misfire 1 and 3

again helping a friend out.

he said he ran a cel and it said that 1 and 3 are misfiring.

its stumbling at idle at 750 idle.

2001 cherokee auto 4.0

he changed the spark plugs and thats about it.

any hints?

What kind of plugs?

If Bosch, get em out of there........................NGK are the best choice for 00-01.

birchlakeXJ said:

What kind of plugs?

If Bosch, get em out of there........................NGK are the best choice for 00-01.

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Seconded. NGK V-Power for distributorless XJs.

Did this misfire occur after the XJ had been parked for 15-20 minutes? I.E., he parked it warm, shut down & walked away for a bit, then came back, started it up, experienced a rough idle and subsequently got the CEL for the injector misfires? If so, there's a known heat soak issue involving injector #3 on 2000 & 2001 XJs, though it is possible for more than one injector to throw a code when it happens (ask me how I know).

it happened before and after he changed plugs.

i think he always has the stumble so not sure if its heat soaked

Make sure of the plugs he installed. The distributorless 4.0s are fussy about the plugs. Don't use clown plugs in any XJ.

Quick and dirty test for heat soak--drive it and get it fully warmed up--at least 20 minutes. Park, shut off the engine, open the hood and let it sit like that for 30 minutes. Start it up--if the issue is gone or greatly reduced you have heat soak.

I just pulled out some fouled NGK's from my 2001 (extremely dirty, electrodes were pretty corroded).... I think they were NGK 6's (don't remember the full model number).

Are they really more highly recommended than properly-gapped Champion copper core plugs for our coil-railed XJ's? Don't mean to hijack, just curious.

anthrax323 said:

Are they really more highly recommended than properly-gapped Champion copper core plugs for our coil-railed XJ's? Don't mean to hijack, just curious.

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Yes. The OEM recommendation switched from (IIRC) Champions to NGKs a few years ago.

FWIW, the most troublesome plugs I've ever used across a range of vehicles have been Champions; about the only place I've ever seen them work even reasonably well is in air-cooled VWs. Their truck plugs were one of the worst things I ever installed in my XJ.

Back on track: just in case heat soak is the issue here, the only reliable method I've found to deal with it is as follows:

- Start the XJ. Check the temperature gauge once the engine is running.
- If there is no stumbling, drive normally.
- If there is stumbling, chances are the temperature gauge will be reading above 210degF (but hopefully not in the oh-crap-it's-overheating zone). If this is the case, let the XJ idle - and I mean idle; don't touch the accelerator - until the gauge gets back down to or just under 210degF; by this stage, the stumble should have cleared itself and it's OK to drive again.

Trying to drive it while it's stumbling will almost certainly result in a code being thrown and the CEL coming on. Just let the heat soak work itself out and you should be OK, assuming no further problems exist.

Recommended by Chryco, for what its worth.

If you were to take your 00+ distributorless 4.0 powered Jeep vehicle into a dealership with driveability issues they would check the plugs and swap them out if not NGKs before doing anything else.