Suspect ECM and/or TPS but no codes

Searched for hours on this and now can't find my notes, but I suspect I have two issues going on right now. Can anyone offer confirmation or other ideas? No codes are being thrown, so I can only go based on observed symptoms.

1. Once in a while (maybe every six months?) the truck will start (restart after being driven and fully warm) and immediately die. It might take several tries to start again at that point and will idle roughly for a short period. If I give it a little gas, that helps. Feels like starting a carbed vehicle with a bad choke while cold.

1a. I don't seem to have a high idle, even when starting in cold weather. Engine fires right away and typically runs smoothly, but it's at normal idle level as if it was already warmed up.

I suspect ECM. Any way to further diagnose? Could it possibly be related to a bad TPS? (see below)

2. Torque converter locks up nomally, but it won't unlock unlock until I slow down to about 35 to 37 MPH, regardless of load. I can stomp on the skinny pedal to force a downshift, and that will work, but until then it's lugging really bad even to the point of torque converter (?) rattle. This really sucks when towing a car trailer! I have already adjusted the TV cable per a video I found online.

2a. Under moderate to heavy acceleration at about 45-50 MPH, just after shifting to 3rd, trans will downshift to 2nd, then back to third in a couple of seconds.

I suspect TPS. I've read some troubleshooting info. on this, but I'm still unclear if I can test using standard multimeter on my TPS. Will the probes push in from the outside of the TPS wire connector while attached, or is there a better way to do this? Sounds like it needs to be tested on the vehicle. If I find dead spots in the voltage and want to replace the TPS, which companies make a good one? I see Mopar-labeled ones for around $75, then all sorts of other brands like Wells, Walker, Delphi, Autex, Airtex, Standard Motor Products, etc. for anywhere from the $40 range down to the $20 range. Obviously, Mopar is the most expensive. Are others good, or should I buck up on this one?

Thanks in advance for any help and/or recommendations!

I've had a few beers and am feeling "gamey," so I'll have a go...

1. Once in a while (maybe every six months?) the truck will start (restart after being driven and fully warm) and immediately die. It might take several tries to start again at that point and will idle roughly for a short period. If I give it a little gas, that helps. Feels like starting a carbed vehicle with a bad choke while cold.

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My first thinking is a dying crank position sensor. I had similar issues when mine reached the end of the line. Could also be a leaky fuel injector.

1a. I don't seem to have a high idle, even when starting in cold weather. Engine fires right away and typically runs smoothly, but it's at normal idle level as if it was already warmed up.

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Mine does the same. I don't think that these engines use a "high idle" when cold that steps down to a warm "low idle" as they warm up. I'm thinking that this is normal for our engines.

2. Torque converter locks up nomally, but it won't unlock unlock until I slow down to about 35 to 37 MPH, regardless of load.

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Prior to my tune, my tranny would behave exactly the same. Factory programming seems to really try and lock the converter as soon as it can which in my opinion is a kind of stupid way to try and increase economy. Under part-throttle acceleration, this REALLY kills acceleration.

I can stomp on the skinny pedal to force a downshift, and that will work, but until then it's lugging really bad even to the point of torque converter (?) rattle. This really sucks when towing a car trailer! I have already adjusted the TV cable per a video I found online.

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That "rattle" sounds like spark knock to me. Does your engine use oil?

2a. Under moderate to heavy acceleration at about 45-50 MPH, just after shifting to 3rd, trans will downshift to 2nd, then back to third in a couple of seconds.

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Gear hunting perhaps? Sounds like the engine's torque is inadequate for the computer's planned upshifts forcing it to downshift. This would totally coincide with your engine's spark knock (assuming that it exists). Worst case scenario, could be loss of compression.

Honestly, I have no idea how to "test" a crank position sensor. When mine was going kapoot, I initially thought that the ignition coil was going, but ohm testing confirmed that it was not the problem. I ended up being "pretty sure" that the CPS was the problem and ended up being right.

