I've swapped an '87 MPFI 2.8 into an '85 Cherokee. I'm trying to find the reason for the coppy, rough idle. I wired up a light to the wires for the check engine light to check codes, but get no power to it. The manual I have shows the check engine light wire to be a brown with a white tracer. I wired a light to that wire and the other end to chassis ground and get nothing. Is there a wire connetion to a certain componant of a MPFI system thatt'l effect this? Any ideas, thoughts???

 

Did you use a computer-safe probe? I've never looked at the wiring diagram for the SES light- I don't know if it can drive a bulb directly, it might draw too much power from the computer.

I'll try to remember to check tonight!

 

The wire that I'm connecting the test light to is the one on the harness plug that plugs into the back of the inst. cluster. My test light is a home made one using the same type of bulb that is in the dash for the check engine light.