'89 D100 V6 running too rich
 

I am attempting to sort out some bugs on my son's '89 D100 V6 automatic. Right now the problem is it appears to be running was too right. I say this as just letting it idle in the garage it blows a lot of black soot through the exhaust pipe. It has throttle body injection, so I do not know what to do to diagnose this.

I did the check code routine and it only flsked a 12 for battery disconnect followed by the 55 end of code.

Can someone point me toward what I need to look for?

Thanks again,

Seeing no codes, you should feel lucky in a way.

I'd start with the obvious and run some injector cleaner through it and give it a long workout at highway speeds.

I have an 1989 "B" and it is dual fuelled (propane). If it does not get used on gas for a while, the injectors tend to "film over" and it runs like a carburetor's accelerator pump needs changing...... a run with injector cleaner fixes it.

Start with air filter ? Possible O2 sensor, exhaust leak ? Bad cat converter ? When was the last tune up ?

How is the truck driven? If its just around town then I would take it down the highway and make sure to keep the RPMs up around 3,000 (that doesn't mean speed, just pick a gear that keeps the RPM high while cruising at 55-60mph). I would also look into throwing in a fuel system cleaner and fill the tank twice with high octane. The high octane will burn longer and more complete helping to get rid of any carbon buildup in the motor.

As TV asked, when was the last time a major tuneup was done (cap, rotor, wires, plugs, spark plugs, PVC, air filter, fuel filters)? Have you pulled the O2 sensor? If it is covered, you will want to replace that and knock on the cat to see if it rattles around. If it does, it will need to be replaced.

The truck has not been driven all that much. I suspect it has sat unused for a year or more. I have added a can of injector cleaner as a starting point. The battery, sparkplugs, plug wires, dist cap & rotor are all new. I have not yet checked the O2 sensor, but will do so and post what I find. FWIW, the exhaust is also new from the down pipe back.
Thanks everyone.