Lock-up Converter Tech Question.

[AMCguy]

I have a 2008 GMC W3500. It has a 6 liter gas engine with a 4 speed auto.

In the city in either D3 or D4 the converter will not unlock when I roll onto the throttle a little. Even the slightest incline will pull the motor down. I can push harder on the pedal but get no unlock, then I get an undesired downshift. I don't want the downshift I just want the 3 or 4 hundred rpm the converter unlocking would give me.

It has good power up around 2,200 rpm but as soon as the converter locks up it drops down to about 1,800 rpm and falls on it's face.

Is there a way to manually switch the lock up? Like a do it yourself Tow / Haul mode.

Thanks in advance

 

[ods dan]

usually yes, you can put in a switch to lock or unlock.. not sure on that particular one.. but search online for the trans wiring and you should find it.

 

[nehog]

You may be able to get what you want with one of those software 'tuning' kits. (The ones that either plug into the ODBII port, or replace the ROM.)

Does this truck have an electronic throttle or a mechanical one? If mechanical, there will be a TPS and the adjustment on that affects lockup. Electronic throttles are different, and won't help you.)

 

[AMCguy]

The throttle is electronic. The transmission is a 4L80E.

I'm not looking for full manual control of the lockup and unlock, I just want to toggle between fully automatic lockup and me being able to prevent lockup.

It would be nice if it didn't unlock when I take my foot off the pedal. It would help with engine braking. But that is more complicated. I really just hate it locking up at low engine speed.

 

[Zeke]

I just touch the brake.

 

[bgott]

Isn't that transmission equipped with Tow/Haul?

 

[ddawg16]

I just touch the brake.

And the quickest way to verify that it's working properly.

You should see the RPM's jump a little when you touch the brakes.

If that works right....then the converter and related items are ok...

Has it always been this way?

 

[AMCguy]

The converter unlocks as soon as I lift my foot off the gas. (I wish it wouldn't) I think all GMs do this now. When I reapply the gas the converter will flash about 400 rpm but then locks right back up again. I then lose that 400 rpm.

This is all normal operation. I just don't like it.

It does not have a Tow / Haul mode. That's what I would like to create.