I've been lurking around here for years, but this is my first post. Grab some popcorn it's going to be a long one...
I have a misfire that's driving me crazy. I've thrown a lot of money at my ZJ trying to fix it with no luck...
It's a 1997 ZJ with around 200,000 miles, 4L and an auto tranny (42RE I believe). Sitting on 4 inches of Rough Country lift with 31x10.50 A/Ts and stock gears. The transfer case was acting up so, long story short, it's now a 2x4 ZJ.
It's been my daily driver for a year. No problems at all, it has run great.
About a month ago it started missing intermittently. No problems starting or anything like that. It fired right up and would drive fine. Out of nowhere, (normally, but not always, at a stoplight) it would start to run very rough (sounds like a small block v8 with a big cam), lose power and have a very bad exhaust smell.
I'm assuming what ever the problem is is screwing with the spark.
I drove it like that for a month, but now the problem is getting worse to the point of being unsafe to drive.
It always starts right up, but instantly starts missing and spitting unburnt gas out the tail pipe. It will drive around okay but has a huge loss of power and stalls randomly. The miss is throughout the whole RPM band. After it stalls it's hard to re-start. I normally have to crank it for awhile to re-start it when it does die. It will randomly run fine for about 30 seconds, then act up again.
No CEL or any codes...
Here is a list of what I've done so far:
-Checked all electrical connections and vacuum hoses.
Bench checked the following sensors:
All checked good.
I also removed and deep cleaned the throttle body, and know for a fact that it's not a clogged cat.
I don't have a gauge to check the fuel rail pressure but I'm assuming it's fine considering I have raw fuel coming out the tail pipe, and the miss happens throughout the RPM band as-well as at idle. I think that MOSTLY rules out a fuel problem.
I'm thinking upstream o2 sensor or the PCM...
Thanks in advance for any help!