Diagnostic Challenge!

[Matt Harwood]

OK, new distributor cap arrived and it was identical to the old one so it fit perfectly. Actually, it's better than the old one, with brass terminals instead of aluminum.

Unfortunately, #2 cylinder is still dead.

Now what? I'm out of ideas.

[W_Higgins]

How about a dynamic issue like an exhaust valve hanging when running but not when cranking for a compression test?  Put a vacuum gauge on it and read your problem by how the needle reacts.

 

 

[TerryB]

Can you verify you have spark when engine is running?  Can you see the spark generated?  Is it weak or intermittent?  

[PFitz]

Clamp an inductive timing light on the #2 spark plug wire and make sure the plug is firing in the cylinder.

 

Paul

[Studeous]

This is a case for Gus....

[Studeous]

Might I suggest a shiny new plug for #2. And a substitute wire for same. Perchance the plugs and or wires got jumbled when swapping? You know, “in all the excitement, I lost count” kind of deal. Good luck cause you covered about anything else. 

[joe_padavano]

49 minutes ago, Studeous said:

Might I suggest a shiny new plug for #2. And a substitute wire for same. Perchance the plugs and or wires got jumbled when swapping? You know, “in all the excitement, I lost count” kind of deal. Good luck cause you covered about anything else. 

 

Go back and read post #1

[Bloo]

It is time to have a good look at the closest barrel of the closest carburetor.

 

Does this setup have idle jets on all carbs or just the center? Is it progressive linkage?

 

It is truly amazing how small a vacuum leak can be and still kill a cylinder, particularly if the leak is out on a runner.

Edited July 2, 2020 by Bloo (see edit history)

[edinmass]

3 hours ago, Matt Harwood said:

OK, new distributor cap arrived and it was identical to the old one so it fit perfectly. Actually, it's better than the old one, with brass terminals instead of aluminum.

Unfortunately, #2 cylinder is still dead.

Now what? I'm out of ideas.

 

Fix it.

 

Sorry..........all those terrible thing they say about me are true.

 

You need a KV tester. I realized I didn’t have one down south when we were talking about this thread, so I ordered one, It will be here next week. Compression, fuel, and spark......boom. If only it were that easy. Did you do a cylinder power balance test? I would still look for vacuum leaks.......most likely the cause. 

[misterc9]

Maybe a weak valve spring.  You could test it on the car by trying to push the valve open with a bar then noting the pressure difference between the two valves on the bad cylinder. Make sure that the piston is down and both valves are closed. You might have to take the pushrods out to do this. Pfitz's  timing light idea is good too.

Edited July 3, 2020 by misterc9 (see edit history)

[Stude17]

I suspect that your problem with No 2 cylinder is in the valve train.  Other than tight valve clearance could the exhaust rocker arm be binding on the shaft?

[edinmass]

18 minutes ago, Stude17 said:

I suspect that your problem with No 2 cylinder is in the valve train.  Other than tight valve clearance could the exhaust rocker arm be binding on the shaft?

Read his first post, valves, rockers, cam, and compression are fine. It’s spark or mixture........lean burn misfire is the most likely candidate when nothing seems to be wrong.

[jan arnett (2)]

15 hours ago, Studeous said:

This is a case for Gus....

How many young people know who gus was.

[Guest]

Gus was a great mechanic but Mimi was more interesting.

[carbking]

Thinking out loud (dangerous).

 

It has been a long time since I had a Cadillac tripower intake to look at, and memory sometimes has a parity error

 

I have had, and still have a number of Cadillac dual quad intakes. These are notorious for cracking. On the dual quads, there is a steel tube pressed through the heat cross-over to provide an air source for the heated air for the automatic chokes. From memory, every one I have ever had was cracked where the tube was pressed through. We would magniflux, and sure enough, there is the crack. My welding looks like the underside of my third grade desk, but used to have them professionally welded.

 

What would be the ramifications of an internal exhaust leak? Could this cause a leak mixture in one cylinder?

 

Like I said earlier, I no longer have a Cadillac tripower manifold to check.

 

Jon.

[Bloo]

1 hour ago, carbking said:

What would be the ramifications of an internal exhaust leak? Could this cause a leak mixture in one cylinder?

 

In my line of work we called that a "dilution misfire". It isn't lean because the exhaust is more or less inert, but it still misses. It is exactly what you get when an EGR valve on a newer car doesn't quite seal. The exhaust doesn't mix because the engine RPM is low, and the exhaust all winds up in one or 2 cylinders, killing them. CO will be close to normal on the exhaust analyzer, indicating a more or less normal mixture, but the HC output will be through the roof because of the miss.

