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  1. #1
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    Default Misfire.... No power

    i have a 1988 XJ, it misfires when ive been driving for long distances. i drives great for shirt drives. at normal 210-220 temps after long drives it starts to misfire and the XJ has no power to accelerate. some times is dies out. just shuts off. i can start it back up but it starts and revs to about 2k then goes to 1k then off. if i wait 5min it starts fine but still misfires. ignition is all new CPS is new, Mustang injectors. just about every sensor on the jeep is new. i just had the Head bolts torqued and the timing chain replaced. it was misfiring before i had the work done. it actually ran better for a bit then started misfiring again.

    im also looking for a cheap Renix scan tool to try and diagnose this. any one know if Jeep dealers would have the scanners?

  2. #2
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    Icon1 Re: Misfire.... No power

    I have had similar issue's. What i found is one of the wire's inside my plug to the coolant temp. sensor was broken down inside the plug itself. I just stripped off a little insul. and pushed it down inside there real good, and pushed a wooden tooth-pic in behind it all the way and snipped it off at the plug. This made a realo big improvment. I hope this help's...
    PVT. Tadpol XJ

  3. #3
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    Default Re: Misfire.... No power

    Bypass your fuel pump resistor on the D/S front inner fender,.. small china looking thing, tie the two wires together , tape them up and go for a test drive

    Stock:
    2007 SRT8 Grand Cherokee w/2008 upgrades
    2004 TJ Rubicon
    2000 Cherokee Sport 2 Dr - Donor
    2000 Grand Cherokee Laredo
    1990 Comanche Eliminator
    1990 Comanche Sport Truck
    1989 Comanche Sport Truck
    1988 Comanche
    1986 Comanche Metric Ton Turbo Diesel
    1989 Cherokee Chopped Comp Rig

    and thats just the jeeps

    WWW.RACINGFORTHECURE.CA

  4. #4
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    Default Re: Misfire.... No power

    OK, something is worn out. So now to figure out what it is. The first thing to do is figure out if it is fuel or electrical related. What Jensen said is a good start. But I am thinking you have a sensor failure, particularly the O2 sensor. How long since that has been changed?
    230 hp 4.3L Chevy
    Built 4L60E with manual lockout
    Atlas 4 speed
    Griffin radiator
    On board air
    Warn 9.5ti on custom bumper
    7.5" RE front and bastard pack rear on custom long arms
    30 gal gas tank
    lockers
    And a bunch of other stuff

  5. #5
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    Default Re: Misfire.... No power

    I just replaced the 02 sensor. also for the fuel bypass, im a little confused. just tape the 2 wires together or am i cutting anything?

  6. #6
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    Default Re: Misfire.... No power

    I believe that is supposed to be a heated O2 sensor. You might want to check that. You need a good connection there. Any codes off the key switch thing?
    230 hp 4.3L Chevy
    Built 4L60E with manual lockout
    Atlas 4 speed
    Griffin radiator
    On board air
    Warn 9.5ti on custom bumper
    7.5" RE front and bastard pack rear on custom long arms
    30 gal gas tank
    lockers
    And a bunch of other stuff

  7. #7
    Join Date
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    Calgary, AB
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    Default Re: Misfire.... No power

    Quote Originally Posted by da9r00d View Post
    I just replaced the 02 sensor. also for the fuel bypass, im a little confused. just tape the 2 wires together or am i cutting anything?
    You can cut the wires if you want but I would suggest for diagnosis purposes , just use a scrap wire or spade connector to bypass that ballast resistor. Pretty common failure on old XJ's
    Stock:
    2007 SRT8 Grand Cherokee w/2008 upgrades
    2004 TJ Rubicon
    2000 Cherokee Sport 2 Dr - Donor
    2000 Grand Cherokee Laredo
    1990 Comanche Eliminator
    1990 Comanche Sport Truck
    1989 Comanche Sport Truck
    1988 Comanche
    1986 Comanche Metric Ton Turbo Diesel
    1989 Cherokee Chopped Comp Rig

    and thats just the jeeps

    WWW.RACINGFORTHECURE.CA

  8. #8
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    Default Re: Misfire.... No power

    Single wire = non-heated o2
    multi-wire = Heated o2

    but I believe the plugs are different so you cannot mix it up
    Stock:
    2007 SRT8 Grand Cherokee w/2008 upgrades
    2004 TJ Rubicon
    2000 Cherokee Sport 2 Dr - Donor
    2000 Grand Cherokee Laredo
    1990 Comanche Eliminator
    1990 Comanche Sport Truck
    1989 Comanche Sport Truck
    1988 Comanche
    1986 Comanche Metric Ton Turbo Diesel
    1989 Cherokee Chopped Comp Rig

    and thats just the jeeps

    WWW.RACINGFORTHECURE.CA

  9. #9
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    Default Re: Misfire.... No power

    the 02 sensor has 3 wires

  10. #10
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    Calgary, AB
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    Default Re: Misfire.... No power

