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I need a li'l help with a 4L80

bison

bison

Well-Known Member
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Location
Near Peace River-Alberta
I aint experienced with these AT's,
need some diagnostic opinions.

Buddy's truck.
92 GMC 6.5 td 2 w dr 4L80 AT,250 k on it. all original

truck runs and shifts fine when first started cold,after it warms up and driven for a 1/2 hr or so all is OK. shut it down and start and drive it again it wont go past 2 sec gear, will shift hard in sec.Reverse allways works
No problem when stone cold.

filter and fluid changed by dealer twice.

The ADL connector is inoperative at this time,so i dont know if a DTC was set.
No SES light either.

wadda ye think
 
Had similar problem. Was VSS but you need to check for codes. why would the AdL connector be inoperative ??? You have a 92 though, not sure if it even has one. I guess it must.
 
Acesneights1 said:
Had similar problem. Was VSS but you need to check for codes. why would the AdL connector be inoperative ??? You have a 92 though, not sure if it even has one. I guess it must.
Click to expand...
Gawd,i start hating all these acronims. There's to many.
What is VSS stand for?

there's a ADL conn,damn thing is dead though.I'll have to fix that first i guess.:rolleyes5:
 
The shift solenoids and there are some other little seals in there that can and do cause issues with no shift or ???? issues.

I had this issue with my DaHoooley and we dropped the pan, replaced the solenoids and a few seals.

There is a service bulletin out on this issue.

The thing is this, the seals around those solenoids are going south and when cold the oil is thick enough that the seal will hold the pressure needed to make things work and when hot they leak too much.


If you are not confident, take it to a tranny shop that you trust. Mine was less than $100 to fix including fresh oil and filter.

MGW
 
thanks for piping in Missy.

I aint scared to rip any thing apart,i'm well versed in wrenching on most anything that prowles the earth,i just need some pointers.

The dealer was the one not able to fix the problem,they suggested a new tranny to the owner. A $3000 repair for a $500 truck

I think I'm gonna get a All Data subsciption for this vehicle,only 16 bucks or so.
That,and the suggestions of all on board will lead me to succes I hope:thumbsup:
 
On a 92 many things can cause it to go into limp mode(2nd only). First thing to check for that vintage is the trans harness, if it has one with a bolt in the center of the plug then replace the internal trans harness and the plug on the vehicle side. Many of these have already been done though as this is a VERY weak area of the 91-93's and caused ALOT of havoc. You also need to check for codes as that truck does have an PCM per say in it to control the glow plugs and transmission. Also that truck if 4X4 has 3 different speed sensors in it whereas 94+ only used 2. With 250K miles though there is a good chance she's getting some wear inside and fluid leakage is getting you when she warms up. Start with the basics and go from there though.
 
My '93 did the same thing when i first got it, (both the '92 & '93 mechanical IP and computer only runs the auto tranny). I replaced the shift solinoids, and the wiring harness internal & external, and tcc solinoid plus filter & fluid while i was there. After that mine was 100% ok, until about 1 1/2 years later when it pushed out the front pump bushing from previous crap lodged in the small passages. Think i spend a total of about $150 on all the above, and i'm firmly convinced that if that was done by the PO instead of him just driving it until i wouldn't shift every day i would have been fine just replacing those components.
Don
 
I'll have a go at it on all above suggestions.
it'll be a while before i can dig in this truck,to many other things on the go now that are more important.

i'll post back with the findings,
thanks.
 
The first thing I would do is get a scan tool hooked up to it to see what is happening with all the sensors. Throwing a wiring harness and solonoids at it may not be the problem. The throttle position sensor plays a large roll in the operation of the tranny. Engine rpm sensor,input speed sensor output speed sensor,and trans temp sensor are the other sensors used that can cause problems. Diagnose before throwing parts at it.
 
bk95td said:
The first thing I would do is get a scan tool hooked up to it to see what is happening with all the sensors. Throwing a wiring harness and solonoids at it may not be the problem. The throttle position sensor plays a large roll in the operation of the tranny. Engine rpm sensor,input speed sensor output speed sensor,and trans temp sensor are the other sensors used that can cause problems. Diagnose before throwing parts at it.
Click to expand...
no kidding,what scan tool would work on a 92 ?. I got GMTDScan, but that is for 94/95,doubt if it works on a 92 though
 
The ADL connector is inoperative at this time,so i dont know if a DTC was set.
No SES light either.

wadda ye think
Click to expand...

Maybe, repair your DTC communication problem first........It might save you some time/money/aggravation in the long run?
 
bison said:
no kidding,what scan tool would work on a 92 ?. I got GMTDScan, but that is for 94/95,doubt if it works on a 92 though
Click to expand...

My old snap-on brick 2500 works fine, just no bidirectional control(cant manually shift it, control lockup or line pressure). My Tech-II does it all, but not needed really for this TCM, too many $'s for what it will do.

When the trans acts up is it going into limp 2nd, or do you still have 1st/2nd? When it shifts to second does it shift late/high rpm or at a normal rpm/just hard?

There is no CTS on this truck.

Engine speed sensor bad/unplugged/bad wire should default you to limp/2nd only.

Unplug the TPS, take it for a drive, should still shift, low throttle shifts will be late/high throttle shifts will be early if every thing else with the trans/TCM is working properly.

Fix your ALDL problem and check engine light, these will flash codes just like your other older GM's. So far I think its a TPS/wiring problem.
 
midniteplowboyy said:
My old snap-on brick 2500 works fine, just no bidirectional control(cant manually shift it, control lockup or line pressure). My Tech-II does it all, but not needed really for this TCM, too many $'s for what it will do.

When the trans acts up is it going into limp 2nd, or do you still have 1st/2nd? When it shifts to second does it shift late/high rpm or at a normal rpm/just hard?

There is no CTS on this truck.

Engine speed sensor bad/unplugged/bad wire should default you to limp/2nd only.

Unplug the TPS, take it for a drive, should still shift, low throttle shifts will be late/high throttle shifts will be early if every thing else with the trans/TCM is working properly.

Fix your ALDL problem and check engine light, these will flash codes just like your other older GM's. So far I think its a TPS/wiring problem.
Click to expand...
I got no Snap on scanner,just GMTDScan and AE. So,reading the codes will have to do on this one.
 
After it shifts to second when it acting up, does it still have 1st when you stop or is it stuck in 2nd until you shut the truck off?
 
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