[edinmass]

I agree, an egr or a cross over exhaust leak bleeding an inert gas into the combustion chamber causing a misfire due to stoichiometric imbalance. My guess was lean burn misfire........due to the fact 99 percent of what I work on the last 25 years couldn’t bleed exhaust into the intake.............same issue, just a different type of mixture problem. That’s why a five gas machine or an oscilloscope are so handy........when the problems separate the men from the boys..............

[Bloo]

The exhaust thing didn't occur to me either, even though I drive a flathead Pontiac, and they are prone to it. I am still betting it will be a lean misfire. We don't yet know whether it has idle jets on the outside carbs, and if it is progressive or fixed. That makes it hard to guess.

[Matt Harwood]

We played with it more today. One, the plug wire will fire a timing light and a spark tester, so I have to believe that plug is firing. So that means fuel is the problem.

The center carb is the only one with an idle circuit and does most of the work of actually moving the car, and oddly enough, the outer carbs are vacuum actuated like the vacuum secondaries on a 4-barrel. 

 

We checked for vacuum leaks and there's nothing obvious that's easy to see. We experimented with propane to see if it was inhaling anywhere it shouldn't and there was no change to the idle--it doesn't seem to have an external vacuum leak. However, now that I'm thinking about it, it may be possible that there's a vacuum leak in one of the carburetors that isn't manifesting itself in an obvious way. I don't know.

 

I don't believe this engine has an EGR so exhaust gasses are probably not getting mixed with the intake charge, unless perhaps there's an exhaust crossover under the carbs. That may be leaking, but I have to imagine it would affect all the cylinders since it's just 2 barrels feeding all 8. That's really the weird thing: we have 7 healthy cylinders and one dead one with nothing obviously amiss.

 

I do think our next step is to take it to my friend with a 5-gas analyzer and let him have at it. He's a brilliant mechanic and diagnostician so I guess we'll let him have a shot at it. I'll definitely update what we find--maybe some wagers can take place before then...

 

 

Edited July 4, 2020 by Matt Harwood (see edit history)

[edinmass]

Ok........so here is why I won’t wager. As a profession mechanic and a diagnostic technician, I NEVER, EVER, take anyone’s thoughts, assumptions, opinions, or word that every thing they checked on is “ok”. I always start from step one, and go through everything myself. Since  Matt has been around the block, I would go at this problem differently in person. First, I would check the mechanicals.........valves, compression, leak down, wet and dry. I would do this to prove it’s not a mechanical issue first. Then, I would examine theignition system in its entirety.......primary and secondary..........including checking KV’s at the plug with a scope. Then, I would continue on to fuel. In this case, I would be willing to pull the intake to check on the system, in order to understand it. What ever it is, it’s not a quick easy fix. If I couldn’t prove every part of the ignition system perfect, I would not pull the intake. Sometime you just have to dig in and pull things apart. All it is is time and money...........which is what it always comes down to.

Edited July 4, 2020 by edinmass (see edit history)

[Bloo]

2 hours ago, Matt Harwood said:

The center carb is the only one with an idle circuit and does most of the work of actually moving the car, and oddly enough, the outer carbs are vacuum actuated like the vacuum secondaries on a 4-barrel. 

 

The implication of that (no idle jets and progressive actuation) is that the throttle plates on those outer carbs have to seal when closed. I would really wonder about the "barrel" closest (well.... closest in runner length, however that works out) to the missing cylinder. Could it have a bad throttle shaft or an egg shaped plate or something?

 

2 hours ago, Matt Harwood said:

I don't believe this engine has an EGR so exhaust gasses are probably not getting mixed with the intake charge, unless perhaps there's an exhaust crossover under the carbs.

 

No EGR. That came up because Carbking remembered seeing cracks in some caddy manifolds that could potentially leak air or exhaust to the intake. The behavior would be like malfunctioning EGR if it were exhaust.

 

 

 

Edited July 4, 2020 by Bloo (see edit history)

[F&J]

10 hours ago, Matt Harwood said:

We played with it more today. One, the plug wire will fire a timing light and a spark tester, so I have to believe that plug is firing. So that means fuel is the problem.

I've been following along since post 1.  

 

I have to agree with every part of Ed's last reply.   Go back and read his thought train on this very unusual problem.

