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Bizzare Dead Cylinder. Long Story 700 1992

posted by someone claiming to be 289 on Thu Jul 28 18:13 CST 2022 [RELATED]

1992 Regina 740.

Developed an idle only misfire in number one cylinder. I can pull the plug wire or injector wire without change in engine sound. All other cylinders have a large change when plug wires are pulled. Start it cold and I can easily touch the number one exhaust manifold header.

If I chock the wheels and put it in drive the number one cylinder will try to fire ( By going to the back of car to check exhaust sound) If I brake torque it the dead cylinder comes alive and there is no misfire. But I think it is weak.

What I've done:

Swapped the number one plug wire and spark plug. No change.

Swapped injectors 1 and 2 plus connected the number 2 injector wire to number 1 injector. No change.

Injector balance test with injector tester. All injectors test within 1 psi of each other. Fuel pressure is dead on and regulator is working and not leaking.

Checked cam timing, belt is tight and marks are dead on

Checked for vacuum leaks and sprayed carb cleaner all over the intake and hoses.
Pulled intake manifold anyway and checked gasket and manifold for cracks all ok.

Pulled distributor cap and rotor ( 4 year old Bosch ) Ok no cracks or carbon tracking.

Checked ignition timing ( diagnostic purposes only) 10 degrees BTC.. Ok

Cold compression: 1-4 all between 175 and 177 psi.

All engine and body grounds listed in the faq.

Head gasket, valve seals and valves lapped 4 10,000 miles ago. ( for fun )

I did more but I think this is enough....Thanks to everybody who has read.

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Bizzare Dead Cylinder. Long Story 700 1992

posted by Dave Stevens on Fri Jul 29 02:29 CST 2022
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As you move slowly away from idle, does the misfire disappear almost immediately? Does it stumble and hesitate for just a brief moment until the revs are say 1800? Or does it stumble and hesitate for quite a while before it finally smooths out at say 1800? Does the misfire behave signficantly different between a stone cold and warmed engine?

If your testing descriptions are correct about #1 always being the only misfire at idle under all the permutations you describe then the distributor is one of the few remaining things you haven't swapped that are cylinder specific. Inspect carefully for signs of corrosion, damage or an ill fitting contact in the #1 ignition wire socket in the distibutor cap as well for excessive wear or pitting on the #1 contact stud inside the cap. Many recommend using dielectric ignition grease inside the ignition wire boots to keep moisture out. I know your distributor cap/rotor are only 4 year old Bosch, but if there's any chance you still have the old ones around it would well be worth a try to see if that changes the symptoms. A worn distributor shaft seal or bushing could be an aggravating issue for premature cap/rotor failure. Any evidence of oil leakage from under the cap at the back? inside the cap at the bottom? inside at the back behind the rotor?

Any chance your charging system or battery aren't up to snuff? Significantly weaker voltage at idle could help explain misfires. Any difference in your symptoms when moving away from idle when all loads are on (headlights, fan hi, 4-way flash, de-fog,etc.) compared to all loads off?

Before you started moving things around, did you read and compare all four spark plug tips? Differences in colour, fouling and wetness can tell you a lot when just one cylinder is involved. Any chance you have unexplained coolant loss and #1 plug is notably cleaner?

If you hadn't described all the testing you did, my first guess would have been bad ignition wires, like a weak contact at the #1 spark plug boot. Sometimes simply using pliers on the outside of the boot to pinch in the contact collar so it will fit tighter on the spark plug can help with such matters.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

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Bizzare Dead Cylinder. Long Story 700 1992

posted by someone claiming to be 289 on Fri Jul 29 12:03 CST 2022 [RELATED]

Thank you.

About off idle behavior. When I brake torque it the misfire goes away at about 1000 RPM. I can pull the number one plug wire or injector wire and I can hear the cylinder cut out. No stumble at all it just comes alive. if I rev it to 3000 RPM in park and pull the number one injector wire there is a noticeable change. If I pull the number two injector wire there is a bigger decrease in RPM.

