I have an 83 CJ7 with a freshly rebuilt 4.2L/4.0L Head combo with less than 500 miles on it. It has a new distributor and O2 sensor since the rebuild and it has the earlier MPI kit installed. I'm using the cooler plugs as suggested by Hesco.


The problem is I have this funky smell coming from the exhaust or jeep and I find the engine missing at idle. The smell is bad enough for my apartment manager to ask me to use a different entry into the complex.

I pulled the plugs and they all have carbon on the "Base" of the plugs. The carbon is not on the Porcelain or electrode(s) but on some it's creeping up the ground electrode.

Is this engine running rich? How can I get rid of the funky smell? Could the Charcoal Canister be bad?

Thanks in advance

first take it somewhere to get the numbers read. don't guess. you might have just got a tank of bad gas. if you suspect a rich condition and the electroincs seam to be good. check the pressure on the fuel rail with the jeep on and off. you want to make sure you dont have a leaky injector.

Hey Sunder,

I've been to 3 places so far.
The engine rebuilder. I told him about the missing and showed him the plugs and he said "run it".

Before that I went to a place that does dyno testing and they said if anything it's running lean and to have someone adjust the timing with a DRB II. I went to them to be sure I didn't have a leaky injector(s).

Lastly I went to a place locally who specializes in CJs. They've done many, many, mpi kit installs. He put it on the DRB II and said I should be tickled. He said the missing could be due to the cam they put in (brand new stock cam).

Either these guys are all idiots or I'm stupid cus I don't believe I should be having this funky smell. Add to that, I don't believe I should have carbon build up on the base of the plug.

Am I wrong?


Also, regarding the testing of the leaky injectors. IIRC, you want me to test the pressure at running and shut it off. Then watch and see if the pressure decreases significantly. If it does then I have a/some leaky injectors. Correct?

If so I did this test a while back and it didn't reveal any difference in pressure. I will do it again though to be sure.

Thanks,

Put a cat on it! That should take care of the smell. Is it a "sulfer" smell?
As for it being rich, do you see faint traces of BLACK smoke while it is running at a steady rpm? If only when mashing on the pedal that would be ideal.
Big JIm

Hey BigJim,

Got a cat on it and had it checked by a muffler shop when I had the 4.0L exhaust manifold fitted to the tail pipe. No traces of black smoke at idle. What about the carbon around the base of the plug. Is that normal?

What color is the porcelain on the plug? If it is black or "near" black is when you'd be too rich. If tan, brown or light grey I'd think they were OK.
Back to the cat... THERE lies the smell. You need a larger cat, or at least another cat. The 350 chevy trucks in the 90/91 era came from the factory with too small of a cat and they had a potty smell... The fix was a longer cat, and it worked. Do you have the ENTIRE FACTORY exhaust? If the cat was advised by a local muffler shop, I'd go to them with the thing hot and smelly! Get em to give good converter.
Big Jim

do you still have the stock 4.2 cat?? it could be inadequate, but you say it is missing. soo.... it has to be REALLY reach to miss or really lean. if you aren't seeing any black smoke i bet you are lean missing. you could get one of those cheap AFR gauges at autozone or hook up a voltmeter to the O2 sensor to see what it's feeding back. if the voltage is correct at the O2 sensor it might be bad. the best bet is to get some 5 gas readings though... do you have a JC or regualr college around?? they'd probably take a look at it for you for free and they'll have a 5 gas machine. also a lean miss can overheat the cat and make it burn out. first off i'd get some numbers. high CO means rich Low or 0 CO means lean. if it's only started in the past coulpe hundered miles and hasn't done it before, it means some part has failed. don't let them bursh you off, saying its normal for a new engine to miss.

Hey guys,
Yeah, I believe the Cat is stock for the 4.2. The porcelian on the plugs are white-ish with a some orange color.

I just learned that Unleaded fuel causes black around the base of the plug.

Sunder, what's a 5 gas machine? The shop I mentioned above put it on a machine testing gases at the tail pipe like a smog test machine. He said if anything it's running lean. Also, I had another mechanic look at the jeep for a drivetrain issue and I had his friend, another mechanic look at the plugs and, without me telling him anything, he had the same comment, "It might be running a little lean".

If it's running lean what can I do? The last time I tested the fuel pressure at the rail it was within Hesco's specs. Especially at idle. The fuel pump is quite new. The only other thing I can do I guess it get the adjustable fuel pressure regulator from Hesco which is somewhat expensive.

What will a lean running engine do to the engine life? Would a lean running engine cause it to smell funky?

Thanks,

if the engine is lean missing at idle, it will be disconcerting but not too much of a problem, but only if its at idle. if it miss at WOT or just driving down the road it will melt the cat down. the miss is probably causeing the smell. when it misses it shoves unburnt fuel down to the cat, cuaseing it to get REALLY hot and may have melted it down so that you look like you have a cat, but you don't really. does it pass emmissions(besides idle)?? does your jeep have an exhuast leak? a leak in front of the O2 sensore will cause it to run poorly. An intake manifold will make it run lean too. take your propain bottle and hunt around for intake leaks. do you have an adjustable TPS. if it is trying to run off idle it might be getting too lean.

as for the funky smell... i'd have to smell it. funky isn't descriptive enough.

A five gas analyzer is basically a smog machine. it measures O2 CO2 CO HC and NOX. you CO level is basically your Air-Fuel mixture indicator. NOX is combustion temp. the others follow tghe CO and compustion temp around.

For starters i would make sure that the fuel pressure is at spec at idle, make sure your TPS is proporly adjusted, and do a basic tune up. if it still is lean missing at idle, check for intake and exhaust leaks, then go get some number at a cheap smog check staiton. sometimes those guys who arn't busy will do an unoffical numbers for under 20$

You said:
The problem is I have this funky smell coming from the exhaust or jeep and I find the engine missing at idle. The smell is bad enough for my apartment manager to ask me to use a different entry into the complex!

Ok the problem IS the CAT! Get the correct one and the smell will stop.
Everything else you have said makes me believe the engine is running up to specs.
The plug description is very good.
You need a cat that will handle the new stuff.
Big JIm