Quote Originally Posted by neo View Post
So, as i suspected, you can and do get a very clean nice tach (5v square wave) from the crank position sensor. The wire that provides the signal is the light colored (yellow or white on the harness) one, it is on the end. The opposite (3 wire hall effect sensor) is grey iirc and that is source 5v, the middle (black?) is ground. The signal is super clean and perfect for the tci tcu.

I am suspecting the fix of the cps now tells the old pcm that the engine is running and tries to shut the fuel off over 900 rmp. This is pretty bizare. It now seems the best thing to do is keep the pcm in the dark and cut the cps signal so the p m doesnt know the truck is even running?!? Any suggestions? Thanks to all!
Neo
Thanks for your followup. Most don't use the CKP (Crank Position) sensor for a tach signal because it requires a regulated 5vdc to operate. This 5vdc is generated by the PCM, which is sometimes disabled after a conversion to MFI.

The CKP generates 4 pulses per crankshaft revolution, where the oil pump drive generates 8 pulses per revolution, but it turns at half the speed of the crankshaft, so the net effect is the same. The oil pump drive is just a simple 2-wire sensor, so it is easier - usually - to adapt to an aftermarket transmission controller. That's what I did in 1999 when I installed a Jet 4L80-E in a non-electronic truck. Worked great.

Jim