Hey guys I have a 1995 GMC Jimmy with 4.3 and 4L60 trans- 4 dr 2wd. A few days ago it started something new. If I'm going down the road while the trans is locked up in OD if I let up off the gas just a little bit and am giving it really light throttle it will unlock and then lock back up; it used to just unlock when I let off the gas completely. It's not just around 40 mph when it goes into lockup- it's at any speed that it's in lock up. If going straight down a road @ 55mph and I go down a slight hill and give it a little less gas it will unlock then go back into lock up when I hit the gas. I'm going to check the TPS sensor today when somebody gets here to hit the gas pedal so I can check the voltage. Any other thoughts/ideas? Thanks.

 

If it happens through a wide range of speeds, it could indicate that the Torque Converter Clutch itself is giving up. You could try replacing the TCC solenoid first though.

 

Uh oh that's not good! I've noticed it happening mostly around 45-55mph- but I haven't driven it much over 60. I checked the TPS voltage and it's within the proper range. When I bought the truck the guy had the trans rebuilt in it about 12,000 miles ago. Do they generally replace all those parts when they rebuild them or just test them to see if they work then put them back in? I wanted to try and get it to stop going in and out of lock up before it did burn up the clutch!

 

Does the TPS voltage increase smoothly from 0.5V at closed throttle to ~4.5V at wide open throttle? Are there any blips in the voltage as you move the throttle?

 

It was reading about .78v @ idle and I think 4.68 @ WOT. It seemed to be increasing smoothly. BTW the truck does have the OBD 1.5 . No CEL or anything though. As long as you are giving it just enough throttle it will go into lock up and stay there- if you let off just a little too much it unlocks then goes back in. Accelerating in lock up is fine- it stays locked in unless you hit the throttle hard enough. Thanks for the replies.

 

That doesn't sound right... The TC should unlock somewhere before you floor it... Even quick jabs at the throttle, no where near wide open should cause the torque converter to unlock. Almost sounds like you may be having an issue with line pressure in the trans...

 

I apologize for not being able to describe it well. It drives completely normal except for it seems to unlock the TCC prematurely. It does seem to unlock properly when given enough throttle. A jab will cause it to unlock. It's only with very light throttle- maybe pushing the gas 1/8 or less of an inch- that it will unlock and then lock back in repeatedly. If stepping on the gas a little bit harder- not hard enough to make it downshift or unlock- it stays locked up like it should. It used to just unlock when you let off the gas entirely- then lock back up when light throttle was reapplied. Everything else is completely normal- goes through the gears well, etc. Thanks.

 

You could still be having line pressure problems in the trans or possibly a worn TCC solenoid bore, but as suggested earlier in this thread, I would look into the TCC solenoid first. If that doesn't work, then you likely are looking at a new TC.

 

Thanks. I'll give the solenoid a shot first and hope for the best. The problem with it is that it's intermittent. I drove it the other night and it was fine the whole time. I've been keeping track of it for the past few days and noticed it mostly does it between 42-58 mph. It also does it more when the AC is turned off. Maybe because the AC puts more of a load on the engine? I also ran it wide open through the gears to make sure everything else was still shifting properly and it was fine.

 

Well I replaced the Advance Auto Parts TPS sensor a few days ago with a Delphi sensor and so far the problem has not occured again. Hopefully it'll stay working properly