My neighbor is an old school hot-rod guy and decided he was going to build himself a TPI motor. He cut up a wrecked 350 F-body and swapped the intake, wiring etc to his existing 406 SBC he already had in his car. It ran horrible and I got the call to help. I am fairly good with TPI stuff, but not MAF and not on a modified motor so I'm throwing this out there to see if the collective can help us out.

YES, I know he is going to need some MAJOR ECM tuning for this to run optimally, but he is just trying to get it going on the stock setup to confirm everything works. No codes in the ECM

88 STOCK TPI setup and ECM. Everything is setup bone stock as far as wiring, ECM, fuel pressure etc.

The problems:
Runs horribly rich at idle. Makes your eyes water rich. Doesn't start all that well either. Fan is always on too.

The data:
Scanner shows 02 acitivity, but never saw it go above .6 volts. He is replacing the 02 sensor today. MAF showed something like 25 g/sec. Injector pulse width was like 3.0v-3.2v. Both of these numbers seem high to me but I'm comparing to a stock MAP car.

What we did:
Verified fuel pressure, key on motor off: 41psi
Ignition wires, plugs, timing are 100%
Unplugged the MAF sensor to put it in limp mode. This killed the engine out for a few seconds then it went right on to running horribly rich.

So, I'm pretty much lost here. My GUESS is the motor sucks down so much more air that the MAF reading are out of whack and the ECM is fueling like mad to keep up. But, if that were the case, unpluggin the MAF should have helped.

Thanks for your help!

 

My 350 pulls about 8 g/sec at idle. No way a 400 is using 3x as much air at idle. If the computer THINKS it is, that would easily explain your rich condition. This is where I think you need to concentrate your efforts. Make sure all of your connections are clean, and if possible, try a different MAF.