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4L80E No Power - Recent Engine Swap

cander27

cander27

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Came over from the HummerNetworkForums (HML) at the suggestion of Will L. due to the Transmission Legend (THEFERMANATOR) that patrols the halls of TTS.

I have a 1995 H1 Hummer 6.5 NA, recently cracked the old block and put in a 6.5 GEP with a Super 77 turbo so now I have a mechanical turbo.

First off, I had a transmission light on but it turned off after I put in a new speed sensor (Tcase). I have also replaced the TPS hoping that was the problem. Eventually pulled the speed sensor fuse in an attempt to get the truck to the default "get home" settings, but that didn't change anything.

I've had the truck home for two weeks now and been driving it after the engine swap. I recently re-timed it, shorted out the 40amp Maxi fuse during the timing, replaced the fuse and was back on the road. There haven't been any issues with the transmission, no hard shifts, no power issues, nada. The only oddity is starting from a stop, occasionally the truck would act like the brake was still applied after taking my foot off the brake, as if half the power was applied, and then it would allow all the power to go into the drive train. That is the only symptom I had prior to what is now happening.


Day of the problem:
Driving to work without issue, parked and headed to the Forestry HQ for a shoot. No issues after parking and stopping at the first location, but hit a funky bump in the parking lot that shifted the truck (noting this in case it is related) to the point I saw the shifter move. Parked and turned off the truck at the Forestry HQ, found out my crew was in a different area so started the truck back up and drove over.

Problem starts
Going up a hill I begin to notice the truck starts losing power, but the engine RPMs aren't going down. I stop at the top of the hill to find my crew while still in OD, then put my foot on the accelerator and the truck acts like it is in Neutral.

- Engine RPMs go up, engine revs, but no power on the drivetrain. I try Reverse, Drive, 2nd and 1st with the same effect.

- Turn off the truck and begin smelling for fluids, looking for leaks, checking transmission levels without finding anything unusual.

- I get back in the truck, start it and shift into Reverse and can feel the truck go into gear and then I can back up. As soon as I shift to Drive the truck again, acts like it is in Neutral.

- I put the truck in Park, turn it off. Turn it back on and shift into Drive, and I can move forward but the truck seems sluggish. I park it in a spot and had to run up the hill to go to work.

A few hours later...

- Come back to the truck, start it put it in Reverse and the truck moves. I shift to drive and the truck shifts into drive. I push on the accelerator and get some power, but it soon acts like it is in Neutral again.

-When the truck begins acting like it is in neutral, in any gear (R, N, OD, D, 2, 1) I can rev the engine and see the RPMs go up. It just can't apply the power to the drivetrain.

- Going under the truck I had a co-worker shift through the gears. The driveshaft would barely move, and sometimes not even move. Typically when I shift my truck there's a nice sounding *chunk* and the feeling the truck just shifted. Now when I shift, you can barely notice if it shifted into gear.

- Today after replacing the Speed Sensor and TPS I tried an experiment. I sat with my foot on the accelerator a 1/4 depressed while in OD, the engine would run at a higher RPM and then start applying power causing the RPMs to drop and the truck to move forward for about 2 seconds and then the RPMs would go back up, the engine would gain power audibly again and no longer move the truck. I kept my foot on the accelerator and the truck did this about 6 times. It was very gradually going in and out of applying power to the drive train...though not enough power at any point in time to push itself over a curb. It does the same thing in reverse. It seems extremely weak.

Summary of the Problem
Engine has power but can't apply it to the drivetrain.


Went out today to have the Forestry Mechanic use his personal scanner, but he had to run before he could scan the truck.

BUT, had a new discovery. The Glow Plug Relay appears to be dead or faulty. No Wait light or clicking of the relay. I can start the truck after a long cranking. This glow plug relay was replaced after we put the new engine in as the old one that I swapped from my old 6.5 NA had the same issue. No wait light, no clicking, no start. This makes me highly suspicious there is something electrical going on.

I have checked all the fuses, each one. Made sure they weren't blown and seated properly. No issues.

I was worried it was the shift linkage at first as the decision was made at the shop my truck didn't need the extensions. After this happened I put them on yesterday just in case making sure everything was lining up, no issues (other than still no power at the drive train).

If it is the torque converter there was zero warning aside from the slow pull-away from dead stops occasionally. Never had any jerking, halting, unusual shifts or power problems with the old engine or new engine in the last two weeks.

The transmission fluid might be slightly on the full side, but I don't know if it could cause this. I did wonder if the truck had the cooling lines reversed and will check that when I go out to the truck again tomorrow, but that is only speculation.

I've spoken with a number of the H1 Hummer specific mechanics and they each think it is something different.

I'm out of ideas, I've put $20k into fixing a cracked block only to have the truck stuck. Any ideas or help would be well beyond appreciated!
 
My 1st check would be to check the fluid level with the engine off, then start it up, and recheck the fluid level. See how much the level drops when it starts. Your symptoms sound alot like a cracked filter seal which makes it suck air instead of fluid. And to eliminate electrical, unplug the round plug at the trans on the drivers side and the trans will go into limp mode leaving you with reverse and 2nd gear.
 
THEFERMANATOR said:
My 1st check would be to check the fluid level with the engine off, then start it up, and recheck the fluid level. See how much the level drops when it starts. Your symptoms sound alot like a cracked filter seal which makes it suck air instead of fluid. And to eliminate electrical, unplug the round plug at the trans on the drivers side and the trans will go into limp mode leaving you with reverse and 2nd gear.
Click to expand...

