4L80E Problems
06-28-2015, 04:39 PM
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4L80E Problems
I'm finishing up swapping a 2001 6.0/4L80e/t-case into my '95 Z71. Most of it seems to be working, but the transmission is giving me some trouble... I'm not real familiar with transmissions and the problem has been a bit of a moving target, so I'll give the rundown and hopefully some of the gurus here can point me in the right direction. Donor vehicle allegedly had ~100k on it, and I put a Transgo HD2 shift kit in it along with new filter and fluid during the swap. Harness was done by me with all connections soldered & sealed.
When I got the truck running, I drove it up for a state MVI (3mi away). Forward gears worked, but when I got there Reverse seemed to be locked up and the truck wouldn't back up. Fluid was a bit low, being the first time driving it, so we topped that off and I drove it home. Once there, Reverse worked just fine.
I put about 65mi on the truck, it shifted strong and all seemed good when the next problem showed up. It started to feel like something was bound in the transmission or driveline. As it got warm it seemed to start slipping (engine would rev without the truck accelerating) as though the clutches were the weak point between the engine and whatever was binding. It would roll freely in Neutral. The manual transfer case shifted through the gears fine. I put it on jack stands and found the driveshaft and rear axle/brakes moved freely. I also found a leaking wheel cylinder, so I replaced that and the brake shoes (and confirmed the e-brake was fully disengaged). The problem persisted so I pulled the trans pan and replaced the filter & fluid, but I didn't see any significant material in the pan or fluid.
I pulled codes and the only one I found was a p0300. While trying to chase that down, I ran the truck around the block and the forward gears significantly improved. So I drove it a little farther, but never got above 35-40mph. During this drive, 1st to 2nd gear shift was not near as firm as it used to be (not soft, but not ready to bark tires) and at certain loads there was a brief metal on metal 'whine' at about 20mph (I have a vid if it would help). I got the truck back home to find that Reverse was binding again. I have to stall it up to about 1000rpm to get it to roll backwards downhill. And when I let off the gas, it rocks a little like it's unloading something. Also, Neutral does not roll freely and if I give it enough throttle (~1500rpm) it will move forward in Neutral. Fluid appears full on the dip stick (if anything it may show a little high) but I don't think it took as much to fill after the 2nd filter swap as it had in there before... based on the dipstick marks, I may have had it 'overfilled' before.
Searches have turned up some good info, but nothing that quite matches this behavior. I hope it's a simple fix, but want to hear what the knowledgeable people think.
When I got the truck running, I drove it up for a state MVI (3mi away). Forward gears worked, but when I got there Reverse seemed to be locked up and the truck wouldn't back up. Fluid was a bit low, being the first time driving it, so we topped that off and I drove it home. Once there, Reverse worked just fine.
I put about 65mi on the truck, it shifted strong and all seemed good when the next problem showed up. It started to feel like something was bound in the transmission or driveline. As it got warm it seemed to start slipping (engine would rev without the truck accelerating) as though the clutches were the weak point between the engine and whatever was binding. It would roll freely in Neutral. The manual transfer case shifted through the gears fine. I put it on jack stands and found the driveshaft and rear axle/brakes moved freely. I also found a leaking wheel cylinder, so I replaced that and the brake shoes (and confirmed the e-brake was fully disengaged). The problem persisted so I pulled the trans pan and replaced the filter & fluid, but I didn't see any significant material in the pan or fluid.
I pulled codes and the only one I found was a p0300. While trying to chase that down, I ran the truck around the block and the forward gears significantly improved. So I drove it a little farther, but never got above 35-40mph. During this drive, 1st to 2nd gear shift was not near as firm as it used to be (not soft, but not ready to bark tires) and at certain loads there was a brief metal on metal 'whine' at about 20mph (I have a vid if it would help). I got the truck back home to find that Reverse was binding again. I have to stall it up to about 1000rpm to get it to roll backwards downhill. And when I let off the gas, it rocks a little like it's unloading something. Also, Neutral does not roll freely and if I give it enough throttle (~1500rpm) it will move forward in Neutral. Fluid appears full on the dip stick (if anything it may show a little high) but I don't think it took as much to fill after the 2nd filter swap as it had in there before... based on the dipstick marks, I may have had it 'overfilled' before.
Searches have turned up some good info, but nothing that quite matches this behavior. I hope it's a simple fix, but want to hear what the knowledgeable people think.
06-29-2015, 07:29 AM
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po 300 is random misfire, and misfire will make stuff act crazy and make you think theres something wrong with your trans.did you take off the intake? sure injectors ok? change fuel filter? double check wiring and grounds
07-01-2015, 01:32 PM
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Just the valve body mods.
I'd hoped it may be misfire related when it was the forward gears, but doubt it now. Diagnosing the misfire may deserve it's own post as I haven't had much luck there. Between the swap and trying to chase it down now:
Ignition-- new plugs & wires, spark tester shows all cylinders have spark. Plug gap was checked before install. Pulled plugs for inspection and all looked about the same.
Fuel-- new pump & filter; good pressure @ the rail & regulator tests good; confirmed injectors are wired correctly; noid lights confirm injectors are cycling; stethoscope sounds like all are cycling.
Engine was rebuilt during the swap with a small cam, so I don't think it's compression. EGR was eliminated. Haven't found a vacuum leak using smoke or propane. Rear O2s are functional and not tripping codes, so the cats should be ok. Tuning done by a reputable tuner. I confirmed FR O2s are wired correctly Bank 1-1, 2-2. Code is thrown in both open loop & closed loop, so I don't think the upstream O2s are bad. Running out of ideas...
I'd hoped it may be misfire related when it was the forward gears, but doubt it now. Diagnosing the misfire may deserve it's own post as I haven't had much luck there. Between the swap and trying to chase it down now:
Ignition-- new plugs & wires, spark tester shows all cylinders have spark. Plug gap was checked before install. Pulled plugs for inspection and all looked about the same.
Fuel-- new pump & filter; good pressure @ the rail & regulator tests good; confirmed injectors are wired correctly; noid lights confirm injectors are cycling; stethoscope sounds like all are cycling.
Engine was rebuilt during the swap with a small cam, so I don't think it's compression. EGR was eliminated. Haven't found a vacuum leak using smoke or propane. Rear O2s are functional and not tripping codes, so the cats should be ok. Tuning done by a reputable tuner. I confirmed FR O2s are wired correctly Bank 1-1, 2-2. Code is thrown in both open loop & closed loop, so I don't think the upstream O2s are bad. Running out of ideas...
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