 

10 years ago I was asked by an upscale resto shop to help with the same exact symptoms on a stock twin carb 1958 Porsche 356.  The top mechanic there who also was a life long race engine guru, worked with me at that shop.  We went through all of what has been done to this Caddy, and still had a cylinder on the right bank that simply would not "fire"..

 

I simply cannot recall what I found after pulling the engine and bringing it to my place for pulling that right head, but it was mechanical, not ignition, fuel, or vac leak, etc.  I am positive I did not replace the head, but I tend to think it was something very "untypical", like a walking valve seat. 

 

My point is that I agree with Ed on working with a totally open mind, as far as dealing with a very odd issue like this one also seems to be.

    

[Frank DuVal]

On 7/3/2020 at 10:07 PM, Matt Harwood said:

I don't believe this engine has an EGR so exhaust gasses are probably not getting mixed with the intake charge, unless perhaps there's an exhaust crossover under the carbs.

 

I have not seen a stock V-8 intake manifold of the mid 50s through the 60s that did not have an exhaust crossover! It is why there is a manifold heat riser valve, to force the exhaust through the intake manifold passage to heat the carburetor on cold start. Not saying they do not exist, just I have not seen a stock intake without the passage.

 

A crack in that passage will act just like a leaking EGR valve on a modern engine.😉

[Bloo]

Yes, and its been going on longer than that. Literally everything with a downdraft carburetor (or throttle body injection) has a hotspot under the carb (or TBI). Sometimes its coolant instead of exhaust, but it is always there. Maybe there could be exceptions on racing homologation specials and the like. You won't see it on cars intended to be street driven.

Edited July 5, 2020 by Bloo (see edit history)

[edinmass]

Matt........”the plug wire will fire the timing light and spark tester so I believe the plug is firing” is not a definitive positive indicator of good spark. You need to know voltage and burn time. An analog oscilloscope would be helpful, but a digital one with comparative graphing would be better. The frustrating part of these weird and difficult problems is special equipment you use once every 18 months in small shops. Back when I had my big shop, I ran seven full time “A” technicians, and we were one of the specialized IM240 emission testing and repair stations. The minimum investment to get a shop to certification was well over 200k (in 1995 dollars) in tools and equipment. We used a chassis dyne and it was a fantastic tool.........running the car under and simulated road profile to locate noise, vibration, and running problems. Usually we could cut to the chase on a difficult car in under 45 minutes. We routinely serviced over 1000 cars per month. When doing that many cars you get good quickly just from repetition. I always took the “hard cases” as my flat rate guys would toss up their hands if it wasn’t an easy fix..........over time I became friends with the best Automotive Technician in the country.......and I mean THE BEST. Under his tutelage I learned and advanced my skill set by light years. Two years ago, I was speaking to one of the top executives at GM on the field at Pebble. We were working on a running problem, and we got it figured out in under ten minutes after the shop had over 80 hours in it. The guy complemented me, and commented he knew a guy who would have also fixed it that fast..........and he said “Gary” was the best. I agreed with him and explained I have spent hundreds of hours in classrooms and shop time with him....I said I’m a Gary Protégé.......he gave me a big smile. There a only a few “brilliant” and gifted technicians in the US.(I consider my skill set at half of “Gary’s”) I have met and worked with two of the top ten........and learned an incredible amount from them. The most important thing when it comes to repairing cars...........have a good, logical diagnostic routine, take nothing for granted, start with the basics, and prove every part of the cars system as “perfect” or fail. There is NO good enough. And the final and possibly most important thing......enjoy the challenge, don’t get frustrated, and NEVER, EVER give up.

Edited July 5, 2020 by edinmass (see edit history)

[m-mman]

On 7/5/2020 at 5:10 AM, edinmass said:

over time I became friends with the best Automotive Technician in the country.......and I mean THE BEST. Under his tutelage I learned and advanced my skill set by light years.

 

On 7/5/2020 at 5:10 AM, edinmass said:

he said “Gary” was the best. I agreed with him and explained I have spent hundreds of hours in classrooms and shop time with him....I said I’m a Gary Protégé.

 

I wondered where you learned what you know! 

For whatever reason so little auto repair is TAUGHT in a formal curriculum type of environment.  Maybe some high school auto shop (years ago) but I think most mechanics have learned through trial, error and having somebody insisting (guessing) what the problem is and then trying it. No theory. No understanding of design and operation. 

 

On 7/5/2020 at 5:10 AM, edinmass said:

And the final and possibly most important thing......enjoy the challenge, don’t get frustrated, and NEVER, EVER give up.

 

Ok, Ed. maybe you can give us your favorite tips for avoiding frustration, extreme anger and just walking away. . . . .

