explotions?

last week I was racing in the sand 1/8 of a mile In 4WD LOW, no NOS.. anyways.. a couple of buddies kept telling me that everytime I raced, when I got to the shifting point, it looked like I was shooting a darn .45 caliber gun out of the window LOL! one loud detonation in every shift point.. btw I couldn't hear anything because I had my windows rolled up.. What I remember is that the truck died at the top of every gear.. then shifted and did the same thing at the top of the next gear..
what can be the reason for the truck to do that? tune or what? after that night the Crank Relearn DTC showed up..
thanks!

detonation?

yes sir, that's what I was trying to say.. :)

my guess is it's running out of fuel up top and going lean

4-LO isn't mean to be shifted in, so it will only shift at WOT.

This is because the VSS isn't reading a fast enough pulse.

Not sure if thats the reason. IF you are going to continue to do this, there is a pin that you ground on one of the harnesses (orange in color) that will allow your truck to shift while in 4-Lo.

hey buddy thanks! what do you mean by "4LO is not meant to be shifted in" I didn't uderstand that.. all of my buddies with this kind of trucks race in the sand in 4LO and never have that problem.. or at least not that I know or haven't seen it.. but how would that procedure will help? and can you help me out with that? do you have a link in how to do that pin-harness thing? thanks a lot!
btw a mechanic said that the truck was saying those detonations might be because of the PCM being tuned for NOS (timing) and me running without it..
what do you guys think?

Same trucks and transfer cases?

Let me see if i can find that info again.

Heres a link to one article on GMFS. Main topic is about swap, but scroll down and you will see the discussion of pin grounding.

Question NP246 to NP241 Swap - GMFullsize Forums

Leavin work in a few, i will try to find some more info and sent it your way.

hey bud, my truck does shift in 4LO but hits the rev limiter every gear and does that detonation..
did you find any more information about the pin-ground thing?
thanks I appreciate!

as far as i always knew 4 lo was just for first gear and not supposed to reach over 35 miles an hour but idk maybe thats just BS.

It does run way more than that man.. most of the people around my hometown, fix their trucks for sand racing... 1/8 of mile, and most of them race in 4LO.. I´ve tried to race in 4HI and they just BEAT me by faaaaar, when I change to 4LO like they all run.. the story changes :)