Hello, again. Been busy helping family the past month or so. Car (1990 240) still doesn't run right. But I have narrowed it down as to what is wrong. Before I disconnected the battery for diagnostics earlier today, it was showing codes for fuel injector faults and a short in the TPS circuit. I finally got around to checking the circuit resistances and here's what I have.

From one side (pin 2 on the Fuel Control Unit connector) I have .16 ohms at Idle and 22,700 Ohms at full throttle from the TPS. From the other side (pin 3 on the Fuel Control Unit connector) I have open at idle and .16 Ohms at full throttle. My only concern is that my manual says that pin 2 should be open at full throttle. The fuel injector resistances are, according to a trusted mechanic I took the car to before, fine.

If the resistance numbers on the TPS are in the norm, then I believe I need a new Fuel Control Unit. I've been told that my Control Unit (part number 0 280 000 561) can be interchanged with a better unit (part number 0 280 000 951). Is this true?

Edit: The trouble with it is that the car doesn't want to move. It runs a little rough at throttle when sitting in Park/Neutral. When you try to move at anything more than 1/3 throttle it bogs down heavy and struggles to go above 35-40mph. The further you push the pedal down, the worse it bogs.

 

Does it run better after it warms up?

 

Oddly enough, yes. It gets a little better but it still doesn't operate at full power. I've already changed damn near everything involving the fuel/intake system trying to track this problem down.

 

Have you tried the Engine temp. sensor (some call it the engine temp. sensor)? I changed that on a car and it ran a lot better, especially when it was just started. Easy to change if you've got a fist the size of a 5 year old.

 

I tested the sensor resistance before. Unplugged the Control Unit connector, measured resistance from there. Then ran the car until it was warmed up, and then checked the resistance again. Problem was that I couldn't get an accurate measure of what the engine temp was for the warm reading. So accuracy of the resistance readings was questionable. Though they did match up with what was normal. I can do it again to make sure, but like I said, I can't get an accurate temp reading beyond "the temp gauge was at three-quarters when I shut it off".

 

Just got done testing the temp sensor. At ambient temp it's measuring 2,700 Ohms and at running temp it's reading 310 Ohms. So everything seems fine there. Those measurements were taken the same way as before from the Fuel Control Unit wire harness connector. I can't reach the temp sensor from under the hood without taking off the throttle body.

This leads me back to the control unit being bad. It was throwing codes for bad injectors when they all work fine and it was throwing codes for a shorted out TPS when the TPS is not only new, but has good wiring.