Rough engine (with pics)

I am trying to finish my first engine rebuild, and am almost there, save a few details. This is an even fire Buick 231, from about 1980. However, my engine is running really rough, almost sounds like it is missing a cylinder, and I have to set the idle very high to get it to idle. I think it has a vacuum leak or mis-run line. I’m almost positive all cylinders are firing properly. I have a new distributor; the cap is in good condition, new plug wires, and new plugs. I have checked to make sure I have spark on all cylinders, and I do. A compression test came back with no cylinders under 91 psi, so my valvetrain should be good. I have toyed with the mixture on both sides of the 2 barrel carb, and the idle, and believe it is set somewhat correctly. It is hard to tell with it running so rough. I think my trouble is related to how my vacuum lines are setup. I don’t really know what all these extra lines are for, and where they go. The dash has a vacuum gauge, what should this show under normal idle? I took some pictures of items I don’t really understand.

http://web.ics.purdue.edu/~herbertd/Jeep/8.htm

General pics are at the link in my signature.

Thanks for your help, I am so close to being able to finally drive this thing after 3 months of working on it almost every single day.

 

WOW! Where to begin? Here are my Observations based on what you said and the pics...
1. a cylinder with around 91 PSI of compression is almost a dead cylinder. They should all be up above 135 to run well, and a 'good' engine will have 150 to 160 each.
2. the vacuum gauge can be a good diagnostiv tool for several reasons, but basically if your engine is in good shape, and running properly with correct timing, 18 to 22 inches of vacuum is probably a good ballpark figure.
3. the vacuum line coming off the front of the carb should run to the vacuum advance on the distributor.
4. the UFO shaped object on the rear on the intake manifold is an EGR valve. (exhaust gas recirculation) it needs to be hooked up, but not to a constant vacuum source, and the engine can run without it.

My guess is that your EGR valve is hooked up to constant vacuum and that is causing a rough idle. when the valve is open, exhaust is rerouted into the intake manifold and at idle it will all but kill an engine. Unhook it and see what happens. be sure to plug up the vacuum source or that will be the source of another vacuum leak.
Then there is your compression. I cant tell you for sure without seeing all the cylinder compression readings, but 91lbs is bad. This can be caused by a number of things that are difficult to diagnose over email.
If one cylinder is low, that can be several things, broken rings, burnt valve etc.
If two adjacent cylinders are low, I may suspect a cylinder head gasket thats bad.
If theyre all down and its a fresh engine, valve timing could be the culprit. tell us what all the cylinders read, and list the cylinder number when doing it and I may be able to help more.
in the beginning of your post you eluded to rebuilding this engine. What did this entail?
Hopefully this can help, but if not give me some more info and maybe I can help out some more.
Brannon

 

The first picture is the EGR valve. It should be connected to carburetor (ported) vacuum via a ported vacuum switch. The ported vacuum switch disconnects the carburetor vacuum from the EGR valve when the engine is cold. Carburetor vacuum comes from a port in the venturi just below the throttle plate. When the car is idling (fuel coming from the carb idle circuit) the throttle plate is closed and there is no carburetor vacuum. The EGR valve mixes exhaust gas with the fuel-air mixture to reduce the combustion chamber temperature and minimize NOx emissions. When the car is idling or cold, there should be no exhaust gas coming through the EGR valve. As the (warm) engine speeds up, the carburetor vacuum increases, and the exhaust gas is mixed in.

The EGR valve often has carbon buildup on the pintle (the post that sticks into the manifold to block the exhaust gas) and then sticks open. This will cause a rough idle. If everything is working right, you should be able to pull the vacuum hose off the EGR valve when the engine is cold, and feel no vacuum as you rev the engine. As the engine warms up. you should be able to see/feel the diaphragm of the EGR valve move as you rev the engine and carb vacuum comes up. In this case, I'd just get an EGR gasket, remove the EGR valve, wire brush the pintle, make sure the pintle moves, and reinstall with a new gasket.

 

Just wanted to toss out a couple of thoughts. I just finished putting in new rings in my F134 on a 56 Willys CJ5 . It was an in-frame ring job. (I did not remove the motor.) She barley started and ran poorly when I first started her up. And after about 5 miles she smoothed out some. She also smoked for about the first 10 mins. of running. Then the smoke went away. :&gt

Being a new rebuild, I would guess your rings have not set yet. And that could be the reason for low compression. Or maybe your compression gauge is off. I really would not be too concerned about it till you have driven it a few miles.


Also I was also real radical with steam cleaning my engine. Due to this, I got a lot of moisture in my distributor and my points seemed very corroded. I filed them down with a emery board. ( The wife keeps me in regular supply :&gt and afterward the motor fired up quickly and ran like new. I now just bump the starter and she fires right up. If you have the old points and condenser on your motor, might be something to double check.



I am not a professional mechanic. Just a fairly good shade tree type, who keeps trying stuff until something works, or I screw it up real good. Frankly I find working on my jeep to be as much fun as driving it. Guess I love the challenge of identifying a problem and then fixing it. I probably spend 3 times as long as a real pro would on repairing something. But I try to do it my self.

Let us know how you come out.


Cliff Todd

 

I think I finally found the problem. The intake manifold gasket is just a little bit the wrong cut, so there was not a good seal between intake and heads. With plenty of gas flowing, it ran better, because the fuel counterbalanced all the extra air, but at idle, it was enough of a leak to cause a loss of vacuum. I finally found this by reving the thing up, and spraying carb cleaner all over the place, till finally I sprayed it somewhere that caused the engine to rev more. The intake manifold gasket I had on there was for a 1980 and up 231, and it looks to be wrong, but not by much, so I ordered one for a 1978-1979 231. I don't know exactly what year my engine is, so I hope this makes the differance.