Rough running engine...something bent??

[jeepthing]

I've only had my 91 GW for about 2 months or so now, and since then I've done the TFI upgrade, changed the carb for a rebuilt one, fuel filter, wires, etc. It always had a VERY rough idle, and with the new carb seemed to help quite a bit, but the roughness is still there. I've mentioned before here that cylinder #4 fouls the plug,and my compression in there is 96 while the ohters are around 150+. I'm not sure if my roughness is caused by that cylinder and its associated problems or not.

I'm starting to think I may have another problem causing this roughness. When I first bought it, after getting it home, only then did I notice that the fan blade had one of the blades sheared off about halfway up. Looks like it hit something and broke off. I've also noticed after checking other things that it might have been involved in an accident in the front end...as the hood appears to be from an earlier model, and the grill bolts don't all line up. Here's what I'm thinking...it was in an accident while driving, pushed in the front enough to contact the fan blade, and broke it. Not sure what it would do as far as bending something so that I would be wobbling now? Broken motor mounts??? The radiator also looks like it has been replaced.

So, first off, for those with smooth running 360's, if you remove spark plug number four does it get pretty rough at idle? If so, then it must be my cylinder problem...otherwise maybe something has been wacked and now it makes the engine wobble.

Sorry for the long post, but I've got to figure out this problem.

(Incidently, forgot to mention that I've already replaced the broken fan...just the fan, not the clutch)

[wagontrain]

First of all the "engine wobbling." Do you mean that the entire engine shakes in the engine bay?

I hate to try to diagnose a problem like this long distance becasue a rough idle situation can be caused by so many things. However, a V-8 engine shouldn't idle that rough with one dead cylinder, so your idle problem probably lies elsewhere.

But if you have 7 cylinders consistantly pushing 150+ psi, and one at less than 100, you definitely have an internal problem that needs to be corrected ASAP. It could be a burnt or bent valve, broken spring, cracked head, cracked piston, or cracked cylinder wall; maybe something else I'm forgetting right now.

I'd look for vaccuum leaks first. Get a can of carb spray and spray it all around the carb base, vaccuum connections, intake gaskets, and especially the EGR valve. If the idle speed changes when you spray it on a certain spot you've found a leak. If it's bad enough, it could cause a very serious idle problem.

On a side note - Which Accell wires do you have? If you have the yellow ones, get rid of them. I sold auto parts for 15 years; the "el cheapo" store brand wires are much better than the Accell yellows. Not that this is causing your problem; just trying to pass along a lesson learned the hard way.

[91 TANK]

I had a similar problem and it was vaccum related. It turned out to be the master cylinder had a leak. $250.00 later the engine is a smooth as silk. I believe that the master has the hose going back to the third cylinder.

[Panoscopic]

Sounds exactly like mine. I've been looking for the vacume leak FOREVER. I hate it because otherwise, the engine is smooth nice to drive.

[andy d]

replace that fan fast. you really dont want to lose another blade.