OK 305 TPI to 350 TPI, using the same trans. Before the swap, TC lock up was fine. Now after the swap, it hunts from about 38-52 MPH, then finally stays locked up. While studying the FSM, it shows that a 700R4 behind a 305 has a 4th gear switch that is NO, while a 350 has one that is NC. It also shows in one of the diagnostic flow charts regarding TC lockup problems that one issue could be an incorrect PROM. Of course, part of my swap was going from an AXXB, (305), PROM to an AUJP, (350), PROM. So, how do I find out which switch I have right now? How do I determine what I need? I sure as hell ain't gonna' swap PROMs back as I just spent $450 for a tune/dyno session and the AUJP cost me $75, to boot. I had originally thought it was a state of tune problem. HELP!

 

If you kept the same trans. and wiring and changed nothing but the engine itself, the NO/NC is irrelevant.

You sure as hell are gonna put the AXXB in, so you can find out if lockup works. If it does, it's your tune and you can go ask them to fix it.

Easy.

 

Well, now that you put it that way, yeah, I will. I didn't even think of that.

For education sake, how would the tune affect it? It was still acceptable with the AUJP before the tune albeit ... "different" than the AXXB. Is it something he did directly or a result of adjusting something else? I'll just add this to the list. I was gonna' go back anyways as the car runs really well but the idle is a little high/unstable.

 

Lockup is determined by the ECM based on input from the VSS and TPS as well as possibly temprature. The 4th ear pressure switch is included in the TCC circuit and on some wiring setups it provides feedback to the ECM; some it doesn't.

The tune could aggressively unlock with minimal TPS change, or conservatively stay locked more. Back to the tune itself. Won't hurt a think to drive it 10 miles to test lockup with the old PROM. On the other hand, you could tap into the TCC command wire to see when the new PROM is commanding lockup too.

 

Gotcha'. Thanks for the info. I'll swap them out one day this week to see what happens.