Throttle Junkie

97 4.0L SE
Typical rough idle, poor/choppy acceleration that one would expect with a miss. For what it's worth this coincided with an Alternator replacement. Charging system working fine after replacement.

CEL shows it's cylinders 3 & 4. It's not ignition related. I've replaced plugs and wires cleaned the Distributor cap and replaced roter. It has a single coil that controls the fire for all 6 cylinders.
I don't believe it to be fuel related. I replaced the injectors for both holes. It could be pulse timing, but this seems unlikely, and I have no way checking this. I would think the computer would be able to tell me if it where something like this with the injectors. I've done a hot soak thinking maybe it was deposit build up this did nothing. I'm at a loss now, The next logical thing I can think of is a valve issue of some sort. Possibly collapsed lifters? I haven't pulled the valve cover to see what they are doing when running.

I don't hear any intake leaks, and misting carb cleaner around the intake and vacuum lines does not change idle speed.



Any ideas what to do next?

fb97xj1

You should replace the cap when replacing the plugs, wires, and rotor. Cleaning the cap may not be enough. Check it for any visible cracks as the spark could jump from one terminal to another. I would replace it regardless as you already replaced the rest of it. Caps are cheap.

I dont recommend driving it with a misfire either as that is very bad for the engine. Any engine for that matter.

BlueRidgeMark

Hmmm. Did you pull plug wires for the alt replacement? Might have gotten them swapped.

I agree with fb, if you didn't replace the cap, that's a must.


Otherwise, valves are a possibility, as you mentioned.

Throttle Junkie

I replaced the cap to be on the safe side. Didn't change anything. I pulled my service manual and made sure all the wires were connected in the proper order. No one has any other ideas what could be wrong?

BlueRidgeMark

Compression test?