Hi!
After winter storage, I finally got my car out for a ride today.
It is a 65 Impala with a 5,3L/4l60e from a 2003 Tahoe. I did the swap last year, and drove a lot last summer without having any problems.
But today a weired problem occurred; when driving downhills for a while the engine starts to missfire and randomly stops! As soon as I put it in neutral or park, it fires straight up again. When driving up hills with part,or wide open throttle it runs perfect! Also when idling not driving.
The only difference from last summer is a cruise control switch that I mounted this winter, and I also made myself a gear range indicator on the dash. I've hooked onto the Transmission output selector A, B,C to encode the relay setup. This works very well.
The question is could this disturb anything that occurs missfire/shutdown?
Please let me know if you have any ideas..,!!

 

Does it fire back up while still pointing downhill? If not it might be starving for fuel, caused by the fuel pickup running dry on the downhill runs.

 

I don't think it has anything to do with the fuel pump/supply. The tank is topped up.

 

Oh OK. That wasn't mentioned.

 

Today I loaded in an older version of a pcm tune. After several test drives it actually seem to work fine....
I don't know what happens here, but anyway so far so good....
Thanks for reply "G Atsma"

 

You are welcome!