4L80E 1993 6.2 no 1-2 shift

[Blue93cube]

New to the forum but have been reading a ton. 1993 G30 van, ex air force, 6.2/4L80E. Problems started with dead TCU, limp mode, CEL, was run this way for a while (off road only maintenance support vehicle). Replaced TCU, swapped chips. Now have 1st, no CEL, but no upshift. Not in od, d, or trying manual 1-2. Replaced and reset tps (before TCU) which had big dead gaps, both speed sensors, and 1-2 solenoid. Fluid looked good, light deposits in bottom of pan, nothing to note in filter. Recently, occasionally, under light throttle at mid rpm’s, 15-30 mph, on the level, it will seem to upshift then within a second or two, drop back down again, however, there is no engine braking when it drops under those circumstances. If a scan tool is the next stop, wondering if someone in the Pittsburgh area has one, or if there is a shop that can be trusted with the obd1 (incl diesel) stuff.

 

[NickTransmissions]

New to the forum but have been reading a ton. 1993 G30 van, ex air force, 6.2/4L80E. Problems started with dead TCU, limp mode, CEL, was run this way for a while (off road only maintenance support vehicle). Replaced TCU, swapped chips. Now have 1st, no CEL, but no upshift. Not in od, d, or trying manual 1-2. Replaced and reset tps (before TCU) which had big dead gaps, both speed sensors, and 1-2 solenoid. Fluid looked good, light deposits in bottom of pan, nothing to note in filter. Recently, occasionally, under light throttle at mid rpm’s, 15-30 mph, on the level, it will seem to upshift then within a second or two, drop back down again, however, there is no engine braking when it drops under those circumstances. If a scan tool is the next stop, wondering if someone in the Pittsburgh area has one, or if there is a shop that can be trusted with the obd1 (incl diesel) stuff.

Id put a bi-directional scan tool capable of displaying ODB1 trans data to see if the PCM is commanding an upshift out of first gear....If it is, then the problem is either electronic or valve body. If no shift is being commanded there's an incompatibility between your command and contorol (PCM) and transmission.

 

[Blue93cube]

Will a snap-on brick work or what other options are there aside from Tech2 for a 1993 diesel? Diy options seem to favor the 6.5td.

 

[NickTransmissions]

Will a snap-on brick work or what other options are there aside from Tech2 for a 1993 diesel? Diy options seem to favor the 6.5td.

Not sure, I dont have any time with the Brick but @Schurkey may know - think he owns or owned one.

And to be clear, are you hanging in first or does it feel like it's in neutral when upshifting during the instancrs it has made a shift from 1st to 2nd?

 

[Blue93cube]

This is all under light throttle as the 6.2 gets to uncomfortable sounding rpms quickly in first. Shifts into 2nd with no flare or hesitation, holds for a second, just long enough to think it might be ok, then feels like a downshift (revs go up quickly) but no engine braking when I let off the gas like I get rolling around in low. With no tach, I let it slow a bit before getting back into the gas and it’s definitely in first. I’m being extra cautious because I had a bad experience with an auto that decided first was good at 40mph due to bad vss..

 

[Blue93cube]

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[Blue93cube]

One thing that concerned me was the solenoids looked different from the replacements but I read that they have been updated over time.

 

[NickTransmissions]

This is all under light throttle as the 6.2 gets to uncomfortable sounding rpms quickly in first. Shifts into 2nd with no flare or hesitation, holds for a second, just long enough to think it might be ok, then feels like a downshift (revs go up quickly) but no engine braking when I let off the gas like I get rolling around in low. With no tach, I let it slow a bit before getting back into the gas and it’s definitely in first. I’m being extra cautious because I had a bad experience with an auto that decided first was good at 40mph due to bad vss..

Hmmm...wonder if your intermediate one way clutch (owc) is rolling over...those pre-97 units had the 16-element sprag clutch which was more failure-prone than the 97+ 34-element sprag...do you have 3rd or 4th at all?

 

[Schurkey]

I had an MTG2500 for ~20 years, (same software as MT2500) but never connected it to a Diesel. I expect it would work on the Diesel just fine, though.

 

[Erik the Awful]

1993 G30 van, ex air force

Bread van or van-van? If the walls could speak, you'd have a lifetime supply of dirty jokes and profanity. I imagine the interior is thoroughly trashed and held together with double-bubble. It probably reeks of Monster, gas station "tornados", and sweat.