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My 4L80E trouble codes

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taskunitbruiser

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It was very tricky (the bolts were very difficult to access) but got a new TPS installed today!!

With the TPS sensor wire unplugged it has been shifting fairly well but still runs high RPMS in the upper gears. 60mph is about the practical limit now and I'm running 3200rpm there. 800rpm at idle so I dont think the tach is just faulty, plus traffic is passing me when I am maxed out and I otherwise know the speedometer is accurate. My guess is that without the TPS connected the torque converter is not locking up. What else could make high RPMs in 3rd and 4th gear with a newly rebuilt transmission and converter?

I thought once I go the new TPS in, the RPMs might drop and I feel the converter lock and prove me correct. Instead I get limp mode with the new TPS. Either the TPS needs adjustment (I installed it in the position I took the old one off) or the TCM just won't talk to the TPS anymore.

Any ideas? What is a differential diagnosis of RPMs being way to high when cruising, particularly with a rebuilt trans?
 
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taskunitbruiser

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I will recheck for error codes. Going to call a guy Monday that I have heard had a scanner that fit an H1. Seems like a scanner for the transmission could allow manual shifting and help diagnosis a bad TCM.
 
Mogman

Mogman

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If you find a scanner it will not likely allow any manual control, that is a very early and basic TCM and the H1 was a civy truck so it would have a OBD connector you do not have.
For the most part just getting the codes and some other very basic stuff like RPM is all the diag on that TCM.
Why there is no market for a reader for the HMMWV, but of course if there was I am sure with all the newbies coming on board they would sell like hot cakes not knowing how limited the information would be.

You should not drive that truck any distance until you have no codes and it is acting correct.
Pull the codes.
 
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taskunitbruiser

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Mogman, do you think the torque converter not locking in 3rd and 4th gear would cause the high RPMs? I have no reason to believe the transfer case or differentials are bad. The engine power is not getting to the wheels as it should!
 
Retiredwarhorses

Retiredwarhorses

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taskunitbruiser said:
Mogman, do you think the torque converter not locking in 3rd and 4th gear would cause the high RPMs? I have no reason to believe the transfer case or differentials are bad. The engine power is not getting to the wheels as it should!
Click to expand...
yes, you Will get higher rpms if your TC is not locked up, your brake switch needs to be adjusted, I have a cheater cable I use to test my TC lockup, the 24v is always present on the connector, the switch opens and denies voltage to the TC solenoid, thus unlocking the TC when you come to stop.
 
Retiredwarhorses

Retiredwarhorses

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Mogman said:
If you find a scanner it will not likely allow any manual control, that is a very early and basic TCM and the H1 was a civy truck so it would have a OBD connector you do not have.
For the most part just getting the codes and some other very basic stuff like RPM is all the diag on that TCM.
Why there is no market for a reader for the HMMWV, but of course if there was I am sure with all the newbies coming on board they would sell like hot cakes not knowing how limited the information would be.

You should not drive that truck any distance until you have no codes and it is acting correct.
Pull the codes.
Click to expand...
the scanner plugs into the harness connector at the transmission, the scanner is plugged in parallel so your can take control or monitor what the TCM is doing.
 
Mogman

Mogman

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Retiredwarhorses said:
yes, you Will get higher rpms if your TC is not locked up, your brake switch needs to be adjusted, I have a cheater cable I use to test my TC lockup, the 24v is always present on the connector, the switch opens and denies voltage to the TC solenoid, thus unlocking the TC when you come to stop.
Click to expand...
That would still simply show up as a code 37 or 38 yes?
 
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taskunitbruiser

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Thanks for brake switch idea.

Can anyone explain why it shifts well (still high RPMs at high speeds) with the TPS sensor wire unplugged and then goes into limp mode when I plug it back in? With a new TPS and no codes? Got 5V ref on sensor wire and continuity to ground after cleaning it.

My original thought, once I had the wire ok, was the TPS is bad and sending a low throttle position and/or just garbage input to the TCM; no data [unplugged] was better than wrong data. This explained why it worked so much better with it unplugged. Now I am just more confused.

I am thinking the direct connect transmission scanner to include/exclude the TCM and/or a brake switch are next logical steps.
 
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taskunitbruiser

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Retiredwarhorses said:
yes, you Will get higher rpms if your TC is not locked up, your brake switch needs to be adjusted, I have a cheater cable I use to test my TC lockup, the 24v is always present on the connector, the switch opens and denies voltage to the TC solenoid, thus unlocking the TC when you come to stop.
Click to expand...
Can I just unplug these two wires? One is for TC lock signal and one for the brake lights?
 

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taskunitbruiser

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I think the brake lights will just stay on if I did this. Can anyone confirm if one side is lights and one for the torque converter? If I knew which I could just unplug the TC side and it would help it lock in 3rd and 4th gear? I may be way off here.
 
Mogman

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taskunitbruiser said:
I think the brake lights will just stay on if I did this. Can anyone confirm if one side is lights and one for the torque converter? If I knew which I could just unplug the TC side and it would help it lock in 3rd and 4th gear? I may be way off here.
Click to expand...
All the information you are requesting including a description of how the switch works is in the troubleshooting guide.
Try page 73
Operating without the TC lockup is not advised as the torque converter creates much more heat.

Also you cannot simply short the wires to simulate a no brake condition as it will detect a stuck switch, you would need to connect a switch in place of the TCC brake switch and open the switch when you brake and close the switch when you accelerate.

And yes there are two switches, a TCC brake switch and a brake light switch.

Look at page 75 for the procedure to test using a DVOM.
 
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taskunitbruiser

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I called the guy that rebuilt the transmission. He agreed the torque converter must not be locking. He said the converter lock is good for about an 800 rpm drop. I asked if he had a scanner that plugged into the transmission directly and he said he did not have one, but they had one at the shop he worked at 20 years ago.

Still need to figure out why limp mode with TPS plugged in and with it disconnected converter won't lock. Frustrating. Mogman is saying I can't just unplug the brakes will need to run a switch. Want to test this next.
 
Mogman

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If you read the suggested page in the troubleshooting manual you will realize unplugging the wire will only tell the transmission the brakes are on all the time.
If you are going into limp mode with the TPS plugged in you must start there anyway, the transmission will NEVER work correctly without the TPS and if plugging it in puts the transmission in limp mode then you have a problem with the TPS, or the TPS circuit,,,you need to start there and do some troubleshooting rather than just plugging and unplugging stuff.
Have you read the codes with the TPS plugged in and after confirming it is in limp mode?
Have you checked the signal voltage coming from the TPS?
Do not worry about the brake switch until you figure out why the transmission goes into limp mode with the TPS connected...
 
Mogman

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Here is the TPS circuit, you simply take a volt meter and pierce the insulation on wire 355 with the positive lead of your meter and ground the negative lead, you should see aprox .5v at idle and 4.5V at WOT (wide open throttle) Run switch on and of course you want to unplug the glow plug temp sensor.
Troubleshooting the TPS is fairly easy.
As you will see if the voltage at wire 355 is below .2v at idle of 4.9v at WOT you will set a code and go into limp mode.
I suspect you will see less than .2v at idle.
TPS.JPG
 
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