1993 4L80E Rapid 'Slam' shifting from 4 to 3rd and back to 4th - Help

[WarWagon]

As I go WOT or 3/4 or more throttle at a speed below 61 MPH where it can downshift to 3rd: I get a rapid gear hunting 3rd then 4th then 3rd again and shifting hard enough to hear/feel a slam. It will also hunt when going on an on ramp. Rapid is 3 gear changes in 5 seconds.

Manual shift to 3rd will hold it in that gear.

No codes. Will still allow OD and TCC lockup after it does this.

I know the front 2 prong sensor wires have the insulation falling off them and the rear sensor of the same plug is also in poor shape. I will be repairing these and want to make sure this covers the problem.

Any other things I need to check that would hunt gears with a steady throttle and speed or slight acceleration?

 

[ak diesel driver]

TPS glitch?

 

[WarWagon]

Checked it and only once watched the wiggle test fail, but, could not rule out the probes as it did not fail again. TPS .5v closed throttle over ~4v WOT. No spikes or drops in the range.

Any internal trans issues that could cause it to not hold a higher gear and fall back into a lower gear?

Code 83 from TPS mod.

 

[WarWagon]

Popped a code 22 today with hard shifting and no OD.

 

[THEFERMANATOR]

Popped a code 22 today with hard shifting and no OD.

That's a TPS code. Almost always when you have a hunting issue on a mechanical pump 6.5, it's a flat spot in the TPS.

 

[WarWagon]

Fixed it!

I re-adjusted the TPS for the code 22 and cleared it up. It was under 0.5v at idle. Still had the issue.

I forget who pointed out the 1993 computers being unreliable on here. So thanks to the forum for this tip. I had a spare 1993 computer sitting around so I swapped it in. Problem is gone.

Time will tell if this computer has the flash/flicker the SES light with no codes issue. Otherwise the wiring on the last 1993 was the cause of that weirdness.

 

[bk95td]

I had some of your symtoms on my 92. I finnally drove with the tech 1 hooked up and watched what was happening. The pcm was loosing the throttle signal. I replaced the pcm and all was good. All of my 92- 93s have had the pcms replaced.

 

[WarWagon]

And the problem comes back!

It is having issues with the 2-3 shift at times and the 1-2 shift in a parking lot. Shuttle shift maybe?

Compression braking with the TCC override switch locked is also causing a bad shimmy over 2500 RPM.

Trans shop hooked up a scanner and did a range on the TPS - Ok.

I suspect trailer towing and manual TCC override may have caused a mechanical issue in the trans like ruined the TCC clutch?