That 94 I have been playing with developed a new quirk.

It acts like a couple plugs are fouled/ dead cylinders. At idle, it is smooth as silk and has no hesitation. At speed it jerks and doesn't want to downshift so it feels like I am hauling a heavy trailer.

I pulled all the plugs to see what story they could tell, and to my surprise they all looked like they had just come out of the box. I wish my teeth were as white as those insulators. The arm didn't look discolored from heat, they just were really clean.

Strangely, 4 of them are Bosch iridium plugs, and the other 4 are Motorcraft. I double checked the gap on them before re-installing.


What am I looking at here?

I expected to find one or two that were different and go from there.

This is my first 8 cy Jeep and I am kinda out of my depth.

 

You may have a clogged catalytic converter, or a fuel starvation problem.

 

Thanks. Will look into both and report back. The muffler needs replacing, so I will be down there with tools anyhow to "unclog" the cat.

 

How would one diagnose a malfunction cat?

 

There are only 2 ways I know, check for backpressure or remove it and see if it runs better. I would remove it.

My wife's '89 Dodge K-car almost died on the highway. She called me and I came and got it, drove it home barely running, no power. Almost home, there was a bang and a lot of noise under the hood so I stopped and checked it out. The EGR valve was gone! It blew right off the manifold. I knew right then what was wrong. Plugged cat. I replaced the EGR valve and took the cat off. Power came back! I checked compression and I hadn't blown the head gasket yet, thank God.

I put a shop rag over the end of the converter and tried blowing thru it with my mouth. NOTHING came out. I was surprised the engine ran at all. When I gutted the converter, the matrix had collapsed and blocked the outlet.

I'm not telling you you should do this, BUT, I took a 3/4" steel rod the the converter on my '79 GMC truck and broke up the matrix in small enough pieces to blow out the pipe. It sure helped that tired old 302. For trucks, that was before OBDI. It sounded pretty good with a Flowmaster on it!