheel. It has happen to me.

Gene

Odmark

Compression test done know! About 11kg on all cylinders. Valve springs checked and they are not broken.
Tried replacing known good wires with the ones at faulty cylinder but problem persisted.

This has to be a fuel delivery problem, i have driven about 600 km now and the 6-7 plugs still look brand new and there is absoluteley no smell of fuel at all.
I dont really know how 4 barrel carbs work, but does it feed 2 cylinders per barell?

Seff

No, the left(driver's side) primary and secondary feeds 1, 4, 6 and 7, the right(passenger side) primary and secondary feeds 2, 3, 5 and 8.

6 and 7 are fed rearward from the driver's side of the carb. Since your ignition and valvetrain check out, I'd look into finding out if there is some kind of block in that part of the intake. Before you start poking coat hangers or stuff like that through, use a mirror and scope it out. You don't want to flush any debris there MIGHT be into your cylinders.

I'm thinking bird's nest or something like it here.


I'm having a hard time believing that an incorrectly adjusted idle screw would still supply fuel to cylinders 1 and 4 without sending any significant amount to 6 and 7. Feel free to correct me on this, I'm really not sure.

Odmark

Checked out the intake but couldnt really find anything, going to buy new gaskets tomorrow and remove the whole thing. Gasket for the carb was broken as well between two of the primarys i guess?

Fuel is coming from the carb but it was all black on the barell that feeds 6-7.
Will take pictures tomorrow, quite hard for me to explain.

compedgemarine

most of us are un the US so we go by PSI which is a smaller increment. you say about 11kg but what you are looking for is no less than about 10% difference. what exactly were the readings for each cylinder? it is possible that the intake valve is not sealing well on those two cylinders or you could have a vacumm leak at the intake on those two.

Seff

Just a dumb question: since two of the three manifold vacuum holes are in the 6-7 intake tube, did you check all the lines and fittings connected to those two to make sure there isn't a massive vacuum leak on them? That would mean those two cylinders suck in normal air, while 1 and 4 suck in all the fuel.

m371961

Both replies above are good ones.
I would think if it is electrical plugs would be dirty, but wouldn't they be clean if those cylinders are running lean due to vacuum leak, cracked intake etc?
I am curious now, want to see what is found.

ctsplicer

Remove the dead mouse from inside the intake.Ask me how I know.

Odmark

Problem solved! Bit ashamed to say this but it was a vacuum line that had come loose. Thank you all for your help, i really appreciate it.

Ozzie

Congratulations! At least it was a low cost fix. Some of our guys were "closing in" on the problem. I'm still learning some things from the forum.

Seff

Getting close? I totally nailed it in my last post, man.

MDchanic

DING DING DING!!

Looks like the Ameri-Dane did nail this one.

Good work, Seff! I will humbly admit that I didn't even think of a vacuum leak.

- Eric

Seff

It's about time I paid this site back for all the help, so you're welcome!

Now, Odmark, what's the next problem? There's always another problem.

Odmark

Well the only real problem i have now is where the fuses are located

Seff

On the inside of the firewall, between parking brake and pedals.

Odmark

Found it! Thank you Not a very good spot to put the fuses, well well replaced now and the wiper works again