QueBallin1989

Hello all!
I'm having an issue with my 99 XJ Sport. I have a very rough idle, a pretty evident misfire, and a CEL for Random Multiple Misfire (p0300), Misfire on Cylinder 3 (p0303), and Misfire on Cylinder 4 (p0304). I did the typical fixes, new plugs, wires, distributor cap, rotor button, and ignition coil, and cleared the code. She idled much better and I thought all was fine and dandy...not quite. She started misfiring again and threw the same 3 CEL's. I've ran a fuel pressure test and I'm getting around 50 PSI. I unplugged the fuel injectors on 3 and 4 (separately) and there was no change in the way she ran, so I thought it was the injectors. But, my buddy was looking at it and the injectors will still pulsate. My question is where do I go next? Should I replace the injectors or does this sound like something internal?

Also, there is an exhaust leak just behind the downstream O2 sensor, which could account for part of the rough idle, but I wouldn't think it would cause this bad of a rough idle.

Any advice or suggestions is mucho appreciated!
Thanks and happy Jeepin!

warthog

Do a compression test

timmysixgun

Had a bad cyl 1 misfire on my 97. Tried everything. Tune up, tps, cps, coil, iac valve etc. ended up replacing cylinder one intake and exhaust springs. Problem solved for me. Try a compression test.

cruiser54

This seems to be a common fix.

But, I don't think it always shows up in a compression test.

We fixed a few by doing the water to remove carbon trick.



Pretty easy.

Get a cup of water, preferably something like a 24 to 32 oz. cup.
With the air cleaner off, hold the engine RPM at 2000 RPM or higher and dribble the water from the cup, which you've pinched to look like a spout on top, into the carb or throttle body. Go slowly and the engine will bog a bit. Stop and let it recover. Repeat until the cup is empty.

timmysixgun

Ah yes. Now that I think about it I had a cyl 1&3 misfire. Did a seafoam treatment and the cyl 3 misfire went away. Could always try that first. It's cheap and probably needs to be done anyway.

cruiser54

Use water instead of seafoam.

warthog

Sorry but I have to ask. Water????? This goes against everything I have ever heard. I'm not saying this will not work. But is it common practice or as common as seafoam? It took me months to work up the courage to dump seafoam into mine.

investinwaffles

Also, check + clean engine grounds and harnesses if you have not already. Check the O2 sensor harnesses as well, that has caused weird crap for me before. It honestly sounds like wiring if it is doing it all the time, or possibly bad injectors.

Its kind of hard for me to know if an injector is for sure firing, I would possibly try to swap injectors around to see if the problem persists (or better yet, borrow some injectors that you are sure work). You can get a test light for the actual harness, not sure about the injector (other than a multi-meter resistance test).



Water injection is very common, I run it on my mustang to cool the intake charge down, which lets me run more boost, and it keeps the motor extremely clean inside (I do run a methanol/distilled water mix, but same concept).
I just don't know how you a few minutes of steam cleaning is going to clear up enough though. I wonder if it is possible to rig something up so it would "spray" while you drive (think a small nozzle just before the throttle body). You may need to do several runs otherwise (also, I would do them at full operating temperature)

Actually, have you cleaned the Throttle body and electronics (IAC and such)? I would do that right before doing a seafoam or water injection treatment so you dont knock more crud into the motor.


I have had good luck with Seafoam in my Dad's 93 ZJ that idled like crap, but distilled water should do the trick as well (I would probably run distilled water, since its only like $1 a gallon).

Application is the same though. Ran about 1/3rd of a can through after I drove it for 30 or 40 minutes to get it nice and hot, and let it sit for 10-15 minutes before taking it out for another 30 minute drive. Ended up making such a difference that I did 2 more applications over the course of a weekend. Be aware of the consequences though - could knock dirt/carbon loose which is bad, etc. I would try diagnosing it further before going down that route.

cruiser54

Yes. Water.

You need to face your fears and listen to those with true experience.

Seafoam is a gimmick.

The water makes the carbon detach from places it's not supposed to be, like under the valves.