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4l80e Transmission Problem


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#1 cbholt

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Posted 09 September 2009 - 09:23 PM

I have a 93 GMC 2500 2wd with 4L80E transmission. Running down the road in third gear or overdrive, between 2200 and 2400 RPM's, the torque converter locks and un-locks constantly. Doesn't matter if your accelerating or coasting. It will unlock for about a second and then lock back up. and then about 3 seconds later do it again. The computer does NOT throw any codes. Nobody locally seems to be able to figure this out. The Transmission has been rebuilt 5000 miles ago and the Torque Converter Clutch was replaced twice. The assumption I am making is that it is the Torque converter unlocking, and not the transmission slipping. When it unlocks, the rpm's jump about 300 rpms. But it is possible im wrong. Any help would be appreciated.

#2 oldschool327

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Posted 09 September 2009 - 10:32 PM

Ok, you have a few things to check first before assuming the tranny is the problem.

The 4L80E gets information from various sensors to set clutch lockup and shift points. The two main items are the TPS and its adjustment, and the Crank angle sensor. These tell your TCM What position your throttle is at and how fast the engine is spinning. I just verified again in the Hydromatic book. This is where you should start. The TPS has a very narrow range of voltage adjustment that it needs to fall in and can only be measured with a go/no go throttle block and multimeter (or a fancy GM machine). Not even the Super Shifter or Tech II can do this. Then make sure the pins on the Crank sensor have the proper voltage and ohms.

After those are verified you could take out the input and output speed sensors from the driver side of the tranny and clean them with electrical or brake cleaner. There is a small magnetic nipple that build up metal flakes and rust over time. They have to be spotless for a good reading. Also has the Force Shift Motor been looked at?

This could be all kinds of item but those are the most suspect. Even your brake switch is wired into the TCM. Start with the above and if you still have problems I will upload the 4L80E manual for you to go through. It is big so it will take a bit.

I have been working on that tranny (my favorite) for 12 years now and it is very rare to burn one out after 5000 miles. Dont think I have ever seen an 80 go that early, so That is why i believe it is electrical, more on the motor side than the tranny.

Brian
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#3 cbholt

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Posted 12 September 2009 - 01:07 PM

I replaced the Throttle Postition sensor about 2 weeks ago. Is there anywhere online I can find the procedure for its adjustment? Also, where is the Crank Angle Sensor located on a 350?

#4 oldschool327

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Posted 12 September 2009 - 02:31 PM

This is a 5.7 gas motor, or 6.2/6.5?

Diesel are located just behind the crank pulley at a 15 degree angle to the drivers side. Gas should be in same spot.
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#5 oldschool327

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Posted 12 September 2009 - 02:54 PM

Here is a very good site for you 80 series owners that is public access. Goto the video section and it walks you through the TPS adjustment. Take a look at it all there is some good info on all the different switches and modules that effect the shift pattern of the 4L80. Hope this helps, let me know how it comes along.


http://www.transchoo...wnload_page.htm
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#6 cbholt

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Posted 14 September 2009 - 12:35 PM

I don't have any sensors behind the damper or around the timing cover. I have a suspicion that this is not the orginal motor, due to it has 265000 miles on it and runs too dang good. But it is a TBI 5.7 Is there anywhere else the Crank Sensor could be?

#7 oldschool327

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Posted 14 September 2009 - 07:24 PM

The CAS is located at 7 o'clock on the timing cover if you have one. If you do have one it should have 12V at the pink wire or Number one left pronge. If hooked at the yellow wire crank the engine you should have 5V. This sensor was added at around the 1995 mark so you might not have it.

Did you get a chance to adjust your TPS?
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#8 cbholt

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Posted 14 September 2009 - 10:20 PM

My motor must not have a crank sensor. I read in my chilton manual that they didn't start putting crank sensors on 5.7's till 96. I haven't adjusted the TPS yet. I have to find a guage block.

#9 oldschool327

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Posted 14 September 2009 - 10:41 PM

You do not need the block because you have the gas engine. The block is for the diesels. Below are instructions for the 5.7 TBI.

Put a voltmeter on the a&b terminals and adjust it with the key on to .54 volts. Oh and make sure you have 4 volts or more at wide open throttle.

There are three ports on the TPS...wire colors may vary from vehicle to vehicle...most are BLK, BLU, and GRY.
Switch the ignition power to ON, but don't actually start the truck. With a digital multimeter find the two wires that give a voltage reading of about 0.54VDC... Loosen the TPS just enough that it will move ever so slightly...this part takes a very steady hand. Adjust the TPS to a reading that matches the spec by +/- about .02VDC (that's what the specs are as far as I know) and tighten the TPS back down. Recheck the voltage and turn the ignition power off. Reconnect the TPS...go have a beer...done.
EDIT:
I wanted to give a little clarification on this since it is something I am actually confident in knowing how to do.
The BLK wire from the TPS is the GND. The other wires are the actual signal and reference wires. The reference wire (GRY) should read +5VDC. The DK BLU wire is the TPS Signal wire and it should be the one that varies with throttle position sensor movement.
Adjust the TPS signal with the key in ON but the engine NOT RUNNING. The idle voltage may be different for your particular application. I think yours will use the 0.54VDC spec +/-0.02VDC.
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#10 cbholt

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Posted 28 September 2009 - 08:33 PM

UPDATE:
I havne't fixed the problem yet, but I have made some progress and crossed a lot of things of the list of possible causes.
I have replaced the following parts:
TPS (and adjusted to .547 volts)
Both Speed Sensors.
Knock Sensor
Digital Ratio Adapter Controller (DRAC) has been calibrated to my exact Gear ratio and Tire size
Added a ground strap to Transmission.

On the upside, after all this work the truck is running and shifting better than ever, but the Torque Converter problem still exists.
When I added the ground strap it caused the torque converter to do its thing at slightly higher RPM. When I calibrated the DRAC, it caused it to only do it above 2500 RPM's, rather than between 2200-2500.

So what do I do next?

#11 R.A.O

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Posted 22 January 2010 - 08:27 PM

UPDATE:
I havne't fixed the problem yet, but I have made some progress and crossed a lot of things of the list of possible causes.
I have replaced the following parts:
TPS (and adjusted to .547 volts)
Both Speed Sensors.
Knock Sensor
Digital Ratio Adapter Controller (DRAC) has been calibrated to my exact Gear ratio and Tire size
Added a ground strap to Transmission.

On the upside, after all this work the truck is running and shifting better than ever, but the Torque Converter problem still exists.
When I added the ground strap it caused the torque converter to do its thing at slightly higher RPM. When I calibrated the DRAC, it caused it to only do it above 2500 RPM's, rather than between 2200-2500.

So what do I do next?



My 93 2500 had the exact same problem. I was told it was the torque converter, and you can tell that by pressing the brake when it jumps, that send a signal to the computer to disengage the torque converter. It may not be the torque converter, especially since you had yours re-built. There is a solenoid on the side of the transmission that may not be working, they have a tendency to wear out, that could be all it is, or simple as the wiring, the old wires sometimes can get loose or dirty and will send currents through the wires (im not sure which wires, but ones that run from the computer to tranny somewhere, not much help i know) as they touch or manage to make a connection if dirty. My truck is going into a good tranny shop this monday, i will post back here and tell you what the problem was on my truck, and hopefully that will help you out. Like i said what you are describing is EXACTLY what i am having. I have the 4L80E tranny on a 2500, but mine is a 4x4 with a 454 TBI in it.




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