Dead cylinder mystery

[Curban1]

I was hoping some smart people here could help me out. I have a 69 442 convertible with a 455 in it. The motor is basically stock as it was out of a car with 50,000 miles on it. It has new timing gears, aftermarket, distributor, cap, rotor wires, aluminum intake, and Holley carb with headers. the problem is the car will not run on cylinders five and seven.

The car starts fine idles with a choke on, warms up and idles on its own but it’s a very lumpy idle and those two cylinders are dead. They both have spark. They both have compression, and I’m presuming they both have fuel I don’t see how they couldn’t  but they will not run. I’ve tried changing the distributor, cap, rotor, and wires. Still, they do not fire.

 

Does anyone have an idea what could be going on here?

[edinmass]

More details........pull the valve cover and see if the rocker is moving on both holes......intake and exhaust. .......you could have a bad cam that isn't opening the valves............

 

If the valves are opening and closing, your diagnostic of fuel/spark is not correct. 

[Bloo]

5 and 7 wires swapped?

 

 

[BlueDevil]

Have you tried reversing the 5&7 plug wires. I believe they are next to each other on the dizzy cap.

 

I think the firing order is 1-8-4-3-6-5-7-2  counter clockwise, I think

[Curban1]

Thanks everyone for the responses, I should have said that I’m not inexperienced at diagnosing engines all though this one has me stumped. To answer some of the questions above the valves are moving I thought about the cam myself quite some time ago and eliminated that as the problem. 
I also thought perhaps the wires were swapped and check those they are correct. This is not something simple although I understand there’s only so many factors that would cause this and I thought I exhausted them all.

[Bloo]

How about a vacuum leak? A brake booster port often kills 2 cylinders if it has leaky stuff connected to it. I discounted that at first since it should not be 2 adjacent cylinders due to the manifold layout, but re-reading your post I see your manifold is aluminum. Is it aftermarket? If it is a single plane manifold, killing a couple of adjacent cylinders is possible. Also, your PCV needs to be connected to a dedicated PCV port on the carburetor. Is it?

[Curban1]

Those are some good points, however, upon checking, my brake booster is connected to the manifold on the opposite side beside cylinder number eight. The PCV valve runs from the valve, cover into the back of the carburetor. The manifold is aluminum dual plane Edelbrock performer rpm. I’ve run this exact combination several times on other engines that I’ve had in this car over the years set up the same way only difference being this is a new 600 CFM vacuum, secondary Holley carb, which I can’t see being the culprit. 
One question I do have is when I put the timing gears on what if they were off by a tooth? Could being off by one tooth do something like this?

[edinmass]

 

One tooth off would cause lots of running problems.......especially with a hot cam. Diagnose the problem, don't guess. 

 

Post all compression readings across the board........wet and dry.

Do a leak down test.

Check TDC and valve opening and closing as well as TDC.

 

Figure out first if it is mechanical then worry about fuel and ignition. One step at a time. Don't guess.

[Stude Light]

Hmmm. Seems like valve timing off would affect all the cylinders. You've got spark and compression. Maybe that rag that was forgotten and got stuck in the intake runner that serves those two cylinders?

 

I guess I'm with Ed and verify everything mechanical so you can cross that off the list. And verify you have spark at the correct time by ensuring it fires just before TDC on compression stroke on 5 and 7.

[gungeey]

4 hours ago, Curban1 said:

I was hoping some smart people here could help me out. I have a 69 442 convertible with a 455 in it. The motor is basically stock as it was out of a car with 50,000 miles on it. It has new timing gears, aftermarket, distributor, cap, rotor wires, aluminum intake, and Holley carb with headers. the problem is the car will not run on cylinders five and seven.

The car starts fine idles with a choke on, warms up and idles on its own but it’s a very lumpy idle and those two cylinders are dead. They both have spark. They both have compression, and I’m presuming they both have fuel I don’t see how they couldn’t  but they will not run. I’ve tried changing the distributor, cap, rotor, and wires. Still, they do not fire.

 

Does anyone have an idea what could be going on here?

You say  cyl #5 and #7 have fuel/spark/compression. And "they are dead" and " the car will not run on 5 and 7". I don't understand the complaint. What are 5 and 7 doing or not doing to be pinpointed?

[Curban1]

They are not fireing

[edinmass]

How do you know they’re not firing, do you have a five gas analyzer you can’t just guess. Why don’t you give us a detailed list of what you’ve done to the engine before you got to this position. Professional mechanics, you say process of elimination.