Cold or hot its always the same. And it starts every time without any hint of trouble.

Plug wires were new ( Napa Belden ) in April.Changed Just for maintenance. I swapped back to the old wires ( thinking new does not mean good) and still no change. I only use plug wire pliers ( soft coated ) The old plugs looked normal with the number 4 having some oil ash. No coolant loss at all and its as clean as it was 4 years ago when I did the head gasket for fun.

Checked for oil in distributor, none and for play in the distributor bushing. No radial play, some minor end play only. No corrosion on terminals in cap or where the wires connect.

I swapped the coil pack from my 1992 Regina 940 and no change. Spark intensity is the same as my 940.

Battery is new and voltage is over 14 volts running. I will check about loading the electrical system.

Additional clues. When I inspected the cylinder walls during the head gasket change I could see blow by marks. I do not remember which cylinders.

Valve adjustment is .017 to .019 and has not changed in 14 years. Sticker says .016 to .018.

Vacuum gauge readings are normal. Except that the needle vibrates so much I worry it will break the gauge. I lapped the valves and replaced the valve seals during the head gasket change and remember it did not make a change in vacuum.

Sorry for the length

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Bizzare Dead Cylinder. Long Story 700 1992

posted by Chris Mullet on Sat Jul 30 14:31 CST 2022
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last visit: Fri Oct 24 09:08 CST 2014

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Assuming you’ve exhausted all possible ignition points of failure (including dropping in a new set of copper/nickel core spark plugs).

“ …Vacuum gauge readings are normal. Except that the needle vibrates so much I worry it will break the gauge…” by

That’s kinda interesting. I’m not sure how smooth the needle should be on a four banger but it starts to make me think intake manifold leak. Does the needle quiver at a frequency like once every other revolution or more like EVERY cylinder causes a quiver or is it impossible to tell? I could get real crazy and suggest a cam lobe is wearing flat. It would cost nothing to check.

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Bizzare Dead Cylinder. Long Story 700 1992

posted by Amazonphil on Tue Nov 8 13:45 CST 2022
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can you check compression?
I had an engine where it mysteriously was cracking one of the insulators I think cyl 3 near the electrode of the plug. a few years later it blew a head gasket, I suspected later that the plug was maybe getting wet. it was whiter than the others. next time you pull the plugs check the electrode to see if it has a hairline crack in it. I think maybe it was sparking through eh insulator crack and not through the plug electrode. I did not at that time see head gasket failing symptoms. they were bosche plugs and I had it happen maybe 3 times.

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Bizzare Dead Cylinder. Long Story 700 1992

posted by Amazonphil on Tue Nov 8 13:52 CST 2022
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another thing i just found was that I puled a plug wire , it was an original "boogycord" plug wire. there is a stainless steel tube that fits over the spark plug and it came out of the end of the plug wire. I think it might pull away a bit and cause an issue there, You already swapped plug wires though. i ordered some online and they came but they were such cheap junk.. Id stick with OEM bosche "boogycord" ones.

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Bizzare Dead Cylinder. Long Story 700 1992

posted by Chris Mullet on Thu Jul 28 22:33 CST 2022
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last visit: Fri Oct 24 09:08 CST 2014

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Have you tried pulling all four plugs, connect them to their leads, ground them, have an assistant crank the engine over, and visually compare spark intensity between all four?

How old are the plugs and what type are they?

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Bizzare Dead Cylinder. Long Story 700 1992

posted by someone claiming to be 289 on Fri Jul 29 11:02 CST 2022 [RELATED]

I pulled all the plug wires and they all have the same spark intensity with the engine running. The plugs were in for about 20,000 miles and look great except for cylinder 4 which has minor oil ash residue. The wires were changed for maintenance in April. I changed all the plugs and the number one cylinder remains dead only at idle. I also swapped the old wires back without any difference.

Spark intensity is exactly the same as my identical 1992 940 Regina.

Thank you for helping.

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