Intermittent stalling

[alopeks]

Where do I begin??

'99 XJ, 4.0 (reman, installed 11/19) AW4, NP242, stock gears, 3" lift, 31s.
246K on the body/trans, about 37K on the motor.

Three times now, all a week or two apart, the engine has stalled within 30-90 seconds after seeming to start normally. First time, 4 weeks ago, was right after replacing the battery (new Optima red top) and resulted in replacing the alt, which failed a bench test but was warrantied by O'Reilly's. Second time (a week ago) it stalled in almost exactly the same place, just as I was leaving the alley. Was able to get it started only after several minutes of cranking, but once it chugged to life, it seemed to run fine after a minute. Today I was farther down the road, but not much. I also noticed that the temp gauge seemed not to work while it was cranking but not starting, but again after a few minutes it finally chugged to life, and then ran fine. So now I don't even know where to start looking...

Temp sending unit failing? Engine thinks it's too hot/too cold so changes the air/fuel ratio when it shouldn't? Old clogged cat that only restricts too much on occasion? Afaik, it's original...

I've been getting a CEL related to torque converter lock up solenoid (P0740) on and off for a while, but it doesn't seem to coincide with the stalling. Unless every now and then it locks up the TC at idle and stalls the engine??

I fear I have reached the limit of my skills... Help!

-alopeks

 

[Tim_MN]

Fix known defects. The cat converter is 100,000 miles past due, and likely O2 sensors are too. You cannot diagnose what is causing a specific problem if there are multiple malfunctions causing multiple problems.

Diagnostics: What diagnostics and trouble shooting have you performed ? Is or was the Check Engine Light ON ? Have you scanned for additional stored or pending trouble codes related to the symptoms ?

So diagnostics can be more efficient, start with : Is the stalling lack of fuel, or faulty engine sensors / faulty wiring / faulty PCM ?

 

[Saudade]

What are the symptoms of code P0740 ?

MIL (Malfunction Indicator Lamp [Check Engine & Service Engine Soon])lights on with stored historical P0745

TCC does engage/disengage

Disabled shifting function with engine stall when coming to a stop

Harsh shifting, transmission slippage, transmission overheating

Fuel efficiency concern

https://www.troublecodes.net/pcodes/p0740/

 

[alopeks]

The only code it's ever thrown is P0740, and the only symptom I've ever noticed from it is slightly higher rpm on the highway. I've never seen any other codes, and that one hasn't been present for the stalling issues.

I don't know if/when the cat has been replaced. Does that sound plausible as a root cause?

-alopeks

 

[Tim_MN]

Fix known defects. The cat converter is either 100,000 miles past due, or due again, and likely O2 sensors are too.

You cannot diagnose what is causing a specific problem if there are multiple malfunctions causing multiple problems.