rough running 93 zj 4.0l atx

Aug 27, 2005 4 Replies
M

HELP me please.



story: bought a 1993 jeep grand cherokee with 173k on it. i have persisting problems. not sure if these are related?



symptoms: hard starting, excessive cranking rough idle, intermittent stall P to D or R rough running attempting to pass on highway



my mistakes:



173k replaced fuel pressure regulator and fuel pump (ouch) replaced spark plugs because some nut put bosch quadfires in it. immediately improved the hard starting problems.


183k replaced intake gasket for suspected vacuum leak. no improvement. replaced spark plug wires. no improvement. replaced IAC, no improvement. replaced crank position sensor connector, after which i promptly broke the sensor, and replaced that too. no improvement.



tested and found to be ok: tps, map, ect, iat, alternator, vacuum, coil.



ready to load the .45 i'm losing my mind here. not sure if i should shoot myself, or the truck.


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W

Did you also replace the cap and rotor when you changed the plugs and wires?

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M

the cap and rotor i did not replace because it was new just before i bought it. inside the cap is still clean with no deposits or carbon tracking.

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M

i remembered my kV probe and thought to myself, why not, but then i remembered i don't use it all that much, because all lexus now is DIS. anyways, i measured the kV on my cherokee. my results:

coil: 10.6

1-6: 9.6, 8.5, 10.3, 11.3, 12.5, 10.6

this morning i decided to go back to my original fix 10k mi ago. i replaced the spark plugs. now it starts good again. i remeasured the kV:

coil: 8.6

1-6: 6.5, 7.4, 9.1, 10.2, 9.2, 8.5

what would cause the plugs to foul out so fast? or is this normal? previously has champions in it. now i have ngk's.

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D

MudPuppy76 did pass the time by typing:

10k is too long to wait between spark plugs. I don't go any longer than 7,000 between replacements.

spark plug heat range, stop/start city driving where the engine doesn't get fully up to temp for long enough. CCV system plugged up and backfeeding oil into the air intake (look for an oily spot on the filter.

I run Autolite 3924, but that would be too cold for your application. Go one heat range up, 3925. Also check the plug wires, your still getting too much variance. It is acceptable to mix heat ranges, blocks don't cool evenly.

Runs about $100 but I like to have a local shop use a motorvac on my Jeep. (induction/rail cleaning)

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a lot better than dumping carb/fuel cleaner into the system. A plugged cat will also cause fouling.

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