If you are losing oil, it is almost always a blown intake plenum gasket on these engines. This issue can cause a myriad of problems including spark knock, loss of power and misfires. And yes, I had a long battle with all of those prior to doing the repair.

I doubt its a bad PCM. TPS sensors going bad are fairly common on these trucks so that's a possibility, if its high miles and never been changed it wouldn't be a bad idea just to change it. I would only use the Mopar one.
Your torque converter sounds normal to me, have you had the truck awhile? has it changed or always been that way?
The main reason the PCM likes to keep it locked is the trans runs much cooler with the converter locked. If its an issue towing use the OD off button and shift it manually.

Thanks for the brainstorming!

Not sure how to describe the lugging vibration/rattle, but it's not spark knock/detonation. That's a separate issue I have that may point to the plenum gasket. It does require 91 octane or it will knock, but I'm not losing oil or coolant. Bought it from the original owner, and I don't believe he ever replaced the plenum gasket, so it may be failing.

For all I know, the noise/vibration could be the exhaust vibrating, but the fact that anything vibrates shows there's a problem, IMHO. If I'm down to 37 MPH or so in 3rd, and something is vibrating due to lugging when I'm at 1,100 to 1,200 RPM going up a hill, that torque converter should be unlocked to allow higher RPM. I really have to stomp on it to force a downshift or do it manually, which I do. Speaking of the word manual, this is one of the many reasons why I wish I had a stick shift!

I already just keep the OD off button selected in anything other than 55+ MPH driving, but that doesn't control torque converter lockup. It still locks and remains locked down to a point where the engine is lugging even when OD off is selected.

It used to have a fast idle when started, if I recall. Now it doesn't.

If you are really having to step on the pedal to get it to down shift i would suspect that your TV cable needs to be adjusted.

My truck had sloppy shifts that I felt were too early, didnt downshift easily, and upshifted too soon. I pulled the TV cable out aprox 1/8" and the thing drives a hell of a lot better.

Im sure rhe cables on these trucks are stretched and need a little adjustment now.

Max78 said:

If you are really having to step on the pedal to get it to down shift i would suspect that your TV cable needs to be adjusted.

My truck had sloppy shifts that I felt were too early, didnt downshift easily, and upshifted too soon. I pulled the TV cable out aprox 1/8" and the thing drives a hell of a lot better.

Im sure rhe cables on these trucks are stretched and need a little adjustment now.

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I agree, 1100-1200 rpm is pretty low, I can see why it would be lugging the engine.

When you say pull the cable out, are you referring to lining up slightly behind the connection on the throttle body, so less throttle opening pulls the cable? I set mine up directly in line, as in this video. https://www.youtube.com/watch?v=FdJ2LSemTXI

I assume if I line up a little bit back toward cab, it would take up any potential slack/stretch/slop & simulate more throttle opening. Is that the intent?

Blue Truck said:

When you say pull the cable out, are you referring to lining up slightly behind the connection on the throttle body, so less throttle opening pulls the cable? I set mine up directly in line, as in this video. https://www.youtube.com/watch?v=FdJ2LSemTXI

I assume if I line up a little bit back toward cab, it would take up any potential slack/stretch/slop & simulate more throttle opening. Is that the intent?

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I couldn't tell you a reference because a little goes a long ways.

I slid the cable housing towards the firewall 1/8" to get later, firmer shifts.

I have done this on a couple 46re transmission and I set the TV cable by test driving it, I don't rely on reference points because you never know how accurate they will be.

Set it back about 1/8" to 3/16" from being aligned when throttle body linkage is closed. No improvement. Should I go further, or as I suspect, is this likely not the problem?

Starting and dying plus lack of higher idle in cold weather screams iac to me. Probably gummy. When you start and it dies it's probably sticking and not opening forcing a kill. Also would explain why gas helps, iac is out of the equation at first sign of throttle input.

May try doing a fluid and filter change with band adjustment, run for a hundred miles or so, drain and refill. These tq converter may not be liking the fluid quality and consequently the pressures.