[gungeey]

1 hour ago, Curban1 said:

They are not fireing

Curban how have you isolated these two particular cyls as not firing? In other words, why do you say these two are a problem and the rest are ok?

[Rusty_OToole]

If those 2 plugs are not firing but the rest are, maybe there is a crack or fault in the distributor cap. Or, bad plug wires or bad plugs. Could be lots of reasons.

[Stude Light]

2 hours ago, Rusty_OToole said:

If those 2 plugs are not firing but the rest are, maybe there is a crack or fault in the distributor cap. Or, bad plug wires or bad plugs. Could be lots of reasons.

He says he has spark at those two plugs. My guess is he is grounding out the plugs on each of those cylinders (5 and 7) and finding no change in the performance but if he grounds any of the others it gets really bad but @Curban1 will have to verify that.

[Oldtech]

Compression? head gasket leaking between them?  You have covered most everything else. 

[Bloo]

A leakdown test would sort out that possibility right away. Just use a hose to listen to the spark plug hole of the adjacent cylinder while doing the leakdown test. Then listen again with the air shut off, to make sure you aren't fooling yourself by listening through a hose.

 

[Frank DuVal]

Ed is right, do a compression test first. And post the numbers here both dry and wet. Remember to tie open the throttle wide to do the test.

 

 

[Curban1]

Once again thanks for all the replies. I guess I will go through my diagnosis to help everyone understand what Ive done till now.

 

The car is idling rough and has low power. I've concluded these cylinders are not firing because when I pull a plug wire off any cylinder but these you can hear the engine miss on that cylinder. Except for 5 and 7, pulling wire here make no difference. I also see that the cylinders ARE getting spark by installing a plug in the wire that I have pulled off and grounding it. Plugs are all fine!

 

 

Compression checked out fine at 175 psi on all cylinders +/- 10% including # 5 and 7

I have tried 3 different spark plug wires on these cylinders, changed the cap and rotor twice with brand new units, tried different coil, and even 2 different new distributors. At this point I dont think its spark related.

I don't see any evidence of a head gasket being blown, no smoke out of pipes, no milky oil, does not run hot! Have not performed leak down but cant see that being an issue at this point ( am I wrong)?

Head gaskets were new.

 

I have looked for vacuum leaks but not around back of intake. Will try that when I have more time next week.

 

I almost feel like those cylinders are not getting gas but I m not one for sticking rags in my intake or heads during assembly for the very reason one could be forgotten. Can I be wrong? Will check this week as well.

 

What else have I missed?

 

Really appreciate the help and knowledge from you guys!! Pleasure speaking to people that understand engines compared to some of our local so called mechanics lol 

[Bloo]

1 hour ago, Curban1 said:

Have not performed leak down but cant see that being an issue at this point ( am I wrong)?

You generally don't need to if the compression is OK. When it isn't OK, you can hear where the leak is in a leakdown test so you know what to fix. I only suggested it in your case because you would be able to hear the leak if the head gasket were blown between 5 and 7.

 

1 hour ago, Curban1 said:

I don't see any evidence of a head gasket being blown, no smoke out of pipes, no milky oil, does not run hot!

A had gasket blown in-between 2 cylinders (and nowhere else) doesn't do any of those things. I would expect a problem with compression to show, but maybe not enough to arouse suspicion.

 

Is there by any odd chance an EGR valve? If there is, physically block it's ports temporarily with cardboard or gasket material or something so you can be sure no exhaust is leaking into the intake through a leaky valve.

 

20 hours ago, Curban1 said:

One question I do have is when I put the timing gears on what if they were off by a tooth? Could being off by one tooth do something like this?

It shouldn't kill individual cylinders. but I have seen it do that. I have some theories why, but that's not important right now. The whole engine will run terrible a tooth off whether it drops cylinders or not.