Staying with it, keep evaluating, maintaining the process of elimination, and KEEPING INTERESTED is a very difficult thing to do.

It can be psychologically painful. How do you do it? 

 

[Matt Harwood]

More diagnostics today. A little propane didn't seem to do much when moving the wand around the engine, but I'm still not ruling out a vacuum leak. My current theory is that the intake manifold gasket is bad and it's sucking air from down low, under the manifold where we can't reach it with the wand. I want to drive the car and see if that cylinder starts to fire at higher throttle openings when there's less vacuum--it won't suck ambient air if vacuum is low and it's easier to pull through the carb. Not sure how I will be able to measure anything if I'm driving. Exhaust temperature readings might be useful, but I'm not positive that exhaust port for cylinder #2 will not be heated by the other cylinders' exhaust after a drive. Maybe it'll cool off faster at idle if it's just pumping air...

 

My other thought is to simply dribble some extra fuel down the carburetor throat that feeds that port at like 2500 RPM. The idea is to get it to run pig rich and perhaps cylinder #2 will start firing with all that extra fuel in there to match the extra air. 

 

Replacing intake manifold gaskets doesn't look like a terrible job on this car, but I don't want to tear into it unless we have to. Tomorrow we'll try a few more experiments before calling in the guys with the expensive equipment.

[edinmass]

17 minutes ago, m-mman said:

 

Ok, Ed. maybe you can give us your favorite tips for avoiding frustration, extreme anger and just walking away. . . . .

Staying with it, keep evaluating, maintaining the process of elimination, and KEEPING INTERESTED is a very difficult thing to do.

It can be psychologically painful. How do you do it? 

 

First off, no good or great technician gets there by himself. It’s a learned skill. The trick is listening, watching, and knowing who really is talented versus people who think they are but can’t fix their way out of a paper bag. First off, you need 3000 hours in a shop spinning wrenches to become decent. You can become a good parts changer in about 1000 hours. Knowing how to use sophisticated test equipment is a plus.......plugging in a code reader and expecting to fix a car because it has a map sensor or O2 sensor code and swapping out a part is NOT fixing or diagnosing the problem. A car can toss a code for many reasons.........sure, a lean code on an O2 could be a bad sensor, and it also can be a vacuum leak, and electrical short, bad injector, a ground problem, the list is endless. Understanding how a sensor works, and what input and output it performs and how it modifies fuel trim is crucial. You just can’t learn this stuff in a year or two. Everyone thinks old cars are easy to fix........not much to them. It’s amazing that 99 percent of pre war cars run rather poorly, and are not set up well in regards to the chassis. When new, cars built post 1914 are generally pretty decent. It’s amazing how good most cars preform after we spend a few weeks sorting them out. Cars that I didn’t think too much of more often than not surprise me how well they function and drive when you consider their price category. 
 

How not to have a car drive you insane? Another learned process. I enjoy the difficult problems that have been to half a dozen other shops. Fixing something that others tried to and failed is very rewarding to me. The challenge is similar to climbing a mountain, running a marathon, and other similar challenges............I have NO desire to perform routine maintenance on any car. I have been doing this a LONG time.....and I’m still learning new things every month. Recently I spent an afternoon with a 80 year old guy who’s shop is still going strong. He only does custom springs for cars and trucks. I had a problem, and knew I needed someone with a lifetime of experience to solve the issue I was having. The problem was how to get him to spend five hours with me explaining what I wanted to know. Basically 65 years of insight and experience in just a few hours. I managed to get the time I needed with him. He didn’t charge me a dime. What I did do was give him a ride in a Model J a fair trade for both of us. Got my problem solved, got a tour of an interesting shop, and now I think I have a much better understanding of springs than I did before. 

[joe_padavano]

On 7/5/2020 at 12:30 AM, Frank DuVal said:

 

I have not seen a stock V-8 intake manifold of the mid 50s through the 60s that did not have an exhaust crossover! It is why there is a manifold heat riser valve, to force the exhaust through the intake manifold passage to heat the carburetor on cold start. Not saying they do not exist, just I have not seen a stock intake without the passage.

 

A crack in that passage will act just like a leaking EGR valve on a modern engine.😉

 

True, but the #2 runner (upper LH port in this photo) is about as far away from the exhaust crossover as possible. Any such crack would more immediately effect cylinders closer to the center of the engine.  And yes, that port shares runners that are routed above the crossover, but again, how is it that the cylinder furthest away from this theorized crack is the only one impacted by it?

