The Stovebolt Site Forums The Shop Area Engine Shop Runs Rough - Compression?

I'v gotten my '53 GMC 228 to run (very roughly and at high idle). I've been tuning things up, dinking around with the points, timing, advance, and the mixture needle, but I was still getting some backfiring and burping no matter what. Finally, I started her up, walked around to the passenger side, and decided to pull a plug wire while the engine was running. I randomly grabbed a plug wire and pulled it off. Lo and behold - no more roughness, no more explosions! I hopped back in and throttled down all the way, and the engine still kept running nice and smooth. It was a lovely sound!! When I tried her cold the next day, with the plug still off, the engine almost caught, but wouldn't start.

Is this a compression problem?
I think I'll get a set of plugs and cables just to make sure they are not the problem.

GMC53,

I would think it is a head gasket issue, or a firing order issue.


I guess you could call it a compression issue if the head gasket was blown between cylinders...not uncommon.

Do your compression test, but also verify your plug wire location/firing order.


Stuart

GMC -Have you checked for manifold gasket leaks? If they are leaking an engine will miss. Another possibility might be a blown head gasket but the compression check would detect that Also a stopped up fuel line or clogged carb will make them run rough!Check your distributorn cap for cracks as thatis another possibility. Be sure your firing order is correct as a couple of crossed wires really makes them run awful... Good hunting..

I finally got back out to the garage and put in new spark plugs and a new manifold gasket. I checked the wire order (it was right) and started the engine. It ran rough, so I got out and pulled the #4 wire again. Right away the engine smoothed out and I throttled down. Every time I touched the wire to the plug the engine coughed or backfired, so I left it off. The engine was running nicely enough that I put it in gear and drove forward and backwards a couple of times (First Movement under Power!) So that's good.
After I shut down I noticed the exhaust pipe coming out of the manifold assembly was very loose and there were a few rust holes in the muffler. Also there is no tail pipe past the muffler. Could this be part of the #4 cylinder problem, or do I still need to check out the compression? I'm hoping to drive the beast over to a nearby mechanic and let him do a check up.

GMC53,

It sure sounds like a blown head gasket to me.

I would run the firing order on the wires ONE more time just to make sure. Be sure to go with the proper rotation of the distributor.

In a clockwise rotation you would want 153624 as your order.

I don't think your exhaust pipe or muffler problems would have a bearing on this.

Stuart

You could also have a sticky valve on #4.

I was also thinking sticky valve on #4. You'd think if the wires were stuck in there rong (firing order) the engine wouldn't run right as it would just back fire.

However..what about cross fire? Do you have all new plug wires, cap, rotor? If a neighbor cylinder was trigging that cylinder too (on the distributor) that could cause issues. Old stinky wires could cause that problem.

Here is an update:
After all my work trying out options and suggestions, I finally had the truck towed to a nearby, recommended garage (Parents, in S.W. Mpls) and Dan took a look. Turned out the compression is fine. The problem turned out to be that the plastic knob for the primary terminal on the side of the distributor had been overtightened in the past and broken off. I had put two nuts over the small threaded bolt as spacers. They were grounding to the distrib. He removed them and cut a piece of PVC tubing to use instead. I went to pick it up tonight and it started right up! My son and I had an exciting 2 mile drive back to our house (no fenders, box, grill, speedometer, or signal lights of any kind) but no problems! Dan did discover that the distributor shaft is bent and I will need to replace that before I do a lot of driving. Thanks to everyone who has had the patience and expertise to help me work through my various postings.

Craig, GMC53

GMC53,

That is a most bizarre finding. I guess you learn something new every day.


Stuart

sounds like a bad valve.......