Goldpanner

1999 Cherokee, 4.0, 195k miles
It sat for a "while". Replaced oil, oil filter, air filter, plugs, wires, cap, button and coil. Cleaned IAC and throttle body. After two tanks with sea foam still blows black when accelerating. Good power, does not run rough or misfires. Just no fuel economy and smokes.
Any ideas?

jordan96xj

Use a scanner (OBD2) to observe the fuel trim levels. It is probably running rich, perhaps due to an O2 sensor that is providing bad values, or some other condition.

Check engine light on?

Goldpanner

Yes the check engine light is on. My friend checked it and it was the fuel return line error. No O2 sensor faults.
I forgot to mention that prior it running rich my Grandson sprayed the engine with simple green and then hosed it off. Could water have shorted out or damaged an electrical component?

PatHenry

Jordan96xj is a master pro at deciphering the fuel trim level readings. If you get him some specific values he can help you analyze what's going on and help pin-point what the problem is.

Typically the electronics are pretty resistant to simply being hosed off, but anything is possible. You could still have a bad O2 sensor that's just not triggering a code. I would seriously put a scanner on it and get some actual data and follow Jordan's advice.

Goldpanner

Thanks. Will post results.

jordan96xj

Thanks for the kind words PatHenry, but I'm not doing any voodoo magic. Just using the fuel trim values to confirm whether the mixture is being commanded rich or lean and then pointing the OP in the right direction from there. A good OBD2 adapter can be had for about $20 these days, so its something anyone can do. Most of them will also show the voltage levels coming off of the O2 sensor(s), so that is extra helpful. Even on my 96 (first year of OBD2) I can get those data points. There are also lots of videos on youtube explaining fuel trims and how to use the information in troubleshooting.

And yes, it is common for the O2 sensor to be failing in such a way where it does not cause a code for itself. Usually the code will be for running lean or rich (PO17X) type code. Unless the the sensor has lost connectivity, or its heater circuit, which sometimes will throw a distinct code just for the sensor.