 

You can check that without taking too much apart. You must first absolutely verify your TDC mark. Never assume it is OK. I wrote a how-to for flatheads, but it is even easier with overhead valves. With all plugs out, and battery disconnected, use a positive stop in #1 plug hole. Flathead thread is here: https://forums.aaca.org/topic/388360-how-to-get-a-top-dead-center-mark-on-a-flathead-engine/

 

Once you are absolutely sure about TDC, you can pull a valve cover and watch the valves on #1. The important thing is that the overlap period is centered pretty closely around TDC. You want to watch the overlap period, so for instance if the firing order is 1-8-4-3-6-5-7-2, it takes two full crank turns to get through all that. You would be watching the valves on #1 while #6 is coming up on the compression/firing stroke. With all plugs out, battery disconnected, turn the crank ONLY CLOCKWISE with a wrench. What you look for is the intake opening before TDC and the exhaust closing after TDC. You can look up how many teeth the timing chain set has on the crank gear. Divide 360 by the number of crank gear teeth, and that is approximately how wrong it should be (compared to TDC) if you are a tooth off. Slop could conceivably put both events after TDC, but it shouldn't be off by enough degrees to equal a whole crankshaft gear tooth.

 

This is all edge case stuff, but considering what you have already checked, you are firmly in edge case territory. Nevertheless, before digging in too deep, I might be tempted to go back to the very beginning and check all the easy stuff one more time.

 

Edited April 21, 2023 by Bloo (see edit history)

[Mark Gregush]

Could it be something as simple as those two plugs are bad and not firing under compression? 

[edinmass]

Still the same problem…….explain what you have done to it recently. Check the rockers to be sure the valves are opening, or use a borescope to inspect them from the combustion chamber. It’s not a primary ignition issue……check the secondary. Taking a KV reading on all the plugs while it’s running might help. A five gas analyzer would help. If your intake valves are not opening from bad cam lobes is one mechanical possibility. Stop guessing, diagnose it. Check the valve operation to eliminate mechanical issues, then chase fuel, and finally ignition. Shouldn’t be difficult to figure out if you use a diagnostic routine instead of jumping all over and trying “maybe’s”. Why was the motor apart? Why does it have new head gaskets? Explain what was done.

[keiser31]

Check the wires again. Sometimes new wires are faulty.

[Frank DuVal]

15 hours ago, Curban1 said:

almost feel like those cylinders are not getting gas but I m not one for sticking rags in my intake or heads during assembly for the very reason one could be forgotten. Can I be wrong? Will check this week as well.

I took apart a Ford 429 that had been apart/back together and after a few years sitting (not in a vehicle) would not turn 360° with a wrench on the crankshaft. Red rag in one cylinder!

 

Take a borescope and look down the intake manifold to the intake valves on these cylinders.

 

Have you tried propane around the intake manifold or other mechanic tricks to find vacuum leaks?

 

And you really did try swapping #5 and 7 wires at the distributor cap?

[EmTee]

Look for an intake manifold leak in the vicinity of 5 & 7.

[MercMontMars]

Never trust your parts, especially distributors. If you know that everything is set right and yet it still won't work, verify the integrity of your parts. I've had it happen to me multiple times where I just couldn't figure out why it wouldn't work when I KNEW everything was correct and it turned out to be faulty parts right out of the box. Sounds like you might've tried that already though.

 

How do you know for sure it is cylinder 5 & 7? Have you verified your firing order and adjusted your timing? How are your spark plugs? Even in the worst scenarios a cylinder should still fire unless it has no connection to the distributor at all or isn't getting fuel.

 

This is more of a last ditch test, but try putting a little marvel mystery oil down these two cylinders, run the motor for a bit then shut it down and see if it was burned or not. 

 

Check your:

 

Firing order

Timing
Spark Plugs

Distributor

Fuel-Air Mixture

Swap your 5&7 wires on the distributor like others have suggested

 

I'm no professional, but I'm just offering advice collected from hours of cursing simple problems then feeling like a fool afterwards. Good luck!

 

 

Edited April 23, 2023 by MercMontMars (see edit history)

[roysboystoys]

This is a long shot. Is the distributor a points type? If so , check the points cam for wear and the shaft for play/looseness.

Being an aftermarket intake, possibly plug or casting core plug is missing , leaking on the under side.

Is there oil on the 5/7 plugs? You can have a vacuum leak on underside of the manifold that wont respond to your external tests.

What are the vacuum readings like. Low readings might indicate your cam is off by one tooth.

Did this ever run right , before the work that was done to it.

I made my living diagnosing engine performance problem's, but it's very difficult  over the internet.

Sometimes the ear , nose , experience are the tools that are needed.

Seems there are two firing order wire locations for 455 olds. I assume one is points and one is HEI?