    Did you try the fuel pump wires on the ballast resistor?
    Stock:
    2007 SRT8 Grand Cherokee w/2008 upgrades
    2004 TJ Rubicon
    2000 Cherokee Sport 2 Dr - Donor
    2000 Grand Cherokee Laredo
    1990 Comanche Eliminator
    1990 Comanche Sport Truck
    1989 Comanche Sport Truck
    1988 Comanche
    1986 Comanche Metric Ton Turbo Diesel
    1989 Cherokee Chopped Comp Rig

    and thats just the jeeps

    WWW.RACINGFORTHECURE.CA

  11. #11
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    Default Re: Misfire.... No power

    Jenssen I think your a Genius. I tried it and the XJ runs Great..... i drove it home from work as it misfired. i checked your post, wired it up and drove around for a while with no problems. im gonna drive for a while 2morrow and see what happens. i also put the wired back and it still ran great. ill keep you posted.

  12. #12
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    Default Re: Misfire.... No power

    Ok so what is happening is the ballast resistor has a hairline crack, when the engine temps in the bay come up the crack gets bigger. So in a perfect world your ballast resistor drops your voltage from 12V to say 8 volts ; when the hairline crack gets bigger due to the heat the voltage drops lower and lower which basically starves your fuel system,... your pressure will keep dropping and dropping. I would also want to bet when your misfire happens your engine temp creeps up pretty damn quick as its basically running really lean.

    The ballast resistor is only there because in the past XJ owners complained about noisy pumps,.. lower voltage keeps the pump quiet.
    Stock:
    2007 SRT8 Grand Cherokee w/2008 upgrades
    2004 TJ Rubicon
    2000 Cherokee Sport 2 Dr - Donor
    2000 Grand Cherokee Laredo
    1990 Comanche Eliminator
    1990 Comanche Sport Truck
    1989 Comanche Sport Truck
    1988 Comanche
    1986 Comanche Metric Ton Turbo Diesel
    1989 Cherokee Chopped Comp Rig

    and thats just the jeeps

    WWW.RACINGFORTHECURE.CA

  13. #13
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    Location
    Logan UT
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    Default Re: Misfire.... No power

    what is the "science" behind this ? anybody knows ?
    I mean the ballast resistor has to be here for a reason.... by passing it sure has consequences.... do you know what they are ? just curious as I have read this "fix" in different occasions...

    For the O2 sensor, if you have an 88 you may want to check service recalls on that.... my 89 was recalled to change the O2 sensor that had some problems.... I am going to go see a dealership with the recall papers so they check if it is still the original one.... and if it is then BAAAM free O2 sensor
    "if yer not larnin sumptin new everday, check yer pulse."

  14. #14
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    Default Re: Misfire.... No power

    Quote Originally Posted by steph74 View Post
    what is the "science" behind this ? anybody knows ?
    I mean the ballast resistor has to be here for a reason.... by passing it sure has consequences.... do you know what they are ? just curious as I have read this "fix" in different occasions...
    It's to quiet the Fuel pump,.. from owner complaints. My big jeep has been completely bi-passed for years now.

    87 and earlier Renix 4.0 XJ's didn't have them at all, sometime in '88 they started voluntarily recalling them and put them in for "excessive fuel pump noise"

    If I had more time today I would dig it up for you
    Stock:
    2007 SRT8 Grand Cherokee w/2008 upgrades
    2004 TJ Rubicon
    2000 Cherokee Sport 2 Dr - Donor
    2000 Grand Cherokee Laredo
    1990 Comanche Eliminator
    1990 Comanche Sport Truck
    1989 Comanche Sport Truck
    1988 Comanche
    1986 Comanche Metric Ton Turbo Diesel
    1989 Cherokee Chopped Comp Rig

    and thats just the jeeps

    WWW.RACINGFORTHECURE.CA

  15. #15
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    Location
    Logan UT
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    Default Re: Misfire.... No power

    I was just curious, and looking for someone to do my homework lol I'll look it up too.
    So this should not interfere with gas mileage or stuff like that ?
    I have a bit of a rough cold idling and also missfire and backfire especially when I let go the gas pedal.... maybe I should try that and see if it helps a bit....
    "if yer not larnin sumptin new everday, check yer pulse."

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