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Discussion Starter · #1 ·
Hi guys, glad to finally join. Been reading for years. I really hope mark kovalski chimes in, he knows his stuff.
I am mechanically inclined.

I have a 96 powerstroke that I plan on flipping for a profit. The transmission bogs the engine down in first and reverse ONLY WHEN HOT. Acts normal when cool. Fluid is at proper level. Looks and smells good. I decided to start examining the transmission harness after reading about e4od electrical gremlins on this site. Harness seems to be in good shape after a brief inspection. Connector on the solenoid pack was a little dirty so cleaned it and put di-electric grease on it. Plugged it back in, and no change. I then unplugged the harness, and the transmission did the same thing. Bogs the engine down to ~500rpm in 1 and R. Sometimes it seems like it will let go and idle in gear like normal.
The transmission did not lockup in 3 and od like it is supposed to either. I have not scanned for codes yet, but there are no idiot lights on. I am new to diagnosing computer controlled engines and transmissions, but I have somewhat educated myself on the terminology. I don't think that it is toast because the fluid looks great and the issues are consistent.
I'm glad to recieve any correction and advice that will help me resolve this problem. Thanks guys,

Andy Durrett
 

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I think the problem is that the torque converter clutch is drifting on. The cause of that is low transmission pressure.

Low pressure is caused by low trans fluid, a miss installed internal filter, worn seals, or a worn pump.

The way to check this is to get a 0-350 PSI gauge with a 1/8" NPT thread. Install it in the test port on the driver's side of the trans. It is located towards the front, just above the pan. Record the pressure in each position at idle - PRND21.
 

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Discussion Starter · #3 ·
I think the problem is that the torque converter clutch is drifting on. The cause of that is low transmission pressure.

Low pressure is caused by low trans fluid, a miss installed internal filter, worn seals, or a worn pump.

The way to check this is to get a 0-350 PSI gauge with a 1/8" NPT thread. Install it in the test port on the driver's side of the trans. It is located towards the front, just above the pan. Record the pressure in each position at idle - PRND21.
Thanks for the reply. I will get a gauge on it tomorrow. Previous owner said it started acting crazy and that a simple fluid and filter change fixed it. I wouldn't be surprised if he put a cheap filter on it and it has fallen off over time. Out of curiosity, how would low pressure cause the TCC to engage?
Thanks In advance.
 

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That is way, way too high.

Check for codes. I think you either have a bad EPC (Electronic Pressure Control) solenoid or a bad wire to the solenoid.
 

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The EPC solenoid controls the line pressure regulator valve, so it controls the line pressure in the transmission.
 

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My guess is that you have a wiring harness problem that is causing all of those codes. The P1748 code is the one causing the trans problems.
 

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Solenoid pack on the way.
Replacing the solenoid will not fix the wiring fault. You need to inspect the harness for physical damage, and test each wire electrically with a meter to find out if it's broken or shorted.
 

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Which problem? Codes that are set when the wiring is not properly connected are irrelevant. Of course the circuit has a fault when you unplug it - it's not connected to the solenoid at that point. If you mean the transmission not shifting right when it's unplugged...
 

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Discussion Starter · #18 ·
Read the original post. The torque converter clutch engages with the truck in reverse and 1st positions. It does the same thing with the harness unplugged. Line pressure is also way too high both plugged and unplugged.
 

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With the solenoids unplugged you'll have max line pressure. With the shift handle in OD you will only have fourth gear with the torque converter unlocked. If you move the shifter to 2 or 1 you will have second gear. Reverse also works.
 
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