transmission issue troubleshooting

**uhlhazard** · 09-20-2014

Hello I started doing tuning just a few weeks back. I'm realizing the learning curve especially with my 94 4.3 cpi engine/code and sticking with the stock chip just datalogging for now.

Anyways yesterday I noticed some odd transmission behavior. Light throttle in 3rd at 25-30mph the trans jumps back into 2. Seems like if you give it a little fuel it shifts gears really quickly. I went around the block and made the attached xdl. Anyone familiar with this issue? I checked the trans fluid and it was at the top of the cold mark @ 190* fluid temp. I have a deep sump pan/filter from a late model 4l60e so I'm doubting this is due to a low fluid condition despite it being slightly low.

I recently had a code 42 "Ignition Error" blink the service engine soon light on and off so I'm hoping I can blame the distributor and be on my way. Can anyone make heads or tails of my datalog?

This is all on a 1994 GMC T15 Jimmy with a 4.3 Vortec/4l60e

**uhlhazard** · 09-20-2014

I noticed the speedometer on playback was really jumpy so I went out and swapped out the drac with one I have on-hand. Seems the problem has disappeared.

I did a 2nd datalog and tried my best to get a repeat of the trans issues. I replayed that recording and got similar speedometer jumping around. I just recently replaced my VSS in the tcase with another from the JY. I certainly hope these failures are not connected!

**buddrow** · 09-20-2014

Glad to hear you fixed it. Those pesky DRAC modules will get you every time lol.

Buddrow

**uhlhazard** · 09-20-2014

Thanks Buddrow. My first time dealing with a DRAC I thought it was a transmission computer until a few weeks ago reading a lot of amazing info on these boards.

Will confirm on a longer trip tomorrow and post results incase someone is having a similar issue googling down the road.

**uhlhazard** · 09-22-2014

Took a 2 mile trip north and found the issue still persists. Going to swap out my vss with wifey's and see if I'm killing them or if I have a wiring problem. If I put the trans in 2 via shifter I get zero shifting craziness so I believe that isolates the hydraulic system and points towards electrical.

**buddrow** · 09-22-2014

Always check the wiring/connecter at the sensor. On GM espesically, it is common for the insulation to degrade and allow the vss wires to contact each other and cancel out the signal.

Buddrow