If you were an XJ

And you decided that you wanted to throw a code for "Random Misfire," what would you do?

Little backstory: I was waiting in the drive-through at Steak and Shake for literally 30 minutes like the lazy american i am, before i decided to just shut the truck off because i wasn't going anywhere. Sat for 10 minutes, then the line moved. I started the Jeep, and it sounded and felt like it was running on 3 cylinders at best. It wouldn't move, and i had to sit there for about a minute before it smoothed out again.

About 5 minutes after it smoothed out, it threw a check engine light.

After another 20 minutes of waiting to get my food (while still running, didn't want to shut it off again.), i went to the gas station real quick, checked under the hood, (Yep, engine was still there) and continued on my way. It ran and drove perfectly, but that yellow CEL was just mocking me.

Ate my delicious (but not worth the wait) Peppercorn Melt and Chili Mac Supreme, drank my large (light ice) sweet tea, and drove the XJ down to my local Vatozone. (Making sure to romp on the loud pedal a time or two) It ran and drove perfectly.

Vatozone ran the code, and came up with "Random Misfire."

Suggested that i replace the coils and ignition control unit. Seemed reasonable, since i don't really know when the last time this thing had a tune up was. I'm looking at $140 for plugs, coils (apparently the control module is built in on this thing), and the little wire/boot things that go with the COPs? (Don't remember what they're called, COP is somewhat foreign to me.)

Seeing as it's running perfectly now, is it plausible to attribute the problem to underhood heat build up from idling in place for 30 minutes straight? If so, how do i clear the code?

What's the ignition replacement interval on these things?

crank or cam position sensors? At least the cam position sensor tends to go intermittent before full failure.

Put an LSx in it.

Has it done this idling for 30 min like that before? If not, I'd chalk it up to a bit of carbon build up from running a bit rich while idling.

Try to replicate it in your driveway and see what happens. Then pull the plugs and inspect. If they look OK, then it's time for replacements OTOH, if things are really ratty underhood, then it's time for replacements, too..

Crank position sensor, When they get warm (idling for 30 minutes will do that to them) they start acting funny. then they go out all together.

that is where I would start.

Try plugs first then replace the COP (with boots) I have seen a few COP fail but for the most part the plugs seem to cause most P0300 on that engine .

And go from there.

Paul B

You are really asking "how do i clear the code?"...ok...

Scan tools can reset CELs, or multiple non-error trips will allow the computer to shut it off on its own. See if "Vatozone" will reset it for you, but typically when you ask they say no, but I've found if you don't ask they will reset it for you. Try saying something like "man do I really have to buy a scan tool just to reset a silly CEL", they might feel bad for you and just do it. YMMV

As far as the cause, I'm guessing this is a 2000-2001 XJ? There is a known problem with the coil packs overheating and having misfires. I thought there was a recall for this but I could be wrong. The fix I know included insulation of the coil packs and wire boots.

EricM wrote: Crank position sensor, When they get warm (idling for 30 minutes will do that to them) they start acting funny. then they go out all together. that is where I would start.

Easy and cheap to replace if it's the CPS?

miatame wrote: You are really asking "how do i clear the code?"...ok... Scan tools can reset CELs, or multiple non-error trips will allow the computer to shut it off on its own. See if "Vatozone" will reset it for you, but typically when you ask they say no, but I've found if you don't ask they will reset it for you. Try saying something like "man do I really have to buy a scan tool just to reset a silly CEL", they might feel bad for you and just do it. YMMV As far as the cause, I'm guessing this is a 2000-2001 XJ? There is a known problem with the coil packs overheating and having misfires. I thought there was a recall for this but I could be wrong. The fix I know included insulation of the coil packs and wire boots.

Yep, it's a 2000.

Is this something that i should be worrying about? Or just see if it continues to run fine and forget about it?

triumph5 wrote: Has it done this idling for 30 min like that before? If not, I'd chalk it up to a bit of carbon build up from running a bit rich while idling. Try to replicate it in your driveway and see what happens. Then pull the plugs and inspect. If they look OK, then it's time for replacements OTOH, if things are really ratty underhood, then it's time for replacements, too..

I don't think it's ever idled this long before. I think the longest it's idled previously was maybe 15 minutes trying to warm it up in the cold.

Under the hood looks great, it's been REALLY well cared for. I may just go ahead and replace the plugs anyways. This is the first vehicle i've purchased that i haven't really done a full tune-up on first thing...

92CelicaHalfTrac wrote:

EricM wrote: Crank position sensor, When they get warm (idling for 30 minutes will do that to them) they start acting funny. then they go out all together. that is where I would start.

