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Discussion Starter #1
i have a 1988 Jeep 4.0L, it misfires. It has a new coil (MSD blaster), MSD 6a Box, distributor cap and rotor and wires. still misfires, it was misfiring a while ago so i changed the CPS and CKS and it ran fine. but now im back to the same thing. is there any test i can do to find the problem
 

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OK, so i changed my Plugs... Even thoe they are new (2months old) from Bosch to Champion. big difference, runs way better idles better. But.... when i press the gas raising the RPMs slow it runs fine, but when i Smash the gas it starts to misfire. what could it be? coil? Wires? im gonna try and put the stock coil back on since it was new
 

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hey did you find out anything because my engine light is coming on and i got it check and its a misfiring thing and i can figure it out and im kinda bogin a little like the truck isnt getting gas or would a misfire do that
 

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Double check your wires..sometimes they look like they are good but upon further inspection they are not actually staying plugged onto the spark plug. This happened to my 89. Just thought i'd throw it out there.
 

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Same problem with my '88 XJ, it started after installing Auto zone wires. The boot to the distributer cap wants to pop up on two of the wires so I get a slight miss off idle. Upgrade wires! :thumbsup:
 

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Discussion Starter #6
im getting a misfire when i have the gas pressed only a little bit, does not matter what RPM, but if i hold the gas down it revs fine. i have everything new on the ignition and new injectors. new CKS and CPS sensors. gonna try and change the 02 sensor. and the intake/exhaust gasket.
 

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Discussion Starter #8
Timing is good, haven't checked the Knock, checked the TPS, Clean and good. i might have a bad intake/exhaust gasket, and a bad 02 sensor but i don't think that would cause these symptoms. but i could be wrong
 

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I do not know about a 88 but I do know on other XJ's that the 02 sensors can cause backfiring, hesitation and other symptoms too. A bad intake/exhaust gasket should be audibly noticeable if there was a problem or you would notice soot........have you checked for a cracked exhaust manifold by the collector?
 

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You might also try checking your fuel pressure for consistent readings.

A friend of mine's xj was starving for gas and it "popped" when he pressed the skinny pedal. We replaced the fuel pump O-Ring, and it runs great.

Just a thought... ;)


I could very well be a blown intake/exhaust gasket as well.
:dunno:
 

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Still need help...... New knock sensor and new coolant sensor, NO CHANGE still misfires.

I think im gonna drive it off a cliff... but it would prob still be drivable after that.

im gonna take it into a shop and let them deal with it, ive already spend $1000 in sensors and ignition parts with no change
 

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Well, okay... if you're getting consistent fuel pressure on the rail, it could very well be electrical.

I remember having electrical problems with my old hotrod years ago. My SBC with the Mallory Uni-Lite would begin crapping out at at about 5,000RPM or so. I finally got it to rev after I installed an Accel HEI distributor and Supercoil. Never did figure it out!

I really don't what else to suggest, but to maybe hit the J/Y and grab up a stock ignition, pop it in and see if your problem goes away. And if it does, then you'll know where exactly the problem is...

Wish I had more to give!
:brickwall:
 

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I've seen where the dist. pick up coil would lose its connection from a broken wire. It'd make contact when idling, then when the dist. would advance it would lose it's connection. soon as you let off, it would reconnect. Seems you've replaced everything but the distributer. Throw another one in.
Deadeye
 

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Sounds familiar with mine. If you eased on the gas it was fine but as soon as you hard accelerated it would spit and sputter correct? If so what all did you have to replace?
 
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