A buddy and I put NOS on his LLY this weekend and it seemed to pull hard until the 3-4 shift then the truck just seemed to lay down. Any ideas?

His setup:
Predator Custom Tune (100+) + VA
.54 jet
Nitrous Express Large solenoid

We did purge the system everytime before running it.

To the best of our knowledge, the trans went into "lay down" mode.

At first we thought it was fuel starvation, but we see the ECM command less fuel sometimes after the 4-5 shift. Truck has very low power after that, and recovers after the pass is over.

If you can, try not to spray during the 4-5 shift.

He has a SC IV transmission. Will it still go into laydown mode?

Our Suncoast III will laydown if I spray through the 4-5 shift. If I turn off the spray at 3100, then let it shift, then spray again, it works fine.

it seemed to do this with out the NOS too, but not nearly as bad. After the 3-4 shift the EGTs would actually start to drop? - does that make any sense?

My truck was doing the same on earier shifts, but fine on 4/5 shifts. Put the ppe on with the higher rev limits and problem went away. Still not sure if trans is not doing it's job allowing the higher revs, or if the tcm wasn't liking the extra power and delaying shifts. Next time watch your tach, mine was laying down because of not shifting in time. PPE fixed the laying down problem, but I still might have tranny work ahead.

Rob

Yep. If you have a Tech II, (or Predator?) watch the Main Injector Shot mm3, this is how much fuel the ECM is telling the injectors to spray. It drops to about 1/2 of normal and freezes (55 mm3?). If you try to spray nitrous, there is not enough extra fuel, and it does NOTHING. It feels like the bottle is empty but it's not.

so the fix to this is???

Not sure yet. I put an ATS trans in the White Truck, but still needs some "fine tuning".

When I figure it out, I'll let everyone know. This problem is what kept us from running a 12 in Big Blue.