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Unread 04-07-2013, 02:54 PM   #1
TexasstyleZJ
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1994 ZJ 
 
Join Date: Apr 2013
Location: Sweeny, Texas
Posts: 6
Stalls, Backfires, Sometimes dies on idle

Hey ZJ owners, I know many of us have come across this same issue and I have read endless threads on recommendations for fixes and I have tried and tried to cure mine. ZJ picks its time to act up, sometimes it will run like a champ for about 30 minutes but then starts acting up, stalling and backfires, sputters. No check engine light, no codes with the three key turns except 1255, battery has been disconnected in the last 50 starts. This all started after trashing my trans in the mud and replacing it with a junkyard swap. Crankshaft sensor had to be replaced to get the jeep to start again after the install but has not run strong sense. Cap, rotor, plugs, wires, cam sensor, fuel pump, filter, new PCM, tps, cleaned throttle body, Seafoamed, fuel pressure is good, replaced O2 sensor, cut off the CAT. I have sprayed vacuum lines with carb cleaner looking for leaks, sprayed with soapy water looking for leaks. I have shaken wires and jiggled connections, tapped on the main fuse box, PCM, no changes when symptons are or are not present. I cannot locate anything that triggers the response. Has anyone cured their issues, found an area to look more into connections? PLEASE HELP MY POOR BEAST and my pocketbook....

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Unread 04-07-2013, 08:12 PM   #2
ZeeJay1997
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1997 ZJ 
 
Join Date: Dec 2008
Location: Sweet Home, Alabama
Posts: 6,448
What brand crank sensor did you use and how was it installed?
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Unread 04-08-2013, 08:24 AM   #3
TexasstyleZJ
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1994 ZJ 
 
Join Date: Apr 2013
Location: Sweeny, Texas
Posts: 6
Picked it up from Oreilly, my guess is your recommend the Mopar brand? Man, getting to that particular sensor s*cks to! I read your 12 step program Zee and thought I had it licked when I cleaned some connections but then about 10 miles out, the sputters and misfiring returned.
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Unread 05-08-2013, 07:44 AM   #4
TexasstyleZJ
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1994 ZJ 
 
Join Date: Apr 2013
Location: Sweeny, Texas
Posts: 6
So after trying a few more things I have found that my fuel pressure at the rail was 34 psi, I replaced the fuel pump and filter again with a direct OEM replacement with no change. I pulled and capped the vacuum off of the fuel pressure regulator and the pressure jumped to 44 psi. At this time I figured I had it worked out but after driving it and getting up to running temp, it starts misfiring and popping all over again. Does this give anyone any ideas?
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Unread 05-08-2013, 08:08 AM   #5
bigb229
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1998 ZJ 
 
Join Date: Feb 2010
Location: ga
Posts: 679
its that sh*t oreilly sensor....i put three in a row in mine and none of them would work. Picked one up from napa and it fired right up.
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Unread 05-08-2013, 08:12 AM   #6
TexasstyleZJ
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1994 ZJ 
 
Join Date: Apr 2013
Location: Sweeny, Texas
Posts: 6
Thanks big, I am going to look at getting a mopar replacement. Did you happen to check your fuel pressure when you were having the issue or do you know if the sensor would throw that reading off? I am just puzzled that my pressure is still down. But maybe the misread if just affecting it.
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Unread 05-08-2013, 08:27 AM   #7
KoreaZJ
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1994 ZJ 
 
Join Date: Aug 2011
Location: GANGNAM STYLE
Posts: 2,666
Quote:
Originally Posted by TexasstyleZJ View Post
I am just puzzled that my pressure is still down.
FSM says at idle... ~31 psi, ~39 psi with vacuum line removed.

You have 34 and 44. Difference should be 8-10, which you have.
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Unread 05-08-2013, 12:43 PM   #8
bigb229
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1998 ZJ 
 
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Location: ga
Posts: 679
my fuel pump checks out just fine. had the shop double check it today.
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Unread 05-08-2013, 01:07 PM   #9
Rich93ZJ
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1993 ZJ 
 
Join Date: Sep 2012
Location: Richland, Ga
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Im with (bigb229). Mopar only on the crank sensor.
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Unread 05-10-2013, 11:03 PM   #10
TexasstyleZJ
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1994 ZJ 
 
Join Date: Apr 2013
Location: Sweeny, Texas
Posts: 6
Thanks guys, I'm going to look into the CPS from mopar, it's gonna be a few weeks before I can get it but will post update.
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