Hi All,

My 400SBC 24x project went to the dyno on Monday and unfortunately hit a wall.

The tuner couldn't tune out an issue when the transmission changed from one gear to the next.

The car is bogging right down, coughing, spluteering, backfiring etc for about 4 seconds before it comes good.

I'm working through the possible causes one by one, but on a test drive I just noticed the transmission won't manually change at all.

I have to put it into 1st or 2nd to take off, then if i put it in drive it will automatically just straight to fourth.
If I leave it in drive and slow down the car will jolt and jar like the trans wants to change but is locked in gear.

So symptoms are:
* No automatic upshifts
* No downshifts at WOT
* No DTCs thrown
* Hesitation, backfiring and stuttering when manuall changing gears


A couple of questions:
What exactly is LIMP mode? I'm assuming its basically the electronic part of the trans is not working at all and it just works off manual changes, or is it something else?

Secondly, is there a diagram of the transmission connector for a 96-97 4L60E anywhere I can use to check each pin to see if it has power/ground/pcm wiring correct?

And lastly, would this be the reason for the hesitation, backfiring etc on the tune or am I chasing multiple goblins here?