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Nosolace001
July 15th, 2010, 06:48
OKAY, so about 2-3 months ago my check engine light came on shortly after using some lucas oil fuel injector cleaner. Now, I am not sure that that was the cause, but it happened in the same tank the additive was used.

I pulled the code and I came up with a Multiple Random Cylinder Misfire IIRC. First thing I did was replace the spark plug with the recommended champions, just because they were cheap and it couldnt hurt. The plugs were way over gapped, and when I replaced them, the engine ran better than ever, but still has the CEL. I also used an entire can of sea foam on it with no effect.

All of the threads I have read about cylinder misfires referenced hard starts, rough idling, and sometimes worsening fuel economy. I have not noticed any of these symptoms.

Is it possible that I have a bad sensor? Something that is falsely telling the computer I have a misfire? Please help! Emissions test coming soon, and AZ will fail just for the light :rolleyes:

kastein
July 15th, 2010, 08:24
What year XJ / engine etc hasta

Nosolace001
July 15th, 2010, 09:00
DOH! You might need to know that. 2001 4.0L, No engine Mods.

ParadiseXJ
July 15th, 2010, 10:03
Have you erased the code? My Jeep is a RENIX but my Altima and my Ranger are both 2002's and when they throw a code, the light stays, even if the problem is fixed. I can't speak directly to your problem but it could be that the code stayed and thus the light is still on.

I can't imagine that 4 oz of Lucas in 15 gals. of gas is going to cause it to make THAT much of a difference. The Sea Foam however could have gummied up the plugs/O2 (I've heard of that happening) and thrown the code.

Erase the code and see if the light comes back.

kastein
July 15th, 2010, 10:05
What cylinders was it? Cylinders 3 and 4 maybe?

Does the XJ run like crap occasionally when you restart it within a few minutes of turning it off?

X2 on what Paradise said, erase it, if it comes back, it is an actual problem. Note that some states won't pass you (mass is one of them) if you have cleared the codes in the last ~100 miles, so plan accordingly if your emissions checkup is coming real soon.

Nosolace001
July 15th, 2010, 10:18
I have cleared the code, both with a scanner and by unplugging the battery for 30+ minutes. Everytime I do, I drive about 10-15 miles before it comes back on.

It isn't just cylinders 3 and 4, that would point to the heat soak issue I have read about, but I have gotten 1, 5, 3, & 4.

The weirdest thing about this issue is that the jeep is running like a top. It has just over 80k on it, and since i replaced the spark plugs it feels like it is running like new! It has no symptoms what so ever that would tie it to anything I have read on here. That is the only reason I have continued driving it, I figured it was just a stupid sensor. But I am not about to start replacing every sensor and dumping a ton of money.

kastein
July 15th, 2010, 10:22
I have cleared the code, both with a scanner and by unplugging the battery for 30+ minutes. Everytime I do, I drive about 10-15 miles before it comes back on.

It isn't just cylinders 3 and 4, that would point to the heat soak issue I have read about, but I have gotten 1, 5, 3, & 4.

The weirdest thing about this issue is that the jeep is running like a top. It has just over 80k on it, and since i replaced the spark plugs it feels like it is running like new! It has no symptoms what so ever that would tie it to anything I have read on here. That is the only reason I have continued driving it, I figured it was just a stupid sensor. But I am not about to start replacing every sensor and dumping a ton of money.
yep, that heatsoak issue is what I was shooting for :cheers: Interesting problem, I'm really not sure what it could be. What's generally going on when the light comes on? Idling? just after a shift? random? running smoothly?

How's the idle? You say it runs like a top, but so did my 96 when I got it, and it had an ultra rough idle. New rotor, cap, plugs, and wires solved it. You don't have a cap and rotor and wires though... just a coil pack. hmmm.

Nosolace001
July 15th, 2010, 10:49
The last time I cleared the code it came on as I was traveling down the freeway, so no distinct events. The other time I don't recall, but nothing out of the norm when the light comes on.

The idle used to be sort of rough, but since I replaced the spark plugs it has been really smooth, a huge difference. In the time I have had it, it has had no overheating issues, no real rough starts (other than when I left it for a few weeks), and I had the Crankshaft Position Sensor go out.

Would a faulty MAF sensor cause the engine to believe it is misfiring? It believes it isnt getting the right amount of air? Maybe something on the exhaust side reading a lean exhaust incorrectly, indicating an incomplete burn?

I am leaning towards it being a sensor issue and not mechanical, based upon the way it is running. I guess it could be an intake gasket, or maybe even a head gasket? (I would think those gaskets would cause a larger problem, and noticeable symptoms)

Thanks for your help, I appreciate it.

joe_peters
July 15th, 2010, 14:09
No MAF, the 4.0 uses MAP and MAT.

Someone had a similar issue, his turned out to be cracks in the coil packs allowing random shorts to ground.

Note: Chryco recommended plugs for the distributor-less ignition are NGK V-Fires.

Nosolace001
July 15th, 2010, 14:32
I was suspecting the coil packs... good call. Depending on how much they are, I might just throw some new ones in. Maybe Pick up some V-Fires too

Thanks!

Nosolace001
July 16th, 2010, 12:00
Follow up for the forum's sake...

Replaced the ignition coils last night, there was a ticking sound prior to this that is now gone. I believe the ticking was the broken coil grounding out somewhere...

The check engine light is gone, and the jeep is running great

joe_peters
July 16th, 2010, 15:00
Glad you got it!