Transmission stalling engine shortly after start up - Advice?

[Sczygelski14975]

I have a very unique issue. After starting my 1994 1078, as soon as the transmission appears to build some pressure it will stall the engine out.(in neutral) Repeatedly. I’ve checked all connections and I believe my controller is good yet. Voltage is 28-29VDC and 14 respectively. I know the next steps would be to drop the pan and potentially look at solenoids, etc. Looking for a little direction ahead of tearing into it all.

I’m very interested to see if anyone has came across this before or has heard of anything similar. Thank you in advance!

 

[NDT]

Very unusual. What brought you to the diagnosis of the transmission being at fault? Could the engine be dying on its own?
Transmission solenoids only apply pressure to clutches etc when power is supplied to them, so you can eliminate unintended clutch operation by unplugging the transmission connector.

 

[Sczygelski14975]

My diagnoses back to the transmission is due to the fact of how it acts. After starting the engine, roughly 15 seconds, the engine sounds slightly under load. It will progressively decrease idling rpm until the engine stalls completely. After restart, I have “throttled” into the “unknown load” and the engine spools up very nice and goes under obvious load to the point where it will stall again. I am very very confident that the engine is in good operating condition and is 100% not dying on its own. My thought is that I potentially have a solenoid stuck, which is causing some type of internal binding , or I have a torque converter issue of some type. When the engine is started and the load begins to ramp up, the driveline does not go under load visually. No binding or flexing of the truck. Confirming whatever is causing the load is between the engine, and transmission but not to the output. The only other item I have that I have not looked too deeply into is the PTO , as I have a hydraulic winch package

I’m a little stumped as I’ve never had an issue with this truck before, but we all know how that goes. It’s definitely one that doesn’t make entire sense To me just yet

I need to cycle the WTEC to see if I have any stored codes, that will be next.

I greatly value the opinion of others , in hopes of a quicker identification of the issue.

 

[GeneralDisorder]

Doesn't sound transmission related to me.

You say it runs for 15 seconds.... That's quite a while. Will it go into gear and will it move in that 15 seconds window?

Regardless - this smells like fuel system to me.

 

[Sczygelski14975]

After restart, the timeframe the engine can run will narrow as low as 5-6 seconds as the transmission still has some residual pressure built up. The truck will go into D and will move forward, however it will stall as the “unknown load” will pull the engine RPM down to 0. I understand that majority of the symptoms would appear to be a fuel system issue, but I can completely assure that the engine is strong and is not the cause of the “stall”. I am using the word stall loosely as that’s the best way I can currently describe it. After restart, I can command full RPM and it will spoon up and run like a BOH, build full boost, etc. Something within the trans/PTO is causing a very heavy load to the engine which it can’t overcome. I will try and attach a video link tomorrow to give some better visual / sound of what’s going on.

 

[Skyhawk13205]

I think each clutch should have a pressure switch, if they are pressurized you should have a code, can you check if you have any transmission codes.

a youtuber had a truck that the tranmission was seized and it ended up just getting really hot, another guy on Facebook had a tranmission that he seized and it just cracked the transfer case. I think the engine may be strong enough to blow up the tranmission if it is binding. Hope you find the issue soon, good luck.

 

[Ronmar]

Something would have to majorly fail for the engine to damage the transmission as all the parts are designed to deal with full engine output.

strange... could be something shorted in the wiring activating solenoids to select a gear ratio AND engaging the lockup clutch. I suspect this would save a code of some sort. Turn on ignition and press both arrows simultaneously to ender diag mode. The display will read D1(memory location 1), followed by 2 sets of numbers like 22 and 14, and will repeat the sequence. A mode indicator light indicates a current fault. Press the mode button to step thru the 5 memory locations and record the numbers and mode light status…

2 things you can try:
1. Chock the front wheels throughly, jack a rear wheel off the ground. Release the park brake and do not apply brakes unless you have to. If it is engaging a gear and lockup, if a wheel cannot spin it will brake the engine to a stop. If it continues to idle and spin a rear wheel well then it is somehow going into gear un commanded. It of course could also be engaging more than one gearset clutch combination, locking the trans internally and when the torque converter lockup pulls in, it brakes the engine to a stop.

2. Have you tried unplugging the transmission harness, or starting the truck with no transmission power applied? to remove all trans power, pull the cover on the VIM module under the pax dash and remove the pair of 10A fuses.

this will leave power to the rest of the truck, but you will not have a neutral start signal from the trans controller, so will have to crank the engine by jumping across the large terminals of the aux start relay down on the drivers frame rail to crank the engine. But with the run solenoid powered by the ignition switch, it should start when cranked…

if it is an electrical issue, the engine should start and idle Just fine with power removed…

this of course could also be a mechanical issue in the valve body allowing pressure to build in hydraulic circuits un commanded, or some blockage downstream on a return circuit causing pressure to backfeed into the hydraulic circuits causing issues. If this is the case, a no trans electrical test run will have the same symptoms…

 

[fuzzytoaster]

This is a very odd issue. Any transmission codes on the gear selector? This may be barbaric levels of bashing rocks together but.. drain the transmission system and start it. If the issue goes away then you've validated your transmission based issue. How does the fluid smell?

 

[GeneralDisorder]

Screams not a transmission problem. Lets see that video please.......