Random misfire: cylinders 3 and 6
03-01-2011, 05:33 PM
#1
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Year: 2001
Model: Cherokee
Engine: 4.0
Random misfire: cylinders 3 and 6
I recently changed the plugs in my 2001 due to a very slightly rough idle. After changing the plugs, Ive developed a miss. The engine light didnt come on for a few days, but I knew right away I had one. Engine light came on today, I had Auto ZOne check the code.
Random misfire, cylinder 3 and cylinder 6.
I cant figure what would be causing it. New Champion copper plugs, fairly new coil pack, etc. Here's the thing, it only misses at idle. Once I get on the gas, it revs smooth and powerful.
I can only think of 3 things, none of which seem to me that they should be wrong but any advice is welcome: vacuum leak (cant find one if its there), o2 sensor (shouldnt this throw a code?) or clogged injectors.
Ive got some lucas injector cleaner ready to drop in there, but didnt want to touch it till I checked here. Any help would be greatly appreciated.
Random misfire, cylinder 3 and cylinder 6.
I cant figure what would be causing it. New Champion copper plugs, fairly new coil pack, etc. Here's the thing, it only misses at idle. Once I get on the gas, it revs smooth and powerful.
I can only think of 3 things, none of which seem to me that they should be wrong but any advice is welcome: vacuum leak (cant find one if its there), o2 sensor (shouldnt this throw a code?) or clogged injectors.
Ive got some lucas injector cleaner ready to drop in there, but didnt want to touch it till I checked here. Any help would be greatly appreciated.
03-01-2011, 05:37 PM
#2
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Year: 1999
Model: Cherokee
Engine: 4.0
Put the injector cleaner in. No harm with that no matter what. Lucas is a good product.
Verify fuel pressure. Must be done with a gauge. With an 01, you are looking for 49 psi, plus or minus 5 psi. Fuel delivery is something that any technician would rule in or out very early in the troubleshooting process, as it can cause random misfires. Most big box parts stores will rent you a gauge for a few bucks.
Keep a very close eye on the coolant level in the coolant reservoir. You have a 2001, which has the "infamous" 0331 cylinder head, which has a known casting defect between cylinders 3-4. A crack there can lead to mysterious misfires.
Not saying that is what your problem is, but I am recommending that you watch your coolant level like a hawk ALWAYS.
And the #1 symptom of a cracked 0331 cylinder head is unexplained coolant loss.
Verify fuel pressure. Must be done with a gauge. With an 01, you are looking for 49 psi, plus or minus 5 psi. Fuel delivery is something that any technician would rule in or out very early in the troubleshooting process, as it can cause random misfires. Most big box parts stores will rent you a gauge for a few bucks.
Keep a very close eye on the coolant level in the coolant reservoir. You have a 2001, which has the "infamous" 0331 cylinder head, which has a known casting defect between cylinders 3-4. A crack there can lead to mysterious misfires.
Not saying that is what your problem is, but I am recommending that you watch your coolant level like a hawk ALWAYS.
And the #1 symptom of a cracked 0331 cylinder head is unexplained coolant loss.
Last edited by tjwalker; 03-01-2011 at 05:41 PM.
03-01-2011, 06:00 PM
#4
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Year: 2001
Model: Cherokee
Engine: 4.0
Put the injector cleaner in. No harm with that no matter what. Lucas is a good product.
Verify fuel pressure. Must be done with a gauge. With an 01, you are looking for 49 psi, plus or minus 5 psi. Fuel delivery is something that any technician would rule in or out very early in the troubleshooting process, as it can cause random misfires. Most big box parts stores will rent you a gauge for a few bucks.
Keep a very close eye on the coolant level in the coolant reservoir. You have a 2001, which has the "infamous" 0331 cylinder head, which has a known casting defect between cylinders 3-4. A crack there can lead to mysterious misfires.
Not saying that is what your problem is, but I am recommending that you watch your coolant level like a hawk ALWAYS.
And the #1 symptom of a cracked 0331 cylinder head is unexplained coolant loss.
Verify fuel pressure. Must be done with a gauge. With an 01, you are looking for 49 psi, plus or minus 5 psi. Fuel delivery is something that any technician would rule in or out very early in the troubleshooting process, as it can cause random misfires. Most big box parts stores will rent you a gauge for a few bucks.
Keep a very close eye on the coolant level in the coolant reservoir. You have a 2001, which has the "infamous" 0331 cylinder head, which has a known casting defect between cylinders 3-4. A crack there can lead to mysterious misfires.
Not saying that is what your problem is, but I am recommending that you watch your coolant level like a hawk ALWAYS.
And the #1 symptom of a cracked 0331 cylinder head is unexplained coolant loss.
I just put a new head gasket and re-manned head on it back in November. No coolant loss, Im very watchful of it since then.
I'll check the fuel pressure this weekend. Thanks for the input.
03-01-2011, 06:01 PM
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Year: 2001
Model: Cherokee
Engine: 4.0
I wasnt happy to pay it but it needed done.
03-01-2011, 06:09 PM
#6
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Year: 2000 sport
Model: Cherokee
Engine: 4.0
my problem was after i replaced coil pack and cam sensor....BAD plugs-champion which is recommended. after trouble shooting for a week, i bought a new set of plugs and started up fine and now running perfect. All this after r and r plugs, no issues just maintenance .
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