1987 4cyl 2.0 Black smoke, poor mpg

[bdclover]

Recently started driving a 1987 Chev Cav (vin 1) 2.0 liter 4 cyl. that had sat for a year. First time we had to jump start but ran great, for a couple of weeks. Then problems. 1st round one of the coils went bad, had it replaced as well as plugs. Ran good for about 2 weeks. by good I mean 25 mpg (143K miles on the odom) Then one morning engine light comes on, exhaust sounds different, and black smoke out the rear. Changed spark plug wires and pcv valve--no change. Tried to hook up code reader, engine light stayed on no codes flashed. i keep cleaning the plugs about every 3rd day. Getting 5 mpg. It also can be very sluggish and other times runs smooth but still bad mpg.
I have a parts car. Should I try replacing the computer or ECM? Found the computer where is the ECM?

[FormulaLT1]

I would have the car's oxygen sensor scanned and monitored to see if maybe its causing it to run real rich.

[public]

You are running rich. ditto the above advise and I would try some fuel injection cleaner (lots of it). Good Luck.

[noshun]

Originally Posted by public

You are running rich. ditto the above advise and I would try some fuel injection cleaner (lots of it). Good Luck.

Yup rich hence the black smoke (unburnt fuel) it's sinlge point injection right? take off the air cleaner and with the car running see what the injector is doing, is it spraying a nice equal fan as a fairly fine mist or is it pouring out. could even be a bad inj!

[Three_Fingers]

Running too rich- I would check the coolant temp sensor wiring and then the sensor itself first.

Also check the MAP sensor and O2 sensor. (You can substitute known good ones to check these-but inspect the wiring and plugs to them first. If the ECM can't get the info from them, they're worthless even if they're good.)

Temp, O2, and MAP are responsible for fuel delivery.

If it black smokes bad when stone cold-forget about the O2 sensor-it doesn't do anything at all until it reaches 600 degrees so that's not the problem.

Temp is more likely the culprit. It'll prolly be in the end of the head on the #4 side. Down low. Easy to replace. It'll cause immediate rich mixture if it thinks the coolant is at -30 degrees and it's really only 30 degrees out.
MAP sensor will also cause rich running due to thinking it's at a higher altitude than it really is at-but you'd notice an ignition timing change as well for altitude compensation.