4l80e not locking up

[Meece93]

Vehicle in question is a 1999 GMC K2500 5.7L 4l80e 4x4



My question is what all electronics wise would prevent the ecu from commanding lockup? The torque converter would lock up prior to me pulling the engine for a GMPP 395 cam swap. I can command lockup with my scan tool and it locks up perfectly fine. I've went back and replaced all part that were changed during the cam swap with Delphi/Genuine GM/AC Delco Gold parts. I've traced all ground wires and ensured they were in good shape and installed where they were before. All codes that were present have been fixed and rechecked multiple times. Only part I'm left waiting for is the Delphi distributor to replace the el cheapo I installed during the swap. To add to the confusion I let the truck sit for 2 weeks while on vacation and the first time driving it I had lockup for about 3 miles then gone again. Anyone have any advice on where to go next? Thanks in advance.

 

[Supercharged111]

Log for misfires, that will prevent a lockup.

 

[Meece93]

Log for misfires, that will prevent a lockup.

Just logged them and getting 100+ misfire counts on cylinders 1 & 6.

 

[Meece93]

Log for misfires, that will prevent a lockup.

Just for giggles I did another crank relearn since I didn't notice anything on the plug and everything but the icm and coil is brand new. Now my misfires have moved to cylinders 3 and 4. Bad crank sensor? Not getting any codes at all.

 

[Supercharged111]

I'm guessing this is the stock blackbox PCM? Counts on 3&4 just as high as 1&6, i.e. 100+? Such counts are enough to prevent a lockup. When's the last time you did plugs and wires? Is the cap and rotor new in whatever distributor you have? There's no need to unload the parts cannon, but a fresh tuneup is in order if it's been a while. Can you ohm out the plug wires?

 

[Meece93]

I'm guessing this is the stock blackbox PCM? Counts on 3&4 just as high as 1&6, i.e. 100+? Such counts are enough to prevent a lockup. When's the last time you did plugs and wires? Is the cap and rotor new in whatever distributor you have? There's no need to unload the parts cannon, but a fresh tuneup is in order if it's been a while. Can you ohm out the plug wires?

Yes stock black box ecm. Counts are just as high. Forgot to mention the counts were driving down the road. Plugs and wires were done 6 months ago with acdelco oe plugs and united motor products packard wires. Brand new Delphi distributor just installed today with united blue streak brass cap and rotor. The parts cannon has already been fired at this thing lol.

 

[Supercharged111]

I know the blackbox isn't good at pinpointing which cylinder is misfiring, which is why it is not set to throw codes for individual cylinders. How's your fuel pressure? If you have the original poppet injectors, those are super sensitive to fuel pressure and will cause misfires if it's off. They also have a tendency to be junk after this much time which also causes misfires.

 

[Meece93]

I know the blackbox isn't good at pinpointing which cylinder is misfiring, which is why it is not set to throw codes for individual cylinders. How's your fuel pressure? If you have the original poppet injectors, those are super sensitive to fuel pressure and will cause misfires if it's off. They also have a tendency to be junk after this much time which also causes misfires.

Fuel pressure when checked a few months ago was 58-62 when cranking and around 58 when running, no leak off. Pump is about a year old. Upgraded to the mpfi when I got the truck about 1.5 years ago.

 

[Schurkey]

Perhaps a moderator will move this thread from "The Garage" to "Transmissions".

 

[Meece93]

I know the blackbox isn't good at pinpointing which cylinder is misfiring, which is why it is not set to throw codes for individual cylinders. How's your fuel pressure? If you have the original poppet injectors, those are super sensitive to fuel pressure and will cause misfires if it's off. They also have a tendency to be junk after this much time which also causes misfires.

Glory hallelujah. Turns out the old crank position sensor wasn't spaced out correctly and got whacked. New sensor installed with shim and lock up has returned. Misfires got no higher than 10 during the whole trip. Thank you for pointing out the misfire possibility as I would've never suspected it.

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