What's the best way to find a dead cylinder?

-
IMG_5894.gif
 
I had something going on with my 383 what you’re describing, found out it was a couple bent pushrods
 
TF360 said:
You mentioned that it runs like it has a dead cylinder. What does that mean? No power? Can you describe the symptoms a little more?
Click to expand...
On cold start, the engine goes to high idle like it should, but has a misfire sound from the exhaust pipe. The engine also shakes a bit. When kicked down to curb idle, it idles rough and the engine shakes as if it isn't hitting on all six. When stopped at a red light in gear, the idle is very slow and rough. Idle speed in neutral is set to 750 RPM.
 
Sounds electrical or fuel related. How's your fuel system Cruiser? I recently had to replace the Tank on my 74 Duster because sediment and rust particles were coming through. Make sure all the simple stuff is ok - Cap, Rotor, Distributer. Maybe a bad plug firing intermittently?
 
Put a vacuum gauge on it.. report back here with the manifold vacuum at idle, and observations of what the vacuum gauge needle is doing (steady, quivering, bouncing?)

Most likely it is something simple.. and it all needs to be checked before assuming the worst case...

A picture of all the plugs could help illuminate an issue... a compression test, checking the valve lash... if it has a mechanical cam and lifters..

Also where is the curb idle timing set at? Did this problem just crop up, or is it in part, why you rebuilt the carb?
 
I am not going to re-type what I said in post #15, it is all correct & the quickest way to start the trouble shooting process of isolating the problem. Short out each cyl one at a time, & you get an rpm drop. If rpm drop is about the same for ea cyl, you have a common problem across all cyls. If one cyl has a noticeably larger rpm drop, then that cyl needs looking at, possibilities in post #15.
 
Fire it up cold, immediately coat the exhaust manifold in windex up where each leg joins the cylinder head, observe. You can respray it if it's slow to warm up.

Any cylinder that is slow to heat up will be obvious (still wet), and the thermal shock will not be an issue on a cold manifold.
 
TF360 said:
Sounds electrical or fuel related. How's your fuel system Cruiser? I recently had to replace the Tank on my 74 Duster because sediment and rust particles were coming through. Make sure all the simple stuff is ok - Cap, Rotor, Distributer. Maybe a bad plug firing intermittently?
Click to expand...
The car has a new tank and fuel filter, plugs, rotor and distributor cap. Valve lash is set correctly.
 
I remember you were fooling around with the gasket at the base of the Carb. No vacuum leak there huh? Does #5 plug looks a little different in the pic anyway
 
Get a set of Autolites made for the Slant and put them in there. Maybe you'll get lucky
 
Plugs look ok, and don't show anything obvious.

What is the initial timing set at, and do you have a vacuum gauge to hook up to manifold vacuum?
 
cruiser said:
On cold start, the engine goes to high idle like it should, but has a misfire sound from the exhaust pipe. The engine also shakes a bit. When kicked down to curb idle, it idles rough and the engine shakes as if it isn't hitting on all six. When stopped at a red light in gear, the idle is very slow and rough. Idle speed in neutral is set to 750 RPM.
Click to expand...
Sounds and looks like a burned exhaust valve because you hear it at the tail pipe and judging from the plugs looks like 1 and 6 are your culprits. Time for a compression and a leak down test.
 
chryslercruiser said:
Plugs look ok, and don't show anything obvious.
Click to expand...

Not to me. # 1 and #6 do not look normal. Something going on in those holes. Burnt valves high on the list of suspects IMO. A leak down test would reveal that. Buy a tester, best tool I ever bought as far as diagnostic.
 
I thought he recently had the head off of that engine? And earlier it was said "all cylinders had the same rpm drop when plug wire pulled vs the others...
 
volaredon said:
I thought he recently had the head off of that engine? And earlier it was said "all cylinders had the same rpm drop when plug wire pulled vs the others...
Click to expand...

And? It is running fine? Not according to the OP. Leak down test that motor IMO.
 
DC 340 said:
Not to me. # 1 and #6 do not look normal. Something going on in those holes. Burnt valves high on the list of suspects IMO. A leak down test would reveal that. Buy a tester, best tool I ever bought as far as diagnostic.
Click to expand...