Easy and cheap to replace if it's the CPS?

It is about $35 if I remember correctly. It is on the back of the bell housing, not super easy to get to, but you don't need to remove anything to get to it.

EricM wrote:

92CelicaHalfTrac wrote:

EricM wrote: Crank position sensor, When they get warm (idling for 30 minutes will do that to them) they start acting funny. then they go out all together. that is where I would start.

Easy and cheap to replace if it's the CPS?

It is about $35 if I remember correctly. It is on the back of the bell housing, not super easy to get to, but you don't need to remove anything to get to it.

Eh, as long as i don't have to disassemble half the motor, doesn't bother me. Can't be worse than the starter on a DOHC Saturn.

Thanks!

I'll probably just go ahead and order one and throw it and some new plugs at it and see what happens.

It is a Chrysler product. If it has more then 30k on the plugs, replace them. Clear the codes out and drive it until the light comes on again. For some reason, probably trying to make the old technology work awhile longer with new controls, the architecture seems to promote excessive fueling with retarded timing, pinging machine!, to make everything work. So, it really is easy to flood the old stuff with EFI out if the plugs have some miles on them, especially when just idling for long times. I can feel this happen with my Dakota all the time. It loads up and the idle changes pitch. Time for a neutral throttle crack to "clean it out".

I vote plug wires. Another thing, High mileage, the valve seals leak, the high vacuum at idle draws the oil in and fouls the plugs. Had a 6 cyl Gremlin that did that.

iceracer wrote: I vote plug wires. Another thing, High mileage, the valve seals leak, the high vacuum at idle draws the oil in and fouls the plugs. Had a 6 cyl Gremlin that did that.

That's possible... but it hasn't lost a drop of oil in the last 2500 miles, so it can't be that bad, right?

Does this thing have plug wires? I'm not sure how COP is laid out, and i haven't taken a close look.

COP's are one long piece that bolts to the head with 4-13mm headed bolts through the pack. There are boots, no "wires", that connect the pack to the plugs.

If an ABS light comes on in a 4.0L Jeep I replace the crank sensor. If there is a tire low twice in a month I replace the crank sensor. If my wife's minivan is low on washer fluid I replace the crank sensor on the nearest 4.0L Jeep.
I think it might be the crank position sensor, unless it was done in the line at Steak and Shake.
And if you replace the plugs, USE the correct Champion plugs. I can't tell you how many times as a tech at a Jeep dealer I had a rough running Jeep, or a MIL for misfire and the customer said the plugs wer new. 90% of the time, if they weren't Champions, I'd spin in 6 champions and the problem would be gone.

DrBoost wrote: And if you replace the plugs, USE the correct Champion plugs.

True.

The 4.0L hates being spoiled. Give her 87 octane, the cheapest 10w-30 you can find, and the cheap plain Jane Champion plugs and she will love you.

I have a 02 WJ with the 4.0.

I suspect this will work on your XJ:

Put the key in the ignition, and turn to run (not start), then off, then run, then off then run again, and you should see codes on your odometer. You should wait on the run position just long enough for the odo display to come up. Each code will flash briefly, then your odometer will show "dOnE".

Not really a troubleshooting tip, so much as a possible way to skip a trip back to the car parts place just to pull codes.

meh...I've had good luck with cheap Autolites. 145k and never had to turn a wrench except for a leaky water pump and...of course plugs and wires

As others have said CPS is a huge issue with them. But other than that what year XJ do you have? Late model (1999-2003) 0331 cylinder heads are notorious for cracking letting coolant in and misifires galore.

I'm lucky i have a 98 TJ

a401cj wrote: meh...I've had good luck with cheap Autolites. 145k and never had to turn a wrench except for a leaky water pump and...of course plugs and wires

Is that the 401 in your screen name? If so then that's fine. The I-6 really, really likes Champion (RL12YC if I'm not mistaken). The 4.0L in particular is finicky.

eebasist wrote: As others have said CPS is a huge issue with them. But other than that what year XJ do you have? Late model (1999-2003) 0331 cylinder heads are notorious for cracking letting coolant in and misifires galore. I'm lucky i have a 98 TJ

It's a 2000, and other than this one incident, it's run 110% perfectly. Even every day past the incident.

It doesn't use nor leak any fluid at all. I know the 00-01 heads on the XJs are more prone to failure, and i went into the purchase knowing that. Luckily i only paid $3000 for it, and it's in pretty incredible shape. I won't be mad at all if it pukes a head down the road, but if it hasn't yet, i doubt it will anytime soon.