Running Rich - 92-4.0L

I have a 92 Wrangler, 4.0L that is running real rich. Plugs go black, black smoke from exhaust.

I put a new O2 sensor in a month ago, but it is still running rich. I have gone through and cleaned out the TB, and TPS & AIC sensors, still rich.

What else could cause this?

Reply to
Les
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Cheap ones first.

- loose or broken vac line to the fuel pressure regulator? That results in too high a fuel pressure under normal operation.

- Or too low a heat range on the plugs. If they are running cold they will soot up.

Bad coil/weak spark that's not igniting each charge and letting some of the fuel through. leaking injectors (but usually that's only on one cyl). Clogged cat can result in backpressure problems.

Any fault codes?

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Reply to
DougW

Intake air temp sensor.

Spdloader

Reply to
Spdloader

A dirty air filter?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >
Reply to
Mike Romain

Nope it's new

Previous Owner cut a hole in the cat and clean out the guts. It does leak a little, and I need to replace or bypass with a straight pipe

No Codes

Can these be tested with a meter?

Reply to
Les

Yes. they are just temperature sensitive resistors. (both mat and engine temp)

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Reply to
DougW

When the sensor goes bad, it reports a cold condition that causes the system to go "full rich". Doesn't log a code, the computer just stays in cold start loop. Very common on GM 4.3 engines too. I don't have the operational parameters for testing with a meter, but someone here will.

Spdloader

Reply to
Spdloader

Cool, but its time to talk dummy language...

How does that table convert to an Ohms reading? My gauge (old needle type) read from 0 to 1K.

Great Web Site!

Reply to
Les

The table is in ohms, 0-1k is 0-1000. There is probably a scale setting on your meter. Look for 10k or 100k. Worst off you can get a cheap digital meter at RadioShack, AutoZone, PepBoys, etc.

Reply to
DougW

You 'really' don't want the VOM anywhere near the computer sensors. The load the meter puts on can fry computer circuits. Same for a test light.

It's time to step up to a digital multimeter....

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06
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Reply to
Mike Romain

Like a Fluke or it's equal. Spdloader

Reply to
Spdloader

I agree; the engine's probably stuck in open-loop mode. Older designs like this often have 2 engine temp sensors: 1 for the guage, 1 for the computer; if the computer temp sensor stops working for whatever reason, this will keep it open, as will bad O2 sensors. A really bad IAT will too. Older computers wouldn't set the MIL either.

I have to wonder, if the cats were tampered with, if the owner also just pulled/disconnected the O2 sensors as well, which would cause this.

Reply to
Outatime

I know I just stepped in on this one and it may have been suggested already, but I had a leaking exhaust manifold gasket. The air coming in (yes it did that) makes the O2 sensor think the engine is running lean and tells the computer to richen (is that a real word?) the mixture. After replacing the gasket and cleaning the sensor, my jeep ran better and mileage came back up. Simple fix. Well simple parts, but PITA to do. If you are having a whistling sound at highway speeds when feathering the gas pedal, that is a sure sign of it, that being said if it goes on long enough the whistling will go away. Got the t-shirt. Rich Harris

Reply to
Rich

"Enrich."

Earle

Reply to
Earle Horton

Reply to
Rich

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