I believe either the ground on my PCM is bad or some sort of reference circuit to many sensors is bad. I have a 1994 2.3L ranger 4x2. Let me explain.
I bought an OBD1 scanner, and it spat out a ton of codes even ones that don't necessarily make sense. But the gist is that my MAF, ETC, ITC, TPS, EGR etc etc are all bad (which seems unlikely). So I believe the wiring common to all these is an issue somewhere. I was doing the Key On Engine Off test first and some codes pertained to the engine running. The issue is very similar to this thread:
"Bad Ground/Power Connection; PCM? - The Ranger Station Forums"
So, I started with the TPS. In his case splicing in a new ground worked. However, I'm not receiving any high idle, high rev problems. The truck is sluggish without power (maybe normal - this is my first 2.3) and does this surging thing.
I tried back probing the TPS following the instructions in this thread (Ford Explorer - Ranger TPS Test Procedure | Ford Explorer and Ford Ranger Forums - Serious Explorations
) and let me tell you that's FUBAR. The TPS cycles from -0.1V to -0.56V, yet the truck is still driveable. Pulled the plug and VREF (brown/white wire) reads 5.0V when grounded to the battery. Now this other thread (tps ground problem | Ford Explorer and Ford Ranger Forums - Serious Explorations
) on the next to last post by X-North titled "The Solution" suggest measuring the voltage between the VREF (brown/white wire) and wiper (grey/white) wire. I got 4.85V; he's saying you need 5.0 and if you don't 'get 5.0 then it's the grey/white wire that's the problem. The grey/white wire to battery is roughly 0V and the red/grey wire (signal return) is 5.5V grounded to battery. X-North, then suggest checking the connection behind the alternator to see if the same 4.85 V exists between brown/white and grey/white. If so, he says replace grey/white back to PCM.
One question I have is which connector is he talking about. The one directly behind the alternator looks difficult to get to and unplug, especially the PCM side.
I have also checked the different grounds by placing a probe on battery terminal then touching rings/wires/bolts both on the ground by the battery and the one by the computer. Both showed continuity, but on the OBD1 reader I had to jumper the small plug to the battery because there was no ground there and the reader wouldn't get the codes without a proper ground.
Any suggestions? Why is the TPS so far out of range? What do all these sensors have in common? Is the grey/white really bad? Is it the ground? Thanks for any help, and please let me know if I can be more clear or provide more info.