Need help with 4l80e not shifting right.

[X-cabsquarebody]

I put an 8.1 / 4L80E in my 91 craw cab. I cut down the factory harness. Engine runs great, Trans is not shifting right. The Trans its out of an 2002 ton truck. I put a filter in it before I installed it. The Trans holds 1st gear till the motor is turning about 5 grand, and you have to lift off the throttle to get it to shift in to 2ND. 2ND is the same as 1st. And when you let off the throttle when its going down the road, the Trans goes out of gear, no engine braking at all, touch the throttle, it engages instantly. With to wheels in the air, the scan tool shows the computer shifting the Trans, and no codes for Trans.
Any input would be great! Thanks.

 

[philjafo]

If it was a 350 or a 400 I would say it sounds like the vacuum modulator, but the 4l80e is controlled electronically. So assuming the motor, trans, pcm, and wiring harness all came from the same donor truck I would be checking the wiring, maybe vss signal or a vacuum sensor. You would think a problem like this would give some kind of error code in the pcm. Do you have a code reader that can give live data for example maybe the vss is giving incorrect speed signal due to different gearing or tire size.

 

[X-cabsquarebody]

I hope to go this evening and drive it with the scanner hooked up to it. That way we can see what's going on when its under load.

Good idea about gear ratio, I'll check that too.

 

[X-cabsquarebody]

Truck is back at the house. Got tired of sitting around with my finger in my ass. I'm gong to try another wire harness. If that does not fix it, then it had to be something internal in the Trans. I do now have a back up plan, just running out of time to get it usable.

 

[HotRodPC]

And you're positive the trans was working good before you installed it? No issues with it in the previous vehicle. I would be leaning toward wiring and ECM issues too myself.

Have you had it working correctly at all in new swap vehicle??? Pretty much trying to get at, it's a known good trans, and we're starting from scratch on the install correct?

 

[oneluckypops]

Sounds like a pretty cool swap, Few questions for ya though. You say you cut down a factory harness for the swap? Absolutly nothing wrong with using the factory harness BUT, what computer are you using?

Others have already stated Gear ratio changes. Which is for good reason, the transmission has to have a CORRECT VSS signal for it to shift properly.

I presume with it being a 91 you are already using an electronic speedometer? How did you wire the VSS to the speedometer? The Correct way to do so would be to wire the VSS to the PCM, then the PCM to the Speedometer. If your VSS is connected directly to the speedometer with out being ran thru the PCM the signal is incorrect pulses and will prevent the Transmission from shifting correctly. Part of the PCM's job is to convert the VSS signal. So make sure that is all correct.

I could give you LOTS of Variables for the Transmission not shifting correctly but rather then doing that lets get some facts of the swap to figure this thing out.

What PCM are you using?
Who Reprogrammed the PCM?
What Tire size are you running?
What gear ratio are you running?

 

[X-cabsquarebody]

I'm running an 12200411 computer, the correct one for an 8.1 / 4L80E combo. Its flashed for a 3500 G-van, with the correct tire size and gear. That its what the shop was double checking. My truck its an 91 and I do have an electric Speedo, but I'm leaving my Speedo separate from the computer.

Now I did unplug the out put speed sensor, and presto,,,,,, its shifting. But, I know there its some thing wrong. Thanks for you thoughts,,,, can I get a few more please?

 

[oneluckypops]

I'm running an 12200411 computer, the correct one for an 8.1 / 4L80E combo. Its flashed for a 3500 G-van, with the correct tire size and gear. That its what the shop was double checking. My truck its an 91 and I do have an electric Speedo, but I'm leaving my Speedo separate from the computer.

Now I did unplug the out put speed sensor, and presto,,,,,, its shifting. But, I know there its some thing wrong. Thanks for you thoughts,,,, can I get a few more please?

please explain how your leaving your speedo seperate from the computer? Not sure I understand how your set up

 

[oneluckypops]

I'm running an 12200411 computer, the correct one for an 8.1 / 4L80E combo. Its flashed for a 3500 G-van, with the correct tire size and gear. That its what the shop was double checking. My truck its an 91 and I do have an electric Speedo, but I'm leaving my Speedo separate from the computer.

Now I did unplug the out put speed sensor, and presto,,,,,, its shifting. But, I know there its some thing wrong. Thanks for you thoughts,,,, can I get a few more please?

