My LB7 has had something going on with the trans since the time I purchased it last August and 13,000 miles ago but I never really thought much about it. When I accelerate heavily on it all of the lights will surge and dim out, it usually only happens under heavy acceleration and around 5th gear and overdrive, when its getting close to the next shift, I havent paid attention to the volt gauge while this happens to see if my voltage is dropping or not. When I bought the truck it still had a stock trans in it, although I was told it was not the trans original to the truck. Previous owner told me the trans had been replaced and only had 160xxx miles at the time I purchased it. It continued to do the light surging even after the trans was pulled and rebuilt to Suncoast stage 3 specs. This being said the only thing that I could think of is that something is bad in the TCM causing the trans computer or trans itself to pull too much power when its trying to shift under heavy acceleration. Sorry for making this post so long haha, pain in the ass to explain, thanks in advance.
Allison 5sp: TCM Troubles?
- Thread starter AThomasLB7
- Start date
Truck is a 2003 LB7, EFI Live with IdahoRob Tuning, K&N Cold Air Intake, 5" MBRP Straight Pipe, Stage 3 Suncoast Trans
Loose solder inside the cluster. The TCM has no control over the lights other than a class 2 data message sent via j1850 bus over the vehicles databus for gear display and trans temp.
Its not just the cluster lights that dim, the headlights will go dim and surge, the tail lights, all the interior lights, I'm guessing something is bad in the tcm and pulling large amounts of power to make those shifts. I'm gonna try and get it to do it tonight and see if its pulling my voltmeter down substantially.
Check all of your grounds, start with the one under the drivers door and the ones on the drivers side of the engine
The TCM is on a 10 amp fuse, it couldn't pull that kind of power if it wanted to. Check the grounds, espescially the ones under the drivers side floorboard. Check the connections at the alternator, and also check for rubs or chafes on any battery cables. Also since you say it's happening at high rpm's, try revving it to the limiter sitting still with everything on and see if it does it. Sometimes when the brushes get worn in the alternator, the can skip at high rpm's, and cause it to stop charging.