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fouled plugs

J

jefftrucker12

NAXJA Forum User
Location
arizona
just got a 89 cherokee and am going to build a buggy. it wont be street legal so wont have to pass emmisions but want it to run ok. it smoked blackish greyish smoke out the tailpipe and though it might need a tune up. i took out all the old plugs and they all had black soot on them. i went to auto zone and got new plugs cap and rotor. i put them in and today when i started it up it ran about the same. i took a new plug out that i just installed and it had black soot all over it after running for 15 seconds. what would cause this. the motor is supposed to be a ho 4.0
 
Running way too rich, if it is indeed soot.

Shot rings can cause oil fouling. Tailpipe smells are different for the two. If it is pumping that much oil, the rear window should have a film on it.
 
Most common reason to run way too rich is the O2 sensor, followed by the MAP, then by fuel pressure too high. If it is a little too high, your engine temp sensor could be shot, but that normally won't cause what you are describing.

After thinking about it, the O2 sensor does not contribute to the engine control until the engine warms up. My bet is fuel pressure or MAP. If it were only one or two cylinders, I would be inclined to say injectors. The injectors are the original ones, right? They may have been swapped for larger ones by some dufas.

In theory a plugged CAT could cause it to run to rich but your power would be really crappy.
 
Last edited:
i just talked to the guy who i bought it from and he said that he replaced the injectors, oxygen sesnor and the fuel regulator but not the m.a.p.
 
The MAP or the TPS could cause the problem, but the computer should be able to compensate for both, at least to the point to keep it from running that rich. Check the CAT.
 
Ask around on here. If it is a manual tranny, I have one for $30 plus shipping.
 
Sounds like Miller time.party1:
 
got a new map sensor and cleaned all the plugs and it idles without smoking and only smokes if you really hit it. the smoke is grey?? its really not all that bad though
 
Since it was running so rich for so long, a can of BG44K in the fuel might be in order. The stuff works miracles.
 
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