2.5 Cylinder 4 Misfire (Okay Compression)

[paulwjax]

HI guys - Long-time lurker, first time poster.
I've been searching the threads here but can't find the answer and I'm at wits end. I've rebuilt motors before so I'm no stranger to wrenching, but I'm at a loss of what to wrench on so I'm asking for help before I spend anymore $.

My 2000 Wrangler SE with a 2.5L in it has a stumble. I've done some troubleshooting, and even fired the parts cannon a couple times, which has actually helped some, but the stumble remains. What I've done so far is listed below:

1. This started a month back and it was random, no CELs at the time, and didn't happen much, driving along I would give it a bit of gas and it would stumble a little around 1200 rpms and somewhere around 2500 rpms it would just "get it" and eveything would be normal again.
2. Flash forward to a week ago, the stumble happened every time I drove and it would bog down and die. I thought it was a bad fuel filter so I replaced the fuel pump and strainer. It wouldn't die anymore but it still stumbled.
3. I read that a dirty IAC and throttle body can cause stumbling. I cleaned them so you could eat off them and even replaced the IAC since it looked pretty sketchy, and reset the PCM. Still no luck.
4. I replaced the spark plugs, rotor, coil, and wires. Reset the PCM, no CEL, no change.
5. Replaced the upstream O2 sensor and the RPMs evened out and hold 800 at idle.
6. I then got frustrated and replaced the TPS sensor and the MAP sensor. Reset the PCM, no CEL, no change.
7. Now I get a P0304 - cylinder 4 misfire. (And it has burned a little coolant, but no milky oil) I tested for bad compression thinking I had a bad head gasket and did 3 Dry compression tests. FSM 2.5L specs are 120 -150psi.
   • Test 1 | Test 2 | Test 3
   • Cyl 1: 150 | 150 |150
   • Cyl 2:130 |130 |130
   • Cyl 3: 150 |150 |150
   • Cyl 4: 160 | 155 | 155

I was all ready to get bad compression numbers on Cyl 4 and replace the head gasket but those numbers look reasonable-ish and the low number was on Cyl 2 not Cyl 4.

Any thoughts what to test next?

 

[macleanflood]

Crank position sensor and the cam sensor in the distributor?

-Mac

 

[paulwjax]

So I talked to a friend who suggested that if Cyl 4 had a misfire to swap the injector and see if the misfire follows the injector.
And it did. I swapped it to Cyl 1 and got a Cyl 1 misfire. Getting new injectors now.