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96 XJ stumbles then shuts off when warmed up. P0171

Runnin'OnEmpty said:
Tim gave a good explanation of how the
ASD relay works, with the pcm shutting it
down if a CPS signal isn't detected. This is done
partly for safety in the event of an accident.
(Shuts off the fuel pump.)

Something is failing when it gets hot,
possibly the CPS, fuel pump, or CMP
sensor. I have had two CMP failures on
my 96. Remove it from the distributor
and closely examine the wiring.

Some models will run without a CMP
signal, but apparently a 96 will not.
Click to expand...

CMP as in camshaft position sensor?
I’ve replaced both the crank and cam position sensors - twice. I’m down to wiring now. I really don’t know what else to look at. Everything I’ve tested comes back within spec, hot or not.

I’m bald, but right now I want to grow hair just so I can pull it out
 
X7Kkndamt5ZGrYB39


Then again, I DO keep finding special gems like this.
 
Little things like that will burn you all right. (Bad pun.)

Took two days of hunting to find one of those which was the root cause of the fan blower motor no longer working in The Varmints' ZJ. In that situation it was a ground. We separated that wire out of the wiring loom, provided it with its own plug and added another ground wire to the chassis which was a shorter run.

You will need to figure out what that wire runs to and what needs to be done to drop the resistance.
 
Anak said:
Little things like that will burn you all right. (Bad pun.)

Took two days of hunting to find one of those which was the root cause of the fan blower motor no longer working in The Varmints' ZJ. In that situation it was a ground. We separated that wire out of the wiring loom, provided it with its own plug and added another ground wire to the chassis which was a shorter run.

You will need to figure out what that wire runs to and what needs to be done to drop the resistance.
Click to expand...

I've been afraid I'd have to open the loom, but it seems like the only logical next step here. Should be fun.
 
Worse, you need to follow that wire up the column or wherever else it goes on the opposite side of the picture.

Do you have schematics so you can identify its function?
 
I actually traced those two, they're clean as far as I can see. I think one of the original owners had an issue and corrected it. I reterminated that one and replaced the ig switch (again) and the issue still exists.

Need to check the integrity of the ground at the dipstick tube again. This has to be something dumb.

Zero codes tells me that the pcm is doing what it thinks it's supposed to do based on input, or lack thereof.
 
That I do not know.

But I would suggest that you may want to go beyond continuity and check for actual resistance. A poor connection may give continuity, adequate to start and run until warmed up. If you can find where you have higher resistance you may get a more useful clue about which connections deserve more attention.
 
Anak said:
That I do not know.

But I would suggest that you may want to go beyond continuity and check for actual resistance. A poor connection may give continuity, adequate to start and run until warmed up. If you can find where you have higher resistance you may get a more useful clue about which connections deserve more attention.
Click to expand...

Agreed, finding time and adequate bug spray for the task is the next hurdle. Mosquitoes down here need tail numbers.
 
FWIW, I would prefer mosquitos to snakes.

:wow:
 
Started in on the grounds. Found the stud in the block loose. Nut was tight but stud was loose, and wires are crispy. I’m going to just replace all the ground cables and connectors and see what happens next.
 
I do not know where it runs.

I just went and poked around a bit. It appears that it goes into the large bundle that runs between the PDC and the ECM, but I can't tell which direction it goes. I would have to perform harness surgery to a degree I really do not want to do.

The only possible clue I could find is a wire that looks fairly similar on the IAT plug. That one is black with a stripe which is close in color, but looks a little more red to my eyes. I don't know if the shade difference is real, or is just a consequence of darkening from age/exposure. If you are looking at FSM schematics you might try starting at the IAT and see where those two wires run.
 
Anak, good pics in that rewiring post.
I had a similar no-start in my previous 89
which turned out to be a loose nut at the
dipstick ground. Took me a very long time
to find...
 
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