Hello new here and need some help, I am shaping a 350 tip in 1956 Chevy and I have no injector pulse now. Back ground I stared with 1985 IROC donor car removed the 305/700r4 - was not running and partially disassembled when removed. so I now have a 350 gm performance engine with the tpi manifold, 24 lbs accel injectors, new distributor, repined harness following chevythunder, cardone165 ecm with APYU prom, vats bypass chip I bought from amazon. I cannot get the car to start. I have spark but no injector pulse. I have 42lbs of pressure at the fuel rail and get 2 sec prime pulse. I cannot get my my snap on solius scanner to communicate with the ecm using adapter and I only get a code 12 when I check the old way. I have 12v KOEO to both sides of the injectors, all grounds ring good, The only thing I can find that is not within specs is I have 12v to the natural safety switch orange/blk wire at KOEO. I disconnected the power to the vats and still did not get a code. I bought the prom from a local junk yard, but I am not getting a PROM code either. Any suggestions or help would be greatly appreciated.

By prom code do you mean scan I’d off the prom ?
The vats bypass chip you purchased is it on a piggyback adapter or is this a hz modulator that connects to the ecm ?

The number on the MEMCAL casing is 3516APYU. 50Hz modulator stand alone description below

Timers.Shop GM VATS PASSkey II Bypass Module for LS1 and LT1 Painless

Feed the signal to pin b6 of the ecm. If it’s duel frequency it might be 30hz instead of 50.

It is wired to pin B6 - I will try changing to 30hz, Is there a reason I did not get a code 46 when I removed the 12 to the modulator?

I’m not sure what it takes to get a code 46.

From the list I have code 46 was for Vats malfunction. I remember that codes are not always set in the early systems. Could anything else besides VATS climate the injector pulse? Since I have never had this engine running prior and I have chased most everything else that I could find tests for, could the base timing be far enough off to effect the injector signal?

Could be a open in the icm from the purple/white wire to pin b5.
Bad icm. No power to the injectors. Injector /ecm ground.
or vats or bad ecm

Timing off will not effect the injector pulse it will still be there.

ok, going to try changing the hz signal today. All the grounds and purple/white wires ring out for continuity. I have replaced the icm twice since I thought I might have shorted the first one.