isuzu engine runs rich

1995 Isuzu Rodeo, 81K miles, automatic is running rich. Black smoke from tailpipe. No check engine light. Has anyone had a similar problem? Please reply.

Scan it even if you don't have a CEL.

How old are your plugs? Aside from running rich, is it running OK?

81K miles....THAT'S IT???? :smokin: :smokin:

WOW! That truck's a BABY....

Check your O2 sensor, these generally do not go until you're over 100k, but you have age playing a factor here too.

Also, give a check on your fuel filter, if it's clogged it could cause issues.

o2 sensors can get weak and not set a CEL. Usually replacing those will take care of it.

I'm not so sure about that. If the o2 sensor has stopped switching and is sticking at the lean side, it would certainly throw a code. Later OBDII cars can even detect when an o2 sensor starts to become 'lazy' or not switching fast enough.

I suggest reading the plugs. I suspect a leaky fuel injector. Pull each plug and if one of them has black sooty crud on it, you've localized the problem to one cylinder. If they are all black and sooty, then there is something else going on. Maybe a bad fuel pressure regulator. You can get a cheapy fuel pressure gauge at Harbor Freight that will attach right to the schrader valve on the fuel line.

I'm not so sure about that. If the o2 sensor has stopped switching and is sticking at the lean side, it would certainly throw a code. Later OBDII cars can even detect when an o2 sensor starts to become 'lazy' or not switching fast enough.

Its actually pretty common for 02 sensors to be off without throwing a code. Even on OBDII systems. I replaced mine a few months ago (100k miles) and my mileage went up, exhaust smells alot better, and my tailpipe isnt so black. Others on the boards have had the same experience.

New spark plugs and fuel filter. Replaced part of exhaust that was leaking. Engine runs good at low RPMs, problem starts when you step on the gas. At that time you can see the black smoke coming out of tailpipe. Otherwise, it seems to run fine.
The car shows no check engine light. Stay tuned for updates after this weekend. :)

How did those old plugs look?

Faulty coolant temp sensor or O2 sensor? Bad FPR?