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Old October 26th, 2013, 07:58 PM   #1
dochereford
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93 YJ 2.5L backfire

Okay, so I'm thinking I have a broken valve or something because the timing is steady (with a light). It will run smooth for a spell, then start back firing pretty bad, stalling, then it will smooth out again.

Any heads up suggestions before I tear into it?
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Old October 26th, 2013, 08:49 PM   #2
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Vacuum gauge..... If it's steady it's an ignition problem if it's shaking all over the place it's a valve train problem.
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Old October 26th, 2013, 09:02 PM   #3
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sprayed ether all over intake . no change in idle. i hook a vac to it and check tho. thx
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Old November 6th, 2013, 11:46 PM   #4
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Wow. Okay. I need some direction from some seasoned troubleshooters.

Vacuum held steady during backfires so I figured I had a ignition issue. Replaced cap, rotor, wires, plugs. Everything except coil. (hmm)

I noticed some water blowing out of tail pipe. Didn't seem like the normal condensation you get. So with that and the backfire, I decided to just pull the head, do a value job and be done with it.

I get it all back together. Runs great in the garage. I let it run for about 30 minutes to check coolant levels and such. Awesome

I take it for a spin and after about 5 miles, it starts doing the same thing again. (Nice going einstein. You did all that for nothing.)

I need a clue. I'll take a couple if you have some.
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Old November 7th, 2013, 12:42 AM   #5
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Distributor shaft loose?
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Old November 7th, 2013, 08:50 AM   #6
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You mean, does it turn? No its tight.
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Old November 7th, 2013, 08:54 AM   #7
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Coil?
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Old November 7th, 2013, 09:21 AM   #8
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tps
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Old November 7th, 2013, 09:34 AM   #9
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sounds like it might be getting too much fuel
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Old November 7th, 2013, 10:10 AM   #10
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Well, I'm done guessing. Too expensive. I need a method to start troubleshooting and frankly, I don't know where to start.
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Old November 7th, 2013, 11:02 AM   #11
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Just a thought have you checked that the plug wires are on correct? Proper firing order. I had someone mess with mine once and it acted similar to yours.
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Old November 7th, 2013, 01:41 PM   #12
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Timing is bouncing a little. When it misses and backfires, timing moves even more.
ONLY HAPPENS when its at temperature. Cold, it runs great.

I'm going to replace the distributor. One at auto zone comes with a new module. I figured it will eliminate two things. Module and cam drive gear.

If that doesn't work, I don't know what to tackle next. (...new engine...jeez)
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Old November 7th, 2013, 01:43 PM   #13
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Maybe a worn timing chain but I wouldn't think so because it stays running

If it comes to it I have motor that just needs an oil pan.....
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Old November 7th, 2013, 02:23 PM   #14
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Quote:
Originally Posted by dochereford View Post
You mean, does it turn? No its tight.
The bushings go bad and cause misfire/ detonation. The shaft will actually be sloppy, pull cap if and see if rotor wiggles if it does replace distributor.
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Old November 7th, 2013, 02:34 PM   #15
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Coolant temp sensor? If it only does it warm and you think its getting to much fuel I would guess ect
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Old November 9th, 2013, 12:14 PM   #16
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Update Solution:

Bad wire on the Crankcase Position Sensor. It was cutting in and out.
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