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!
Fouling out spark plugs
- Thread starter tbfreeman
- Start date
josh94yj
New member
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
josh94yj
New member
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!!
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)
Bad vacuum would yield a very noticable drivability issue, not sure on the correlation to fouled plug(s)
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.
josh94yj
New member
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).
josh94yj
New member
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?
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?
