I have been involved in a TBI 454/4L80-E swap into an '83 Suburban, and I am having a bit of trouble.  The engine was installed using an aftermarket harness and a GM PCM.  The engine barely runs.  I have replaced the EGR valve, MAP sensor, fuel pump, and IAC motor. I have checked and rechecked all connections, and have had the same done with another set of eyes. The vehicle sets no trouble codes, although I can force it to set codes by unplugging a component, which leads me to believe the SES is functioning properly.  I have had a TECH 2 on it, and all components seem to be functioning within parameters-at least as far as I can tell on an OBD-1 system.  It is making 17 inches of vacuum on the rare occasions it will idle long enough to check.  I know this type of thing is tough enough to diagnose when you are standing next to the vehicle, but does anybody have any ideas?  

It's good you realise your only gonna get suggestion on this thing.U put this BBC in place of a diesel,or sbc.If diesel exhaust i'snt a prob most likely.If sbc,U the stock exhaust may b to small.2" single wont run a healthy BBC.U need at least 2 1/2" on BBC.Thats just to get the minimum requirment's.Cammed,or HO needs a *** of a lot more.Also is the TBI for 454?4.3's&350's have the same TBI but BBC differs.I dont know if that would throw a code or not.I know the injector orific's are way dif.so the thing would idle real bad,if at all.You prob.here this a bunch,without bein there as u sayed all we can do is suggest.Only thing Im sure uts not is vacuum.Could b dist.timing way retarded.TPS could b fouled into open loop.Sometimes these last 2 WONT throw a code.Had an 89'S10 4.3 TBI,TPS went,no codes.Wouldnt idle,flatspotted on slight throttle,stomp it to the floor itd run like bat outa-.Stuck in open loop.  

I think I got it.  A new fuel pump was purchased from the auto parts store, and it is for a small block.  According to the GM manual, the big block has a specific pump which runs at a significantly higher pressure.  I rigged one up last night temporarily, and the truck ran great, idled in gear, the whole deal.  I'll know later today if I got it whipped.