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Fowled spark plugs

Sullie

NAXJA Forum User
Location
el paso tx
1988 jeep xj 4.0L manual transmission...

Tuned her up a few weeks ago, brand new...
fuel filter
Air filter
Sparks plugs
Wires
Rotor and
Cap...
Now every few times I start it is have to pull the plugs and clean them so she can start...

Everyone I pull is fowled up black and smells of fuel, I know creat spark, gas go boom...
But what could be causing it to fowl up so quick?

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Pull the vacuum line off the Fuel Pressure Regulator. If there is gas there, the FPR is shot and leaking fuel into the intake.
 
I found it online
Here it is for everyone else
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Is it dry on the vacuum side? Check the injectors for leaks?

Once you rule out fuel leaks, look at the exhaust manifold for cracks in the welds. Those cracks can pull in enough air to fool the oxygen sensor. After you rule that out, throw money at the oxygen sensor.
 
Is it dry on the vacuum side? Check the injectors for leaks?

Once you rule out fuel leaks, look at the exhaust manifold for cracks in the welds. Those cracks can pull in enough air to fool the oxygen sensor. After you rule that out, throw money at the oxygen sensor.

Got a better idea, Test the O2 sensor with a volt meter per my old O2 sensor test thread in this forum. But it sounds like it is flooding and running rich, so I like the FPR leaking into the vacuum line, and possibly and O2 sensor issue. But it could be a bad ground since its Renix, 1988, and or a IAT temp sensor that is super dirty or defective, which can be tested with an ohm meter. Not likely to be an injector issue etc since all the plugs are fouled, but definitely running rich and possibly flooding.
 
There is no fuel in the vacuume line that I can see.

Searched for your o2 sensor thread, couldn't find it.
Not real sure where the sensor is located or how to test it.

Is there anything else that could be causing the fouling, maybe TPS?

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I know you installed new plugs: What brand, verify the gap was @ .035"?
 
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I have OMIX-ADA plugs, wires, cap, Rotor, filter...and gap is .35 on all plugs

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Running rich

Figured I'd start a new thread

1988 XJ 4.0L

Running rich, fouling spark plugs...
Dry, black residue on plugs...
What could be issue, how do I check and where is the part located?

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Spark plugs was kind of an afterthought.

You would think a plug is a plug, but our RENIX Jeeps do better with the regular ol' copper core, Champion or NGK plugs. I was running Champions, but decided to try the NGK ZFR5N that Cruiser54 recommends. So far, the Jeep runs fine and the plugs clean off.

For some reason, the platinum plugs don't do so well. Maybe someone else can provide that insight.
 
Many of us have good luck with some platinum plugs. I have 4 cyls on my 290,000 mile Wagoneer XJ that run 50,000 miles and the plugs still look new, but the 2 cylinders with worn leaky valve guides must have the NGK FR5 plugs or they foul badly. I found out the FR5 is a wee bit hotter plug!!!! My 89 ran for 10 years over 100,000 miles with the single tip platinum plugs and got great mileage and power. The 89 has awesome compression, the 87 is near the OEM low spec limits on compression. I have never tried the ZFR5N plugs. They were designed for the late 90s HO engines and HV coils. But Cruiser54 says they also work great on his Renix rigs. I also run 20W50 Dyno oil sometimes with Lucas on mine. Fouling rate varies with the oil mix and type.

I have never heard of an Omix-ADA spark plug???

O2 test thread is here:
http://www.naxja.org/forum/showthread.php?t=1012701&highlight=oxygen+sensor+test

Spark plugs was kind of an afterthought.

You would think a plug is a plug, but our RENIX Jeeps do better with the regular ol' copper core, Champion or NGK plugs. I was running Champions, but decided to try the NGK ZFR5N that Cruiser54 recommends. So far, the Jeep runs fine and the plugs clean off.

For some reason, the platinum plugs don't do so well. Maybe someone else can provide that insight.
 
Vacuum line to map sensor ok? Or possibly a bad map sensor?

Good point, but I am curious if the vac line is even needed for starting? I know the MAP sensor is critical for starting. But there is little vacuum while cranking I think? I recall testing that years ago, what needed to be connected to start a Renix. The vac line is super critical for acceleration and deceleration, backfires during acceleration when disconnected, but runs at idle disconnected. I use to have a loose one at the throttle body years ago.
 
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Starting not really. Computer takes a baro reading at key on. However once it's started it needs to work, or it'll foul plugs quick.

Even in closed loop using the O2 sensor? But I guess with out the MAP vac signal it never gets to closed loop?
 
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