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Old 04-25-2011, 11:00 AM   #1
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Tried everything to stop the misfire...Help!

Okay, I'm working on my brother's 95 4 cylinder YJ and it has been acting like it is misfiring. As you push on the gas, it intermittently will miss. It is not every time I push on the gas though. It will be fine for 5 seconds and then do it ocassionally. Usually under a load it is worse.

We have lived with the problem until this past weekend it just started the miss almost all the time while you push the pedal down. When it is idling it misses occasionally but not constantly. We changed the coil last night and now it randomly does it again.

Here is what we have changed so far:
Spark plugs
Spark wires
Ignition coil
Distributor cap/rotor
Crankshaft position sensor
Throttle position sensor
Cam sensor or pickup
Oxygen sensor
Fuel filter



Any help would be appreciated!

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Old 04-25-2011, 11:23 AM   #2
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I'm by no means an expert, but have you checked your grounds? I had a 4Runner that was missing like crazy and it ended up being a grounding issue.

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Old 04-25-2011, 11:48 AM   #3
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Do you happen to know where the ground/grounds are located on the YJ's? But I will also add that to the list, thanks!
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Old 04-25-2011, 12:08 PM   #4
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I honestly wouldn't even know where to begin bro, sorry.
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Old 04-25-2011, 05:03 PM   #5
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Have you thought about the tming chain? Easy and cheap to do.
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Old 04-25-2011, 05:55 PM   #6
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Check all of the injector plugs to make sure they are tight and in good shape
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Old 04-25-2011, 09:46 PM   #7
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-We just cleaned out the grounds. No Change.
-We just unplugged all the injectors to make sure they are clean and also checked the electric on them and they seemed good.

Still nothing yet.
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Old 04-25-2011, 10:08 PM   #8
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Have you done a compression test?
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Old 04-26-2011, 10:54 AM   #9
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Quote:
Originally Posted by JonsBlue90 View Post
Have you done a compression test?
Yes we did and still nothing has changed. Now we can check that off the list too.
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Old 04-26-2011, 11:31 AM   #10
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had a problem like that once with a mustang and it was bad gas. put in a gas tank drying additive and put in new high test BP and it seemed to stop. What else is there that you haven't checked.........Driller
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Old 04-26-2011, 12:16 PM   #11
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Quote:
Originally Posted by Driller View Post
had a problem like that once with a mustang and it was bad gas. put in a gas tank drying additive and put in new high test BP and it seemed to stop. What else is there that you haven't checked.........Driller
What is the "high test BP"?

As for what we have not checked; I really can't tell you what is left...

Here is everything we have done as of now:
Spark plugs
Spark wires
Ignition coil
Distributor cap/rotor
Crankshaft position sensor
Throttle position sensor
Cam sensor or pickup
Oxygen sensor
Fuel filter
Grounds
Injectors cleaned and checked the ohms going through
Compression in cylinders
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Old 04-26-2011, 12:40 PM   #12
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Double check the voltage going to the coil, pull the plugs to try and determine which cylinder is misfiring or if you have a lean condition, pull the main connector off of the CPU and make sure all the terminals are clean and making good contact. Had an F150 misfiring under load and went through all of the same steps, turned out to be a bad contact at the CPU. Worth a shot, it's free.
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Old 04-26-2011, 12:50 PM   #13
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Have you checked it to see if any codes have popped up?
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Old 04-26-2011, 02:52 PM   #14
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Have you checked it to see if any codes have popped up?
No codes have come up. That is what we have been hoping for though. We checked the light on the check engine and it is working fine too.

@Therunner, thanks for the info we will try those steps next.
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Old 04-26-2011, 02:57 PM   #15
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Im not sure if there is a way to test or not but could be just a bad injector.
my dads f 150 had one go bad and when it was idling you could barley tell.
but when you accelerated it was really sluggish and would sputter and fall on its face. and since it sounds like youve tested for fire with no red flags im guessing its a fuel problem.
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Old 04-28-2011, 12:29 PM   #16
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i would like to know what the compression was of all the cylinders, also you are going to want to check you vacuum let me know what that is it should be steady at idle about 18-21, i don't think that a timing chain is going to be the problem if you are not hearing a lot of noise or a problem all the time. random misfire can be a carbon build up as well you might want to get some SeaFoam and run that as it tells you.

Nick
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Old 04-28-2011, 02:27 PM   #17
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Quote:
Originally Posted by Wantstojeep View Post
i would like to know what the compression was of all the cylinders, also you are going to want to check you vacuum let me know what that is it should be steady at idle about 18-21, i don't think that a timing chain is going to be the problem if you are not hearing a lot of noise or a problem all the time. random misfire can be a carbon build up as well you might want to get some SeaFoam and run that as it tells you.

Nick
The compression came in at a little over 115 psi per cylinder.
I'll look into the vacuum pressure and let you know.

Thanks for the help!
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Old 04-29-2011, 05:28 AM   #18
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i just had the same problem. i would b driving and the check engine light would come on and it would miss and then correct and only often then some days would do it bad. I replaced all that u did then come to find out it was a fuel injector connector on my last fuel injector. check those, they cause what u are talkin about. specially if you have got a few miles on it

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