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Yes thats true i believed i have ruled out bad PCM and EPROM chip since both have been changed and issue persists. Unless BPAA is the wrong one however i know BPAA has been in the truck a long time, even during its good running days, so i dont think thats any issue. as for the grounds, i have...

here are some videos of what is happening while driving, if that helps: Pressure drop during shift: https://www.youtube.com/shorts/H4lbePGYaeY PCS command info during a similar type of slow drive: https://www.youtube.com/shorts/DmCK5LuxE54 PCS command info at a standstill and with some brake...

Ok back with another update. I got a completely different ECM and EPROM chip (complete unit) from a different vehicle, with the BPAA chip so this time it was compatible. However this did not cure it. The shifts may be a little different now but fundamentally the pressure drop is still there. I...

Its interesting that with everything going on over there our friend took such an interest in a 4L80E with line pressure dropping out unexpectedly. Although i cant say his comments really aided the discussion.

I'll do whatever it takes at this point. Money im not too worried about just wanna get this thing back on the road and working sooner than later. Thanks for checking that online. If you are referring to putting the trans in limp mode by unplugging it so that it defaults to full pressure, i have...

I'm assuming the reference current and feedback current channels in GMTD scan is telling you amps going to the line pressure solenoid and amps coming back, so basically desired(commanded) vs measured I would think...but I'm no expert. I can get my hands on an PCM for a 94 blazer w/ 6.5 diesel...

Thanks. So what's that telling me? Temperature on the left axis -40 to 80 Celsius and the top axis is pedal position %?? Or am I reading it backwards? Regardless line is pretty steady at 130 or so if that's in PSI so much much higher than I'm seeing

Yup I'm thinking it's for a manual trans, I should have done my homework. So I am not sure if my PROM chip could be causing the line pressure drop out and I need to try a different one....or if something else is going on still. Obviously not the ECM itself causing the problem, unfortunately...

Old ECM 16212488 , BPAA, 86BPAAM252690210. Chip says BPAA 16216871 New one: ECM 16212488 , 862488W252860754. Chip says 1621 BNTL 5282

so today i got an ECM in with the exact same PN. I plugged in that ECM and tried it and the trans goes immediately into limp mode upon startup, however no codes, so i will run the scan program and see if i can find any issues. However so far i dont notice anything being off. I swapped the PROM...

well i ran a manual ground anyway and it had no effect. I took a lead and went from the existing ground location on the engine to the existing ground pin in the PCM. It did not have any effect.

Try this: https://youtube.com/shorts/H4lbePGYaeY?feature=share

Right, that makes sense to me, but i cant imagine that 1amp would be commanded in the middle of a shift, thats basically idle pressure at around 1800 or 2k rpms which is right around peak torque for this engine, and in 2nd gear, under throttle, the pressure rise is completely different than 1st...

Both, so far as i know. If i remember correctly there are two channels, reference current and feedback current to PCS. These channels match very well, as i monitored both. I did not notice any discrepancy between the two. Amperage during the 1-2 shift is around 1.04amps. Before and after the...

With the help from dbrannon I was able to get a scan program attached to the truck today. And verified just about everything was right where I would have expected it, except for PCS current during a shift. Anyone have any ideas of what checks I should do with this thing connected to the laptop ...

no scanner, its OBD1 so i am pulling codes with the paperclip and flash-count method. there was a ground strap attached to one of the bell housing studs, i recently removed that to see if it made any difference with what was going on, no change. I did check the wires on the trans housing to make...

Wow thank you dbrannon, that wiring diagram helps a ton! So upon further investigation, it appears my line pressure solenoid may be commanding a low pressure once the vehicle shifts into 2nd, even though throttle is steady or increasing. Not sure why this is, but almost appears its a vehicle...

that was my first thought as well, however i cant find any cracks or any concerning areas in the valve body passages or any of the case passages! and i've looked through them extremely closely. Also checked 2nd accum bore and seals for possible leaks. Went back through the valve body to make...

Ok so i have rebuilt this Godforsaken trans and changed out all the clutches, seals, gaskets, etc again! Got a new RECON converter. I did do the dual feed mod to the direct clutch while i was at it....... by removing the center support sealing ring and direct clutch seal, and plugged the hole in...

Yeah, you are right. I think i was incorrect in my diagnosis. I drove a year with a great working trans however without a locking torque converter, so i removed the torque converter to replace it with a rebuilt one because i figured the internal piston broke or something on the original. When i...