 

Edited April 23, 2023 by roysboystoys (see edit history)

[Ltc4748]

Have you removed the plugs from 5 & 7 and looked at them. The reason I ask is they would be more white in color than the rest of the cylinders if they are running lean. I have also seen in the past that people would replace the plugs and during the process either did not check the gap or dropped them and closed the gap, this causes a constant misfire.

Since it had a new Holley carb installed did anyone correctly set fuel level and idle mixtures? If you close the choke by hand slowly (or restrict the air into the carb with your hand) and the engine begins to run smoother the mixture is too lean. If the mixture is correct closing the choke manually will make the engine load up without any improvement.

[roysboystoys]

Op hasn't been on forum since Tuesday.

Wonder if this got fixed.

[R Walling]

 A friend of mine tuned up his truck and it wouldn't start. He bought another dist. cap and it still would not start. 

Eventually after pulling out all his hair, he discovered that the two new dist. caps that he bought were made wrong!

 The manf. paid for all his troubles!

[pont35cpe]

This reminds me of a 1969 Cadillac my dad had bought with "dead" cylinders. Engine had been rebuilt by the previous owner. We took the engine apart, checked everything, put it back together, still, same dead cylinders. Everything checked good, timing, spark, compression. It took us awhile, but we finally found the problem. The Quadrajet carb had been removed, and a new base gasket installed without the thin metal plate. Without the metal plate, the engine sucks exhaust from the heat riser passage, and was feeding exhaust to the dead cylinders. Installed the metal plate, engine ran perfect.

[Curban1]

Hi everyone,

 

Nope not fixed yet but in my defense only had 2 hours in last week to look at it. Thanks for all the help definitely food for thought. SO I did manage to pull the carb and put a camera down the intake. Cylinder 5 no issue but cylinder 7 had a thin amount of silicone squirt into the joint between intake and head. maybe affected 10% of the port. Not near enough to block it but could definitely affect the flow. I'm considering pulling my intake to clean this up however wondering why cylinder 5 is affected with no tell tale issue showing up. Could this have created a vacuum leak for both cylinders ( no I did not have time to check)

[edinmass]

To have a vacuum leak bad enough to cause a lean burn misfire to the point the cylinder balance performance checks shows a “totally dead hole or two” would be such a large leak you could heat is from five feet away. Still guessing and not diagnosing. Did anyone to a KV check on ALL the holes? Or a five gas check out the tailpipe? Did anyone actually check to see if the rockers were opening the valves? It is actually possible to diagnose the problem without tearing the car apart guessing. It does take equipment that most people don’t have……….but it’s usually faster, easier, and cheaper to diagnose it than throw parts and money at it with no results.

[Curban1]

I did verify that rockers were opening and closing valves. none of the other things. As you said no equipment. No one in my area even wants to look at a car this age. Plugs are not burning lean either.

 

 

[TerryB]

15 minutes ago, Curban1 said:

I did verify that rockers were opening and closing valves. none of the other things. As you said no equipment. No one in my area even wants to look at a car this age. Plugs are not burning lean either.

 

 

That is a major issue with keeping an older car running.  I spoke with the owner of a 1941 Plymouth who has been having issues with his car.  The one shop that will look at it told him the backlog is six months before his car can be scheduled.

[Mike "Hubbie" Stearns]

Please don’t take this personally, I don’t mean to offend anyone. We are all just guessing to a certain degree. You need to go back to the basics. You need 3 things for an engine to run. You need air, spark, and air/fuel. You have checked off the compression. What do the plugs look like?  Are they wet or dry?  If they are wet, that means lack of spark. If dry, that means no air/fuel or really lean. If dry, you can locate just about any leak by using propane. Hook a hose on a propane torch and go around the intake runner for dead cylinders and carb. Once it starts firing the cylinder, you will know you need to fix. Mike

[dodge28]

Bloo is on track . He is always on track.

Harry.

[dodge28]

Mike"Hubbie" Stearns, You and I think alike. Your advice is better than all. Simple approach. Normally when 2 cylinders side by side has no compression the offending part is a leaky gasket.

[Curban1]

car has pretty even compression across all cylinders at 175 psi

[dodge28]

In a case of leaking gasket the 2 offending cylinders will have the exact same compression, number for number, The next suggestion is try new spark plugs. It is not strange for brand new spark plugs to malfunction. Try cranking at night with the garage lights off and looks for sparks in the vicinity of the offending cylinders.