 

 

A vacuum leak right at that corner of the intake would be more plausible, but still I have a hard time understanding how a leak bad enough to kill that cylinder doesn't also result in an engine that runs extremely poorly. Note that the intake does not have any vacuum ports in that specific runner. In any case, Matt's propane test would have detected such a leak.

 

If an ignition scope hasn't been tried yet, I'd suggest that.

 

And for Frank's benefit, here's a 1960s intake that does not incorporate an exhaust crossover. This is from the BOP (plus Rover) aluminum 215 engine. 😉

 

[edinmass]

Matt....I just realized you didn't mention if you checked the filter on the plug wire..........just thinking out loud. 😁

[FLYER15015]

NOW THAT'S FUNNY !!!!!!!!

I did not know Honda's had those.

I NEVER cleaned the one on my Honda 90, when I had one years ago.

 

Mike in Colorado

[edinmass]

3 hours ago, FLYER15015 said:

NOW THAT'S FUNNY !!!!!!!!

I did not know Honda's had those.

I NEVER cleaned the one on my Honda 90, when I had one years ago.

 

Mike in Colorado

 

 

I still have my CT-90 up north. My driveway is VERY long, so we use it to get the mail when its cold outside when we don't want to take the ten minute walk. 

[auburnseeker]

I have bounced this problem around wit ha Friend that built race engines for years and worked at Cadillac as a field engineer fixing Problems that the normal guys couldn't.   I get to hear lots of stories when he stops by for "the Old man's club" as my wife calls it.

He read some of the thread at one point as well to get a little background on what has happened.  He said a problem he's seen before is a weak Valve spring (might have gotten overheated at some point) can cause a similar situation.  It won't show in a leak down of course because the valve is forced closed but doesn't function properly when running.  It would be fairly easy to check if the Valve cover on that side is easy to get off.  

Not sure if this was covered yet,  but atleast something to rule out. 

[edinmass]

Just now, edinmass said:

Randy, I thought about a bad spring......but how would only one get overheated? Another possibility is to pull the two rockers on that hole, and do a five gas test, thus eliminating the possibility it’s another hole, and not the one they are looking at. That’s why I posted that if I were working on it, I would start looking at the mechanical Condition first, ignition seconded , and fuel last. I still have a hunch it’s a bad intake. Looking forward to them fixing it, and posting photos of the problem. Learning from people’s hard problems always adds to ones skill set. 
 

PS- how is the Auburn? PM me with updates as not to hijack the thread.

 

[auburnseeker]

6 minutes ago, edinmass said:

 

Not sure how it would only be one overheated.  Could be broken but not completely through so it's weakened.  I know I broke one in my 48 Plymouth.  As you mentioned best not to leave anything unchecked.  Engine could have been apart at some time in the past and something used substituted or was marginal so they didn't replace it.  Who knows with all the hands that have been on these cars over the years.  Easy enough to check without any fancy equipment. 

I'll Pm you on Victoria.

[Matt Harwood]

We've got the valve cover off and had it running. Valves are moving correctly, both at idle and at about 2500 RPM. 

 

We're going to pull the intake and see what's going on under there. My guess is that the gasket has failed or the intake casting is flawed somehow. 

[edinmass]

[auburnseeker]

I would still try compressing those springs while you have the cover off,  then you will know for sure. Could be just enough that it's hard to see with the naked eye even when running. No reason to not do it at this phase with it apart. 

Eventually you'll get it figured out and will know exactly what to check when the next one comes in with the same problem.  

[PFitz]

35 minutes ago, auburnseeker said:

I would still try compressing those springs while you have the cover off,  then you will know for sure. Could be just enough that it's hard to see with the naked eye even when running. No reason to not do it at this phase with it apart. 

Eventually you'll get it figured out and will know exactly what to check when the next one comes in with the same problem.  

Another test.  Use the timing light to "strobe" the valves/rocker arms. An inductive timing light pointed at each valve and spring - with shop lights out - should show the valve and spring in the same position for each flash of the light. If they seem to change position, there's a problem somewhere in that valve train.  

 

Paul

[F&J]

16 hours ago, Matt Harwood said:

We're going to pull the intake and see what's going on under there. My guess is that the gasket has failed or the intake casting is flawed somehow

I think you posted earlier that the cylinder would not fire "at any speed".  And somebody here also said something like: ..if a vacuum leak could kill a cylinder at high rpm's, it would have to be a huge leak..and therefore the engine could not possibly idle.

 

Looking forward to what you do find on this car.  it's a tough one.