I was measuring voltages and signals on some of the connectors that go to the MAP, TPS, MAF, MAP, & TPS. The 5vdc is there, but when I measure the ground back to the main terminal on the negative cable of battery it measures around 35 Ohms.

I would expect something around 1-2 ohms, but 35? Something doesn't seem quite right.

When I make a measurement with my scan tool, the Air Intake temp is frozen at 303 degrees. It's 75 degrees outside, so I know I'm not on Venus.

Could it be that the ECM is dead? Maybe the bad ground is causing all my ignition problems.

Where does the main engine harness get connected to ground?

 

Note wiring harness ground in the same bundle as the knock sensor wire:

1995 Z28 A4 Engine Harness

Those are all 2-wire circuits. They are not relying on the engine as a ground. The important thing is that you get 5V between the reference wire from the PCM and the ground wire from the PCM at each location. Not 5V from the reference wire to the battery ground.

The inlet air temp sensor is a 2-wire circuit. The PCM is reading a direct short = 0 resistance (or close to it) and showing the temp as 303*F. Did you check that circuit for 5V with the harness connector disconnected from the sensor? Did you measure the resistance of the sensor and compare it to Shoebox's data:

4th Gen LT1 F-body Tech Articles

 

Injuneer,

Thanks for the quick reply. I did measure at each connector 5V & gnd, and got 5vdc every time. I measured from each connectors gnd to battery ground and got the 35ohm reading. That's what had me concerned. But maybe the grounds are protected.

The temp reading your referring to are the engine coolant temps, not the air inlet temp. I'll check the wires from the connector to the main harness connector at the ECM. If there's a short, that's not good. What would it read if it were open????

Thanks again, I really appreciate your help here. This thing is driving me nuts.

 

Read my post... I realized about 10 seconds after I posted that you meant IAT and corrected it. In any case both are 2-wire sensors and they both get 5V at the harness (disconnected) and use a thermistor with the values show in Shoebox's table.

 

Injuneer,

Didn't read the last line on that subject. I stand corrected. I didn't read anything across the two leads on that sensor's connector. Don't think I'll be reading 5vdc at that connector, maybe dc current instead. Wouldn't the ECM use the resistor in the sensor as the current adjuster?

Could that be the reason why the car runs so rich???

I am surprised that it didn't throw a code.

 

Sure enough, the wires going to the IAT sensor were bad in the leads coming up to the sensor. Replaced the wires from the connector to the harness behind the alternator.

IAT temps are now reading normal. I'll post the live data later, to see if anyone can tell me if this thing is running normal.

Thanks Injuneer for the guidance.