Puff/Miss in exhaust.

[SoCalSlaughter]

I noticed recently, my 1990 Suburban 5.7 has a slight puff or miss in the exhaust at idle. Its not consistant, might puff 3 times in a row, stop for a second, puff once then start missing/puffing again. I did a compression test and all cylinders where between 145 to 150 psi. I dont notice a performance difference. I guess its just annoying haha Any ideas? Exhaust leak? Bad plug? Burnt valve?

[Lee H]

I would start with an ohms check on the wires, how old are they? Check to see if wire numbers 5 & 7 are touching anywhere. As they run next to each other in the firing order they could be cross firing, this usually happens under light load but could happen at idle. How old are the plugs, cap, rotor?

[68gmsee]

Could be several things, but start with exhaust leaks. That's the easiest thing to check. Look at all hoses carefully. I found a cracked one my BIL had missed by pulling it off and looking at the back side. If all that checks out then ignition parts can cause that including defective spark plug.

As LeeH mentioned check for crossfiring also. I like to do it at night by misting the dist cap and wires with a fine spray from water bottle.

[SoCalSlaughter]

Thats for the replys guys. The wires and dizy cap and rotor are new, maybe a month old, but the truck has been doing this long before. The spark plugs themselves I havent checked in awhile, I know they are under a year old though. And I havent heard or seen an exhaust leak, i installed new donuts on the manifolds maybe 2 months ago.

[storm9c1]

I agree with others. It's a 90, so TBI right? Could it be an injector misfiring?

[SoCalSlaughter]

The fuel injectors are new, Ive watched the srpay pattern with a light and the truck running and I dont see any drips. Also has a newer fuel pressure regulator.

[68gmsee]

Originally Posted by SoCalSlaughter

....The spark plugs themselves I havent checked in awhile, I know they are under a year old though. And I havent heard or seen an exhaust leak, i installed new donuts on the manifolds maybe 2 months ago.

Some time back I installed plugs in my truck and shortly afterwards it started a slight miss. I tracked it down to a new defective plug. These days you never know.

Have you also checked for intake leaks?

Unfortunately, there's several things that can cause the miss including distributor itself and/or emission parts. If you can have it diagnosed in a shop, that would be the easiest and fastest, otherwise, you just have to start eliminating.