Ok if you unplugged the OSS and the transmission is shifting is is VERY possable that is your problem. Unplugging the OSS makes the computer substitute values via the ISS and continues to command the shifts.

More then likely if you drive it with the OSS plugged in with a scan tool plugged in you will see the computer is not commanding the shifts.

I am usually not one fore throwing parts at problems but in yourcase it may very well be worth the 30 bucks for an OSS (VSS)

 

[X-cabsquarebody]

I have 2 4L80E trans. I swapped out the OSS,,,,, no change. Tomorrow, I'm going to pull sensor, and see of the reluctor wheel is in there. The trans had the input speed sensor only when I got it, a plug was in the rear out put hole. I'm starting to think there is nothing of the sensor to sense. Does this make sense????

The speedometer has its own speed sensor in the transfer case. The AC signal from the sensor goes the the DRAC module, were it is calibrated, and converted to DC . Then it goes to the speedometer. My truck had a 4L80E in it when I got it. The wiring for the trans left with the TBI harness. The original trans had 2 speed sensors for the trans, and one in the t-case for the speedometer.

 

[oneluckypops]

I have 2 4L80E trans. I swapped out the OSS,,,,, no change. Tomorrow, I'm going to pull sensor, and see of the reluctor wheel is in there. The trans had the input speed sensor only when I got it, a plug was in the rear out put hole. I'm starting to think there is nothing of the sensor to sense. Does this make sense????

The speedometer has its own speed sensor in the transfer case. The AC signal from the sensor goes the the DRAC module, were it is calibrated, and converted to DC . Then it goes to the speedometer. My truck had a 4L80E in it when I got it. The wiring for the trans left with the TBI harness. The original trans had 2 speed sensors for the trans, and one in the t-case for the speedometer.

Yes it makes perfect sense. Typically a 4x4 truck equipped with a 4L80E will have a plug in the OSS hole, the VSS in the tailshaft of the transfercase is what is used for the second sensor.
If the Transmission was a 4X4 transmission it more then likely does NOT have a reluctor wheel inside the Transmission for the OSS because they use the transfercase VSS.

If I am interpreting this correctly you are trying to use both sensors in the transmission for the PCM, and then a 3rd sensor for your DRAC Module.

A simple fix would be to disconnect the VSS from the Transfercase, Then connect the wiring from the OSS on the Transmission to the Transfercases VSS. This will make your transmission shift correctly, but will have your speedometer disabled. Simple fix though, you do NOT need your drac Module. Instead you need to connect your speedometer to your PCM, so long as your PCM has benn programmed for your current gear ratio and tire size your speedometer will still be correct.

If you can provide me with the specs from which the wiring harness was used I can tell you which terminals you need to use.

 

[X-cabsquarebody]

It's an 2002 engine and trans. Harness has a blue and red PCM connectors. Computer is an 12200411.

The speedometer has 2 wires going into it, if you know which 2 wires to connect to the Speedo, that would be awesome. Going to look and see if the trans has a reluctor wheel on the out put shaft today.

 

[oneluckypops]

It's an 2002 engine and trans. Harness has a blue and red PCM connectors. Computer is an 12200411.

The speedometer has 2 wires going into it, if you know which 2 wires to connect to the Speedo, that would be awesome. Going to look and see if the trans has a reluctor wheel on the out put shaft today.

Ok I will look at the diagrams and let you know which wires you need to hook up.

The problem with using 2 sensors on the transmission and then a third 1 in the transfercase is when you are locked in 4 low the computer will not recognize it because it is getting its readings before the transfercase, that is why 4x4 trucks have a plug in the rear speed sensor on the transmission and then utilize the VSS in the transfercase. Does that make sense to you?

 

[X-cabsquarebody]

It's working great now! There was no reluctor in the trans. Hooked the wires to the Speedo sensor and presto! It shifts! Big t thanks to oneLuckypops for getting my brain to think, and for the feed back.

Now I just have to figure out the wires for the speedometer. I know you have the alldata, I have pinouts for the computer, just don't know how to hook it up, which wire goes to which . Thanks again.

 

[oneluckypops]

I am trying to post a diagram of the instrument cluster but can not figure out how to upload a Pdf file, it says its to large.