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4L80E Replaced all Electronics and it Shifts Like Crap

btsayles

btsayles

Diesel Proficient
Messages
56
Reaction score
25
Location
Wisconsin Rapids
I'm getting so tired of this truck. All I do is work on the darn thing. I replaced all of the electronics in the trans and now it shifts into 2nd very hard. Not to mention that other gears also, but it is hardest into 2nd. I also installed a deep transmission pan and new filter. I originally replaced the electronics to get the torque converter to start locking back up again, but I don't think it fixed that either. I can't tell if the convertor is engaging or not. It's irrelevant either way if the trans blows up from hammering into gear. Another strange thing is that when shifting from 1st to 2nd with the lever, it takes it a second or two for it to shift and it shifts hard. When I put the lever in 3rd, it stays in either 1st or 2nd and won't shift into 3rd at all. THen when I shift it into D it will go through all of the gears. What is going on? It shifted lazily prior to replacing the electronics, but I would have driven it that way rather than dealing with this. This is starting to wear on me. It's going to snow soon and I need my plow truck.
 
Just hooked up gmtd scan and it confirmed what I thought. When I selected 1st it would shift up to 2nd. WHen I selected 3rd, gmtd said it shifted into 4th. But when I shifted into D, it shifted again. So I know that it couldn't have been in 4th. Is there just speed sensors that gmtd says that at that speed is in a respective gear? I am so confused. If I'm confused and have experienced this. I can only imagine what you guys are thinking trying to decifer this. HELP.
 
Did you just change out your differentials?

If so, you might need to modify your DRAC / VSS settings; your PCM takes input data from there, and uses it to play with your shifts, depending on your programming. Bad VSS Sensors will also screw up your shifting. They should give you a code, but don't always, or so I've heard.

Could also be a ground issue, but I'd check the input/output VSS sensors first.

Simon had a bad one a while ago...

http://www.thetruckstop.us/forum/showthread.php?17746-4L80-VSS

I found an article that might shed a little light on things:

http://idiventure.com/flashoffroad/Maintenance/SpeedSensor/SpeedSensor.htm

And the standard explanation of how to reprogram your VSS/DRAC:
http://www.tbichips.com/drac/
 
Another question. There is some type of sensor above where the selector lever and it's respective electronics are. There is another identical looking sensor located at the aft of the trans. What are these? The one on the rear of the trans has no plug connected to it and looks like there wasn't one plugged in there for some time. There is no lead around it that looks like it should be plugged into it. I'm guessing there should be something there. All the connections look good otherwise. Haven't messed with diffs yet. DTC 83 is set but has been since I thought the TCC wasn't engaging. I wish I knew what GMTD should look like to tell me whether or not the TCC is locking. It has been so long I can't remember what this truck used to do.
 
Speedo is working fine, but the cruise has been working intermittently. I guess I am partially inept. I need to put the vehicle on jack stands and run it while checking the voltage or resistance from the sensor on the transfer case? By the way, doesn't it seem strange that all of this would occurr after changing electronics in the transmission. Why would this vehicle speed sensor just pop up as a problem?
 
trans input speed sensor which is hooked up reads 1.517k and 1.458k for output which is not used. Swapped for its and grins.
 
Did you change out just the solenoids or did you change the force motor too? If you change out the force motor you may have to turn the torx screw on it ccw about 1/2 turn. When I had my trans rebuilt one time they turned it up some and it did the same thigh to the point that it chirped the tires goin into 2nd. Also, with your truck being 4wd, the front sensor you were talking about gets plugged in, the second one that you saw unplugged basically acts as a plug, then there is another one on the transfer case that should be plugged in. This is done so that the vssb can compensate for the truck being in 4lo.
 
Did you disconnect the batteries for 30 minutes to reset the adaptives? If not then most likely the adaptive memory for the trans shifts are off since they will be set to your old solonoids. And yes, the OBD1 6.5's DO have adaptive memory for the trans. Also there may be an updated PROM chip for your application that is to improve the 1-2 shift as this is a known problem in the early 4L80E's. Since you were having problems before the solonoid change though, the ECM may be sensing a trans problem and defaulting to max line pressure due to it.
 
Troubleshot all of the wiring to the trans from the pcm and found an enomily in the internal harness to the manifold pressure switch which was replaced. Had to drop pan again to see if it was pinched wires in the harness or the actual brand new switch. Two pins on the switch had continuity between eachother. AllData has troubleshooting procedures for everything but a ohm chart for the switch. I ohmed out the manifold switch that was replaced and there is no continuity between pins. I haven't been able to find a spec sheet on how to check the switch, but I have e-mailed the seller, electricaladvantage.net. Haven't heard anything yet, but they haven't done me wrong before. I expect them to let me know what the verdict is, and if I really did get a bad part. If anyone knows how the switch is supposed to ohm out, please let me know! I greatly appreciate the help from anyone. Thank you guys. Just disconnected batteries. When I hear something for how the switch is supposed to be, I'll see what the culprit is.
 
Does anyone have a mainfold pressure switch laying around that you can check the resistance between the pins. I can't find anything online or on AllData for a check for it. Thank you.
 
I've got one from a '95 that I rebuilt a couple years ago. I'll dig it out and check it if I can get a spare minute. I also have all the other electronics, because I was advised to replace everything, so if you need 'test parts' I can probably accomodate you.
 
Did not read every post, but we have had hard 2nd gear shifts for years. If I shut the truck off and restart it is fine until next time. Recently we put a OptiShift controller in a truck that was consistantly shifting hard into 2nd and it has since been shifting great. Do you have another PCM to try? maybe atleast that will tell you if the prob is the PCM. I have one out of a 95 truck for $50 if you want it.
 
Burning oil said:
Did not read every post, but we have had hard 2nd gear shifts for years. If I shut the truck off and restart it is fine until next time. Recently we put a OptiShift controller in a truck that was consistantly shifting hard into 2nd and it has since been shifting great. Do you have another PCM to try? maybe atleast that will tell you if the prob is the PCM. I have one out of a 95 truck for $50 if you want it.
Click to expand...
Truck shifted beautifully before doing electronics in the trans except for no torque converter lockup. I am putting it back together again today and I will let you guys know what is up. If I need a PCM I'll let ya know, but this one tested fine. It sounds like a good deal tho'. Thanks for the reply.
 
Found the little culprit. Wire broken but the coating was not about 1 foot from the trans pass through connector. Cleaned it up, soldered, and heat shrunk. SHifted into OD like a champ. Still shifts into 2nd really hard. How can I adjust that?
 
On the TCM trucks its a very common problem. On the PCM trucks not so much. I dont think you can ajust anything on the PCM.
 
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