Ah, okay, it's the open ECT circuit that tells it to go to "tuneup mode" and not advance. That tells me a lot. Since it's throwing an ECT circuit error, that suggests that when it matters it's failing to advance, and that'd account for it running like crap at speed and under load. I suspect the sensor itself is actually okay (as I mentioned above, about 25k cold), so I'm going to chase down the wiring and see if that's where a/the fault is.

Where does the vehicle speed sensor figure in to this?

 

It doesn't, as far as I know.

It's ENGINE speed that calls for advance.

RwP

 

Exactly. Which is why I'm puzzled at the ECU needing the vehicle speed input, since it doesn't control the transmission.

 

Well, it controls overdrive and lockup (although OD can be defeated with the dash button.)

It also controls cruise on 1990 and up (and I think 1989, but don't quote me on that! I'm not sure when the change occurred.)

There's other things the ECU does besides the advance curve after all ...

Also, on the standards, it lights up the "Upshift" light.

RwP

 

All makes sense.

Now, can anyone tell me what the correct (resistance) range is for the coolant temperature sensor?

 

It's actually in the factory service manual.

RockAuto shows the same part number for my 1988 3.9 as for your 1991 5.2; I've attached the page from my 1988 FSM.

RwP

 

Thanks - I ordered an FSM this morning, should see it in a week or so.

Going to have to keep poking at this thing - the little extension cable thats get it out from under the AC compressor was in rough shape, so I fixed it up and with the engine cold (ambient is about 55F at the moment) the meter says about 8k. That should put it within acceptable range (based on the page you supplied), but the key-blinky is still saying out-of-range (22). I'll probably check it at the ECU pins and/or go for a drive tomorrow and see if it settles down.

 

If you haven't drive it, then it's going to still give the 22 until you reset the ECU or enough drive cycles have happened.

RwP

 

Since this thing is pre-OBDII, I wasn't sure about that. So without the Chrysler scan tool youl just have to disconnect the battery, which should clear every error except for the 12, right?

 

Or drive it a few times, either one.

RwP