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

**uhlhazard** · 09-22-2014

I got on my back in the dirt yesterday and gave it a visual inspection. It doesn't have any obvious issues and I always make sure my wires are inside good loom. If the next series of tests fails I'll be testing the wiring via my fluke. Will report findings here asap.

Theres only 1 thing I hate more than finding a bad wire in a harness, and thats PLUMBING!

Thanks for the help!

**buddrow** · 09-22-2014

You can check the incoming signal to the drac as ac volts and the output at the drac, a scope is good here but an analog meter may work as well to check for pulses out. If the readings are solid, check the drac out at the pcm. If you can log data you should be able to see the actual loss of signal.

Buddrow

**uhlhazard** · 09-24-2014

I tested without my autoprom connected which made no change whatseover. I then tested a second time with my cruise module unplugged and the same issues persist.

Next will be to swap with wifes vss. If that works I gotta figure out if I'm destroying vss or if cooincidently 2 of them have weirded out.

**uhlhazard** · 10-01-2014

So I didn't borrow the wifes because she has the only running vehicle on the ranch right now. Talking to my brother and he has a np241 in one of his project trucks. I go SWEET, I NEED A VSS. Tossed it in and the trucks running and shifting awesome. No drama. Attached is a log of a test drive with everything spot-on.

Thanks for yoru help Buddrow. What are the odds I'd have 2 bad vss? Will post longterm conclusion later. All this np241 research got me wanting to convert to an np243 because I like my electronic shifting. The 6 pinion planetary and the wider chain is pretty sweet too!

**uhlhazard** · 10-06-2014

Thread shift. Np233 to np243 upgrade would be a pretty simple swap with my 1" body lift. The fundamental limiting factor is my vacuum controlled front diff actuator. The np24x uses an electronic switch in every application I've seen therefore not worth the trouble converting the front diff to electronic actuation.

Further research concludes that my np233 is probably an np233HD evidently up to 1994 and possibly 95.5 the np233 got the 1.25" wide chain and 4-6 pinion planetary. compared to the normal 1" wide chain with 3 pinion planetary. Good times indeed!

**kevinvinv** · 10-07-2014

I have a question on transmission issues in general. Do the 4L60's post trouble codes that aren't readily seen when you scan out the engine codes? I also am wondering what the "trans" tuner pro RT files are for? Is there a different datastream or something that comes from the trans? noob.

Thanks.

**buddrow** · 10-07-2014

Kevin,

The trans codes generally will not set the check engine light but should, in OBD1 pcms, display trouble codes along with the engine codes.

The transmission parameters in the xdf are used to "tune" different aspects of trans operation just as the engine parameters do for the engine.

Buddrow

**kevinvinv** · 10-07-2014

My scanner tells me I have an "ODM Failure" from the trans. Cant seem to find out what this is. This is a 94 Chevy. I thought I'd try to hook up TunerPro with the trans xdf to see if it provided any more info... thoughts?