Always with the grounds… Not flaming just kidding.
I agree with you. I am an electrical engineer and what I always say is that if I were to put a black box in the bottom of an electrical panel with wires coming out of it but not connected to anything, most people would blame that box for any and all problems that ever occurred.
This time I'm pretty sure it's the computer though. It's doing some weird things and the diagnostic flow charts given for both problems end up with bad ECM. The MAT, manifold air temp and the cooling temp use the same sensor. This is a 2-wire sensor so it doesn't need a ground. On a cold engine they usually don't even come close to agreeing for the ECM value.
I disconnected the coolant sensor and got -38.7º reading at the ECM, that is correct. I replaced the sensor, put a thermometer in the radiator and started the Jeep. Ambient temp. was about 55º and the ECM gave 55º readings ±a few degrees for the MAT and the coolant sensor values. The thermometer read the same. As the engine warmed up I got.
That the next day, with the engine cool, the ECM reading for the MAT was 50º (same as ambient) but the coolant temp reading was 89º.
I put the ebay ECM in and the temp. readings were normal. The rich/lean flag started alternating between the two, just like it's supposed to and when I took it out on the road, it seemed to be running properly again.
I'm not totally convinced, but I'm getting there.
That 3rdgen.net didn't give me anything. Is this
the one? Here
is one I like.
Mine is an '88, last year with both MAF and cold start injector. I see GM brought back the MAF.
The memcal I'm using works fine, this is an extra. I've got so many extra parts that I can ask, "Do you want to see my other Jeep. Part of it is in this box, part is in that box, part is at my storage site…"
I've replaced so many parts that my old Jeep has become my new Jeep.