I don't believe it is abnormal for a slant six to have cylinders 1&6 running richer than the others... some intake manifolds were significantly worse in this regard than others... and 1974 was not one of the good ones...

Yeah the plugs are not great, but they are not the issue...they are just reporting a rich condition, and this was discussed last week or so...

I'm thinking a vacuum gauge will tell us more... and maybe a better carb than the 1945 Holley carb from the same year will solve all of the problems? I have a 1945 and I have futzed with it plenty. I look forward to the day I put a better carb on, tho the 1945 I have is a truck carb, and a few years later.. so not quite as bad as the early 70's stuff.
 
i'm gonna guess that #5 is your problem.

ain't got but a bit of blush on her, which makes me think you might maybe be missing the suck part of the squeeze, bang and blow funtimes super party.

time for compression + and a leak down test.
 
I see you're on another thread asking about crate engines. Have you EVEN run a compression test yet?
 
RustyRatRod said:
I see you're on another thread asking about crate engines. Have you EVEN run a compression test yet?
Click to expand...
Good question. The answer is no, not yet. Here's what I'm thinking. The motor in my Duster was a replacement engine installed 36 years ago, and now has over 105K miles on it. I'm not sure how much life this engine has left in it. I suspect that it had poor maintenance prior to my ownership. If I can solve the problem I currently have, there's no guarantee that another problem won't pop up shortly thereafter. I plan on keeping this car forever and driving it a lot. There's one school of thought that says to cut your losses and just go with a new engine. That way you can enjoy many years of trouble free driving. Since the current engine now in my car isn't the numbers matching original, it's not that valuable. If it WAS the numbers matching motor, no question - I'd keep it and rebuild it. But this isn't the case unfortunately. Yes, I'm planning on running the test you mentioned, and I really appreciate the technical advice. I just don't want to "throw good money after bad" as the old saying goes. I definitely haven't made the decision to buy a new motor. I'm just in the "thinking about it" phase right now. There's a place called S and J Motors that will sell a rebuilt long engine, balanced and with mild head porting work for about 3K. What's your take on all this, Rusty?
 
[1] #5 plug is whiter, could be coolant leaking into that cyl.
[2] Hooking up a vac gauge. Disconnect the PCV & use that port. Temporarily increase idle rpm to where it was.
 
cruiser said:
Good question. The answer is no, not yet. Here's what I'm thinking. The motor in my Duster was a replacement engine installed 36 years ago, and now has over 105K miles on it. I'm not sure how much life this engine has left in it. I suspect that it had poor maintenance prior to my ownership. If I can solve the problem I currently have, there's no guarantee that another problem won't pop up shortly thereafter. I plan on keeping this car forever and driving it a lot. There's one school of thought that says to cut your losses and just go with a new engine. That way you can enjoy many years of trouble free driving. Since the current engine now in my car isn't the numbers matching original, it's not that valuable. If it WAS the numbers matching motor, no question - I'd keep it and rebuild it. But this isn't the case unfortunately. Yes, I'm planning on running the test you mentioned, and I really appreciate the technical advice. I just don't want to "throw good money after bad" as the old saying goes. I definitely haven't made the decision to buy a new motor. I'm just in the "thinking about it" phase right now. There's a place called S and J Motors that will sell a rebuilt long engine, balanced and with mild head porting work for about 3K. What's your take on all this, Rusty?
Click to expand...
I think you're on the right track. Regarding the "crate engine" approach. If you plan to start with nothing, in other words, you want a "TOTALLY" complete new engine, just be advised it will not be cheap. Someone will have to come up with an entire long block. That's the easy part. Then, they have to locate all of the tin, the valve cover, timing cover and oil pan. Next is all of the various fasteners. That takes a lot of time and effort. It's not something that's going to happen for say 2500-3500 dollars. Sure, a basic long block can be had for that, but people seem to forget about all the other details. That is of course you plan on using all of that from your present engine. If you want a "plug and play" approach, just be prepared to pay someone for their time, parts and effort.
 
You must log in or register to reply here.
-

Back
Top