Trans won't upshift at WOT

**MMLMM** · 06-27-2009, 06:29 PM

Just a note as I am seeing this often....

Problem:
trans holds gear and will not shift into next gear at wide open throttle unless you lift a little bit.

Whats happening is truck is not making the tq. where it needs to make the shift. The problem is it is not getting enough fuel to do so.

Fix:
Most often the fix is a new fuel filter as the filter is clogged and not letting enough fuel to engine.
Could also be due to a big tune and not having a lift pump, again not getting enough fuel.

**ob_1jr** · 06-27-2009, 06:47 PM

Good info..i will make this a sticky.. I have noticed the same questions/problems.

**MMLMM** · 06-27-2009, 07:07 PM

Quote:

Originally Posted by ob_1jr

Good info..i will make this a sticky.. I have noticed the same questions/problems.

meh, not sure it is sticky material, but I worded it good so it would come up in a search.

**Dmaxwrenchkit** · 06-29-2009, 12:25 PM

In addition to the above mentioned issues failure to upshift can also be a vacuum leak in the fuel supply up to the injection pump (air being sucked into the fuel supply at the Fuel Filter housing, engine rubber hoses, fuel pickup assembly in tank, cracked water sensor, loose fuel filter, loose water sensor etc.) All these may help reduce the headaches many are experiencing.

Thanks

Dale

thebeast02 · 07-22-2009, 05:51 PM

Im havin the same problem with my 02 LB7 its like it just dies at wide open throttle. i was wonderin if it could be the fuel injectors. the truck has about 117000 miles on it.

allisondan · 07-22-2009, 07:15 PM

All low power issues will cause this. As the guys stated in the thread Fuel etc. Lift you foot off the throttle and bingo it shifts. Its not getting to calibrated govern up shift speed there for it cant make the shift.(output speed)

jc1843 · 07-23-2009, 08:33 AM

If it will not shift at WOT --- the first thing to do is---- Change the fuel filter!

Of course there are other things that will affect it, but a dirty fuel filter is common.

thebeast02 · 07-25-2009, 01:52 AM

just thought id let everyone know i put me a new AC Delco fuel filter on today and my truck runs like brand new. no more shifting problems, and i finally got a K&N air filter

krashbros · 08-01-2009, 12:19 PM

I have an 03 LB&, same problem! I was afraid it might be the tranny. Would a bad fuel filter also cause the trunk to lose its prime? Every morning I have to reprime my truck. It starts right up, dies, then I reprime it and its good.

**DMAXchris** · 08-01-2009, 12:49 PM

I had this problem trying to run too big of a tune. A lift pump fixed me right up!!

Good info to put out there MM.