That's fascinating information I hadn't come across, thank you! Actually, the trans level is reading little high.

Then the next step would be to unplug the trans harness and see if it can go into R and 2nd which rules out other electrical issues?

What would cause a cracked filter seal? I guess that is the next step IF the above shows it is not electrical - draining the trans pan and checking the filter?
 
cander27 said:
That's fascinating information I hadn't come across, thank you! Actually, the trans level is reading little high.

Then the next step would be to unplug the trans harness and see if it can go into R and 2nd which rules out other electrical issues?

What would cause a cracked filter seal? I guess that is the next step IF the above shows it is not electrical - draining the trans pan and checking the filter?
Click to expand...
Dont hurt to change filter and freshen up the fluid a little.
Nice thing about the 4L80E is they do have a drain plug. Located a little high but it gets out the most of it. Just be a little careful when dropping the pan, whats left in there will have the ability to slosh on out. 😝😳😹😹😹
 
THEFERMANATOR said:
My 1st check would be to check the fluid level with the engine off, then start it up, and recheck the fluid level. See how much the level drops when it starts. Your symptoms sound alot like a cracked filter seal which makes it suck air instead of fluid. And to eliminate electrical, unplug the round plug at the trans on the drivers side and the trans will go into limp mode leaving you with reverse and 2nd gear.
Click to expand...

checked fluid cold, then running. The level dropped a little bit below the fill line but came back up after about 10 minutes of running.

Unplugged the harness from the transmission and the truck still acted the same as before. In Reverse and in 2nd. Eventually it grabbed onto reverse after revving it a bit, but then went back out after some backing up. Never engaged 2nd.

I’m guessing this narrows it down to the transmission? What do you suggest I check next? Pull the pan and inspect the filter for damage?
Appreciate the help, just being able to narrow it down to the transmission is a breath of fresh air in solving the problem.
 
cander27 said:
checked fluid cold, then running. The level dropped a little bit below the fill line but came back up after about 10 minutes of running.

Unplugged the harness from the transmission and the truck still acted the same as before. In Reverse and in 2nd. Eventually it grabbed onto reverse after revving it a bit, but then went back out after some backing up. Never engaged 2nd.

I’m guessing this narrows it down to the transmission? What do you suggest I check next? Pull the pan and inspect the filter for damage?
Appreciate the help, just being able to narrow it down to the transmission is a breath of fresh air in solving the problem.
Click to expand...
Yup, most likely drop the pan and filter, inspect that filter seal.
Sometimes a PO, if, they change the filter will leave the old seal in place. Sometimes when the seal gets changed, the bore the seal is pounded i to gets scars from reckless seal removal procedures, if when You get the seal removed, You find gouges in the bores surface. Use some No 1 Permatex sealer and give the bore a nice coating. That should fill in and seal any gouges. At least that has worked for Me.
 
To remove the old seal, I use a smaller Snap On screw driver, use a plastic hammer to pound on the plastic screw driver handle, place the blade of the screw driver so it will wedge between the trans and the flange of the seal, tap the screw driver handle until it wedges its way in, move the blade over a little repeat, work around it some, then after getting the seals flange wedged away from the housing, use a little more force until it begins to cave in the seal body, it then should pry right on out without damaging the bore.
 
This may sound extremely stupid...but by seal are y'all referring to a seal of some sort that goes in the hole on bottom of tranny? Where the nipple on top of the filter snaps into? I've had tranny fluid changed 3 times since owning the truck, and never saw the guys that did it for me change any seal..they just yanked the old filter out and banged new one in...
 
Stoney said:
This may sound extremely stupid...but by seal are y'all referring to a seal of some sort that goes in the hole on bottom of tranny? Where the nipple on top of the filter snaps into? I've had tranny fluid changed 3 times since owning the truck, and never saw the guys that did it for me change any seal..they just yanked the old filter out and banged new one in...
Click to expand...
Yup, there is a seal in that bore. If it has never been changed then, good chance it could possibly he sucking air around the seal.
If You buy a transmission filter, open the box, most likely there will be a new seal within the box.
 
Crap, just typed more instructions and they just disappeared.
the parts stores has a big square funnel device that sets atop of a drain pan. About 3 foot square and made so juice runs to the center and into a depression and flows out into a drain pan.
Those are mighty helpful when changing transmission fluid.
Also, it seemed I had to turn the pan crosswise to the vehicle to get it to come free of the cross mount and cross over exhaust pipe.
 
cander27 said:
This guy! https://www.hummerpartsguy.com/FILTER-TRANSMISSION-4L80E_p_1696.html
Click to expand...
I see the filter element is the same color as other elements I have seen.
The picture does not show that it has the seal included. It also says for all models but also says for models without drain plug.
If Your trans pan does not have a drain plug, it would be worth getting a drain plug kit from the parts store and installing one. Just be sure it is in an area away from the filter and linkages. I have installed DP kits in quite a few transmission pans and it sure does making changing filters much easier, a lot less mess too.
 
Early 4l80e's had a silicone seal that was prone to cracking. Later they came out with a metal sleeve with an integrated rubber lip seal that was much tougher. The fluid level should drop a good 2-3 inches with the engine running. When the filter seal fails they have a hard time picking up fluid when it is below the top of the hot zone.
 
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