we have an 84 240 motor in use as a power unit for a small sawmill. it runs rough and puts out black smoke.
i've pulled the control unit and amm and put both of them in a running 84 240 wagon, and the car runs fine. the orange wire on the amm harness shows 12volts.
while the motor is running i can unplug the amm, and the motor performance doesn't change. this makes me think the control unit isn't receiving info from the amm, or that info is being blocked by something.
anybody have any ideas? i've traced all the wiring from amm to control and it's all intact. i do have some of the pump relay and main relay wiring improvised for the new job the motor is doing. but it cranks up and runs. temperature sensor is good.
thanks
Harvey

Hi Harvey,

If you want to verify the amm is conveying the airflow information, read the output voltage back to the ECU. It should run about 2.5-2.75V thereabouts when idling and up to 4-5V when revved up. With ignition on and no airflow it should be around 1.5-1.7V. I figure you have the book if you traced the wiring, so I won't fetch mine and read out pin numbers.

Other inputs to the ECU that govern injector duration are temp sensor (read at ECU- should be less than 0.2V when warmed up.), cold start enrichment (pin 4 I think looks at starter solenoid), and to a lesser extent the lambda sond.

Don't forget the stuff the computer can't control, like a stuck fuel pressure regulator or blocked return line. The tank and fuel delivery must have been a custom arrangement for your sawmill.

Regards and best of luck.
--
Art Benstein near Baltimore

thanks very much art. I'll check the fuel pressure regulator and return line first, then go through the voltage readings. the tank and main pump just sit on a wooden cradle to one side of the motor.
I could also have the cold start enrichment getting voltage all the time.

thanks very much art. I'll check the fuel pressure regulator and return line first, then go through the voltage readings. the tank and main pump just sit on a wooden cradle to one side of the motor.
I could also have the cold start enrichment getting voltage all the time.