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  1. Fouling out spark plugs

    I have a 88 YJ 2.5 L 4 cyl it seems to be over fueling and fouling out my plugs. Hooked it up to diagnostics and showed no codes or errors. I was told possibly thermostat, would that do it? Please any info at all would be greatly appreciated. Just had a new tune up a week ago and new plugs have already fouled out again. Thanks!

  2. #2

    Re: Fouling out spark plugs

    what kind of plugs are you running? bosch plugs are CRAP!! esp the platinum 4s and any plug like them!! is your air filter clean? and idk about the thermostat doing it, but anything is possible. and OBD1 isnt very good when it comes to trying to find codes, if it were OBD2 then you could hook it up to a good scanner and use MODE 6 and possibly find out exactly what it is thats wrong

  3. #3
    I have a good clean air filter. My plugs are just auto lite plugs. Never seen nothing like it. Tomorrow I am going to go ahead and change thermostats I figure it won't hurt.

  4. #4

    Re: Fouling out spark plugs

    may wanna look at the fuel pressure regulator too if TBI and clean the TBI good with carb cleaner idk, thats one i havent seen before

  5. #5
    The guy I took it to last week said my air filter was clean and I went and checked it just now and it's pretty dirty. You think that would do it?

  6. #6

    Re: Fouling out spark plugs

    yeah, id change it out asap!! if the filter isnt allowing enough air through then you will have a fuel rich mixture going into your cylinders and that could be causing the plugs to foul, you also should check your timing and coil. if the timing is to advanced or retarded then it wont ignite the mixture correctly, and if the coil is weak then it wont produce enough spark to burn it corre3ctly, also check the gap in your plugs, just because they are new does not mean they were gapped correctly! ALWAYS ALWAYS ALWAYS check the gap in EVERY spark plug you buy before installing them!!

  7. #7
    Thanks so much! I'm getting a air filter now.

  8. #8

    Re: Fouling out spark plugs

    np, let us know what happens, and you wil want to pul the plugs, clean then good, check the gap and everything before you install the new filter and start it up! you can also get a spark tester and any parts store to check the spar from the coil to dist, and dist to plug

  9. #9
    Tomorrow I will put new plugs in and check for right gap and install new filter and I will let you know if that was my problem...I sure hope it is!

  10. #10

    Re: Fouling out spark plugs

    you;d be suprised at how much can go wrong due to the LITTLE thihgs!!!

  11. #11
    Ok I changed air filter and put in new plugs and still have the same problem. Any mor ideas? Thanks. Btw plenty of spark from coil and dist. Would dry rotted vac lines cause this problem?
    Last edited by tbfreeman; 05-23-2011 at 11:42 AM.

  12. #12

    Re: Fouling out spark plugs

    How sure are you it is Over Fueling, fouled plugs can be cause by too much fuel and not enough air, but a number of things, bad intake valve and or seats, mis-timed motor/ bad timing chain, bad rings to mention a couple.

    Bad vacuum would yield a very noticable drivability issue, not sure on the correlation to fouled plug(s)
    It used to be a jeep Thing,
    But all that stuff broke

    -Johnny-


  13. #13
    When I take off and change gears it is real sluggish . Took it to a mechanic he said over fueling and fouling my plugs out, he said gas is just pouring out of injector. Be about 2 weeks before he can look at it I really can't afford to wait that long. He wasn't for sure what was causing it. Hoping i could fix it before then. All mechanics in this small town is booked up. Thanks.

  14. #14
    He also hooked it up to a diagnostic machine and it showed no codes.

  15. #15

    Re: Fouling out spark plugs

    need to check the timing!!! how many miles is on he engine? you can also get a cylinder leak down kit and test each cylinder for leak down (its diefferent than a compression test) wil show you if you have leaky valves or stuck valves. but if the timing is too advanced, or retarded then the plug will not fire at the right time to burn the fuel like its suposed to. could be caused by a really loose timing chain, or if its not computer controlled timing then it can be adjusted with the distributor and an advanced timing light (so you know exactly where your timing is).

  16. #16
    Quote Originally Posted by josh94yj
    need to check the timing!!! how many miles is on he engine? you can also get a cylinder leak down kit and test each cylinder for leak down (its diefferent than a compression test) wil show you if you have leaky valves or stuck valves. but if the timing is too advanced, or retarded then the plug will not fire at the right time to burn the fuel like its suposed to. could be caused by a really loose timing chain, or if its not computer controlled timing then it can be adjusted with the distributor and an advanced timing light (so you know exactly where your timing is).
    Has 139k on motor. I will get timing checked out. Hopefully it's not nothing serious.

  17. #17

    Re: Fouling out spark plugs

    139 isnt a whole lot really, so i hope not too!!! Best of luck! lets see its an 88 right? is it carb or TBI?
    94 YJ 4.56 gears, Detroit lockers front + rear, hi flo water pump, Be Cool Polished Alumin Radiator, Random tech Cat, Cherry Bomb mufflers, Hooker Header, fucntional cowl hood, elec fan, 62mm tbi and spacer, Comp Hi Energy 4x4 Cam, Hi volume Oil pump, Jet stage 2 chip, Cold air intake w/K&N filter, SYE, DUI LiveWires + cap n rotor, NV4500 trans, 33/13.50/15 Pitbull Rockers, American Racing 15x10 Wheels, KC Daylighters, all Stainless, Delta H4 headlight conversions, 140 amp alt, etc

  18. #18
    TBI. Yes 88

  19. #19

    Re: Fouling out spark plugs

    ok, well that throws out carb adjustment as a possibility thinking it could be timing, also i would check the AIC and TPS, more so the AIC but still should not cause the over fueling but ya never know for sure. might have something to do with EGR system, theres a lot of possibilites, however, it seems to me that timing would be the most obvious culprit here. does it diesel at all when you kill it after its good and hot, or do anything funny like that?
    94 YJ 4.56 gears, Detroit lockers front + rear, hi flo water pump, Be Cool Polished Alumin Radiator, Random tech Cat, Cherry Bomb mufflers, Hooker Header, fucntional cowl hood, elec fan, 62mm tbi and spacer, Comp Hi Energy 4x4 Cam, Hi volume Oil pump, Jet stage 2 chip, Cold air intake w/K&N filter, SYE, DUI LiveWires + cap n rotor, NV4500 trans, 33/13.50/15 Pitbull Rockers, American Racing 15x10 Wheels, KC Daylighters, all Stainless, Delta H4 headlight conversions, 140 amp alt, etc

  20. #20

    Re: Fouling out spark plugs

    any backfiring issues? or popping through the intake while trying to start it? (which is also pretty much a backfire but without the fire lol) if so then those are obvious signs the timing is way off
    94 YJ 4.56 gears, Detroit lockers front + rear, hi flo water pump, Be Cool Polished Alumin Radiator, Random tech Cat, Cherry Bomb mufflers, Hooker Header, fucntional cowl hood, elec fan, 62mm tbi and spacer, Comp Hi Energy 4x4 Cam, Hi volume Oil pump, Jet stage 2 chip, Cold air intake w/K&N filter, SYE, DUI LiveWires + cap n rotor, NV4500 trans, 33/13.50/15 Pitbull Rockers, American Racing 15x10 Wheels, KC Daylighters, all Stainless, Delta H4 headlight conversions, 140 amp alt, etc

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