I'm absolutely stumped at this point hopefully someone can help me out. 94 K5 Blazer, 350 TBI, can't get it to start under normal conditions.

When I turn it on, the fuel pump relay does not turn on. The relay itself is fine, and bypassing the relay activates the fuel pump. I can activate the relay by installing a jumper between E-16 and F-6 on the blue ECM connector. The injectors are also not firing. I have tested them independently and they work just fine.

I want to rule out the ECM as the culprit, but the fact that it is not activating the fuel pump relay with the ignition ON is throwing me for a loop. I bought a replacement ECM that was supposed to be plug-and-play, but it required the PROM from the old ECM, and installing the new ECM with the old PROM is still causing the same issues.

I just got my truck back from the shop about 3 weeks ago, and it ran great until it suddenly died on the freeway at 75mph. I just got the engine replaced, which was a nightmare that spanned 4 engines over 3 years. The last thing that happened at the shop was the positive connector on the alternator broke and shorted out to the case, which fried multiple grounds attached to the engine. Could that have damaged the PROM? New components on the truck are: engine, distributor, exhaust manifolds, O2 sensor, fuel pump, fuel filter, gas tank, engine temp sensor, both injectors, starter, alternator, and I'm sure there's more that I've just forgotten at this point.

EDIT: I forgot to mention that I am getting an ICM REF High signal at the ECM connector, confirmed with a test light while cranking. The only other signal I checked is the fuel pump signal, which shows 12V when the fuel pump relay is jumpered in the ECM connector.

 

pour some fuel in the throttle body and see if it fires/runs

 

Yes, it runs if I manually add fuel. The current problem is the injectors do not fire regardless of whether the fuel pump relay is bypassed or not, and the fuel pump relay is not being activated when the key is turned on. All the wiring is correct and I can get the injectors to fire by grounding them at the ECM connector, and I get get the fuel pump relay to activate by powering it at the ECM connector.

I ordered a new ECM and I'm still having the same issues with the new one, bit I had to transfer the PROM from the old ECM to the new one. My question is whether or not the PROM could have been damaged by the alternator short, or is there some other signal the ECM is supposed to get during IGNITION ON condition to activate the fuel pump relay.

 

I think you are on the right track with the ecm replacement.

 

Any kind of security system (anti-theft) on this vehicle?

 

There used to be one installed but it was ripped out ages ago

 

New ICM with new distributor?

 

Not sure, but I did hook up a test light to it and it is sending pulses to the ECM properly.