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p0301 missfire help

J

jakecarder

NAXJA Forum User
Location
hagerstown md
My 00 Cherokee has a cylinder one missfire. I have started numerous threads in other forums but to get no answers. I have always read stuff on here and decided to give it a shot. First if anyone can point me in the direction of how to search on naxja that would be sweet.

Its a 2000. 4.0. Nothing special. What I have done to trace this problem is compression test, came out fine I have numbers if anyone's untreated, swap injectors from cylinder one and two, new coil, new spark plugs, clean all sensors in throttle body and clean throttle body. Oil has no antifreeze in it. I am losing a little bit tho. I need to take the plugs out and look at the top of the pistons to see if that's the probem

Heres the kicker. The engine will only run crappy when I am off throttle and moving. Like coming to a stop light or off the high way. When ever the engine is under load it runs great. If I am coming to a stop or slowing down I throw it into neutral and everything is fine. It seams to not like the 1100 rpms but does the 600.

Any input to this at all is helpful. Thanks and hope to join this,
 
spray around the manifold with carb cleaner and see it it has a vacuum leak causing that cylinder to run lean, also unplug the number 1 injector and look at the connector, are the pins "tight" where they would have a snug fit on the injector? It is a very overlooked common problem
 
I looked at the pins and yes they were fine. Would it hurt to put some di electric grease on them? The spraying on them would be while city's running and listen if it runs different?
 
Dielectric grease is an insulator. Adding it to any connection that does not otherwise make good electrical contact is at best useless. I don't know if it is common to add it to injector connections but it will not in and of itself solve your misfiring problem.
 
Last edited:
have you tried fuel filter.

i had same problems as you, my theory is this...

clogged filter = low fuel pressure at low load = crappy idle.

clogged filter at high load = fuel filter has internal bypass (correct me if i am wrong) which now lets engine have all fuel it needs..

i re-iterate, just a theory, but replace the filter $$$cheap$$$ thing to do anyway...
 
Does it do this from Cold, or it a Hot engine issue?

OBD II Engines have a heat soak issue and with the multiple cats on 00 though 01 units, the problem got much worse.
 
Ill try the fuel filter. What your saying sounds correct but I don't know. Its worth a shot before I go start replacing a head.

My Jeep also suffers from the heat soak issue. But that's a whole other issue.

Thanks guys
 
See this thread about the cam sensor in my 98 4.0. I had a pretty constant P0301 code and check engine light and slight miss for 2 years, after synching my cam sensor it is running like new, no audible misfire anymore. The check engine light and p0301 code has come on once (went off the same day) in the past 2 months since I synched it. Might be worth a shot.

http://naxja.org/forum/showthread.php?t=1086860&highlight=p0301
 
jakecarder said:
Ill try the fuel filter. What your saying sounds correct but I don't know. Its worth a shot before I go start replacing a head.

My Jeep also suffers from the heat soak issue. But that's a whole other issue.

Thanks guys[/QUOTE

Your fuel filter on a 2000 is part of the fuel pump in the tank, so good luck. I have a 2000 with a cyl 4 misfire that I have been chasing for months and I'm $500 in the hole and still have no clue what it is, so keep us posted of your findings.
Click to expand...
 
The fuel filter is part of the fuel pump.there are some Chrysler tsb,s for missfire issue's on the 4.0. The valves carbon up and won't seal properly.one of the cause they say is the valves don't rotate when the engine is running. The Chrysler fix is to remove the valve cover . Add compressed air to each cylinder 1 at a time .use an on car valve spring compressor .compress the spring and rotate the exhaust valve 1/4 of a turn .the run the engine with decarbon cleaner.this may or may not be what is your cause.
 
jeeptec said:
The fuel filter is part of the fuel pump.there are some Chrysler tsb,s for missfire issue's on the 4.0. The valves carbon up and won't seal properly.one of the cause they say is the valves don't rotate when the engine is running. The Chrysler fix is to remove the valve cover . Add compressed air to each cylinder 1 at a time .use an on car valve spring compressor .compress the spring and rotate the exhaust valve 1/4 of a turn .the run the engine with decarbon cleaner.this may or may not be what is your cause.
Click to expand...

not a bad idea to remove the carbon buildup, but I don't think he'd have gotten acceptable compression numbers if the valves weren't sealing well.

"off throttle" misfires are more often caused by a vacuum leak-- that's when the engine is pulling it's highest vacuum due to closed throttle plate and increased RPM.
 
Shorty said:
not a bad idea to remove the carbon buildup, but I don't think he'd have gotten acceptable compression numbers if the valves weren't sealing well.

"off throttle" misfires are more often caused by a vacuum leak-- that's when the engine is pulling it's highest vacuum due to closed throttle plate and increased RPM.
Click to expand...

My buddy had this exact issue. Narrowed it down to #1 cylinder. Decided to replace the valve springs. When injecting air into the cylinder he had a hiss. Pried up on the valve spring for the exhaust valve and hiss went away.

He used various injector cleaners, BG 44K etc and nothing helped.
It wasn't until he used the old mechanic's trick of carefully dribbling water into the throttle body with the engine at about 2,000 RPM that the problem was solved.
 
Just want to add that I have had a cyl 4 misfire for over 3 months and have dumped hundreds of dollars into it, mine to had good compression results but I decided to replace the valve spring and to my surprise it fixed it...... $16 and 1.5 hrs and it runs as good as new. Mite be something to try.
 
Dcoy1283 said:
Just want to add that I have had a cyl 4 misfire for over 3 months and have dumped hundreds of dollars into it, mine to had good compression results but I decided to replace the valve spring and to my surprise it fixed it...... $16 and 1.5 hrs and it runs as good as new. Mite be something to try.
Click to expand...

My buddy replaced his spring on the offending cylinder's exhaust valve and still had the problem. There must have been a bit of carbon between the valve and valve seat on his.
 
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