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Old 07-06-2004, 07:12 AM   #1 (permalink)
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What causes spark plugs to foul??

This may be better in the newbie forum, but this engine has me stumped.

It is a jeep 2.5l 4 cylinder. It was running rough, so i put new plugs in it. It started up and idled a little rough but ran good at hight speeds. I took it for a 2 or 3 mile drive. It had no power and by the time i got back with it, it was running very rough.

I took out the plugs. 2 of them still had white insulators, but the other 2 were covered in black.

This means that they are probably fouled right??

Any ideas what would cause this??

Any ideas on how to fix it would be appreciated!!

Thanks in advance.
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Old 07-06-2004, 07:19 AM   #2 (permalink)
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covered in black I do believe denotates oil fouled*. Meaning excessive oil consumption. could be bad valve guides, could be bad rings.. try changing your oil, it could be overly diluted with gas further causing the issue. (thinner oil gets past valve guides and the like easier)

if you still have problems, there are a couple bandaids.. hotter plugs, or the HELP! section has things dealie-ma-bobbers that extend the spark plug out of the holes to keep oil off of it..

*-depends on what kind of black.. sooty black can be rich mixture.. wet-ish black can be oil..
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Compassion has a maximum effective range of what, zero fucking meters?

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Old 07-06-2004, 08:00 AM   #3 (permalink)
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Where they oily or was the black like soot?

If it is like soot your rig is running too rich(too much fuel in the air/fuel mixture).

Rough idle + rich mixture = I would look for a vacume leak first.
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Old 07-06-2004, 08:07 AM   #4 (permalink)
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thanks for the ideas guys, it does seem to be more of a sooty black and it does smell bad going down the road, but i thought that might because the cat has been removed.

I will definately change the oil and look for a vacuum leak!!

Could anything else cause it to run rich??

It is computer controled (93) and it is not showing any codes!!

Thanks again.
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Old 07-06-2004, 08:38 AM   #5 (permalink)
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map sensor?
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Compassion has a maximum effective range of what, zero fucking meters?
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Old 07-06-2004, 08:46 AM   #6 (permalink)
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try this link
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Old 07-06-2004, 08:52 AM   #7 (permalink)
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How many miles?

How bout a faulty O2 Sensor. They are only "good" for around 70,000 miles. If you can only afford to replace one at $70-100, replace the one on the exhaust manifold.



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Old 07-06-2004, 10:02 AM   #8 (permalink)
 
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My question is why would two plugs be white and two be black. A sensor problem should cause an issue accross all cly now just two. How white are we talking here? bright bone white?? Or can you see that they are starting to go to a light tan from use?

Change the oil and see what color it is, is it grey and runny? Does it smell of fuel or what?

What color is the smoke out the back?? Blue, white, black??
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Old 07-06-2004, 11:30 AM   #9 (permalink)
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It has 110k on it.

If it was a faulty o2 sensor shouldnt the "check engine" light be on??

The 2 good and 2 bad is what has me stumped also!!

From reading the link that Ian gave, maybe those 2 injectors are faulty?? not spraying correctly??

The jeep had been sitting for 2 years!!

Any other ideas??
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Old 07-06-2004, 07:56 PM   #10 (permalink)
 
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check fuel pressure and see if it leeks down after you turn it off
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Old 07-06-2004, 08:19 PM   #11 (permalink)
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if its been sitting for 2 years, id check out those injectors first. thats a long time to sit.
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Old 07-07-2004, 05:57 AM   #12 (permalink)
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Ok, i took the spark plugs out again last night.

3 of them looked ok, but the 4th one was wet and smelled like gas.

when i checked the oil, it was overfull and smelled and felt like there is gas in it.

I am thinking that the 4th injector is bad, any way to tell for sure??

they are $80 for a new one!!
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Old 07-07-2004, 06:27 AM   #13 (permalink)
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Quote:
Originally Posted by DieselYJ
thanks for the ideas guys, it does seem to be more of a sooty black and it does smell bad going down the road, but i thought that might because the cat has been removed.

I will definately change the oil and look for a vacuum leak!!

Could anything else cause it to run rich??

It is computer controled (93) and it is not showing any codes!!

Thanks again.

I don't know about early efi heeps, but I do know that other EFI mopars have an o2 sensor pre and post cat. So if you removed the cat, that reading is going to be fawked... Might wanna start there.
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Old 07-07-2004, 06:57 AM   #14 (permalink)
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The PO removed the cat, but i dont think that this jeep had the 2 o2 sensors, there are no loose pigtails back there anyway.

But i will look again tonight just to make sure that it hasnt been cut out or something like that.

If it was removed, wouldnt the "check engine" light be on??

thank again
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Old 07-07-2004, 07:18 AM   #15 (permalink)
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I think your going in the right direction with the injector. If it was a vacuum leak or O2 sensor or MAP it would effect all the plugs. It sounds like two of em were stuck open and one unstuck itself. I dont know Jack Squat about Jeep injection systems, What controls the injectors?

I would Get a book, hell even those haynes manuals are better than nothing. I'll bet there is some way to test the injectors.
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Old 07-07-2004, 07:23 AM   #16 (permalink)
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its a 93 there wont be an O2 behind the cat. thats OBD2 stuff.
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Old 07-07-2004, 08:11 AM   #17 (permalink)
 
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Quote:
Originally Posted by bansheeman1
check fuel pressure and see if it leeks down after you turn it off
this will tell you if your injector is leeking down
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Old 07-07-2004, 08:18 AM   #18 (permalink)
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ok, so it looks like i will go to the parts store and get a fuel pressure gauge and also take a look in the haynes and see if i can test the injectors.

So if one is leaking down, the fuel pressure will slowly drop when i shut the jeep off right??

Thanks again, i will figure this out!!
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Old 07-07-2004, 08:30 AM   #19 (permalink)
 
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It should hold pressure for good while

Most parts houses well rent a pressure tester for just the deposit
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Old 07-08-2004, 06:28 AM   #20 (permalink)
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Well i got the gauge last night but did not have time to play with it.

Will be doing that tonight, let you know tomorrow!!!
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Old 07-08-2004, 06:33 AM   #21 (permalink)
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Quote:
Originally Posted by DieselYJ
Well i got the gauge last night but did not have time to play with it.

Will be doing that tonight, let you know tomorrow!!!
Hopefully you have a test port on your fuel rail. The fawktards in DC decided to NOT put one on my wifes 97 TJ so I can't do a leakdown test without buying a $$$$ tester. (Haven't found one less than $150-200 yet)

If it's an injector, you can check out aftermarket. OEM replacement is $80, I've seen aftermarket going for $40 or so. I think those were Summit brand, don't know if that's a good/bad thing.



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Old 07-09-2004, 06:27 AM   #22 (permalink)
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Well it does have a port and i checked it out last night.

The pressure is right were it should be and it did not leak down very much at all 3 or 4 psi in 30 minutes.
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Old 07-09-2004, 06:52 AM   #23 (permalink)
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Quote:
Originally Posted by DieselYJ
Well it does have a port and i checked it out last night.

The pressure is right were it should be and it did not leak down very much at all 3 or 4 psi in 30 minutes.

Compression test or cylinder leakdown test?
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Old 07-09-2004, 07:55 AM   #24 (permalink)
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It was on the fuel pressure, so i guess you would call it a leak down test.
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