Now we move into desperation territory (seeking advice)...

[gmbellew]

1989 1990 1991 1992 Chevy GMC Truck Engine Computer ECM 1228747 5.7L 7.4L | eBay

This ECM will fit any application that originally used the 1228747 ECM. GM installed this 1228747 ECM in a variety of GM applications. This was possible because each model received their specific PROM (also known as chip) from the factory.

www.ebay.com

you will just have to swap your PROM to the new ECM.

 

[gmbellew]

Fuel pump relay has been replaced. I swapped it as an outside chance it could be causing an excess electrical draw/voltage sag. I'm not losing the fuel pump itself (I even jumpered the oil pressure switch to force an always-on state and still had it shut down).

When it went into the second failure mode of spitting back through the air cleaner at any amount of throttle, it again cleared itself after a power cycle.

I was thinking to ONLY power cycle the fuel pump instead of cycling the key. Just trying to narrow it down. link to new ECM above. that's the same vendor I got my spare ECM from when I thought maybe my ECM was bad.

 

[YakkoWarner]

I don't know any more than what I read on their website from doing some research. But if you just want to see what the ECM sees at the sensors, how it is adjusting fuel, RPM, etc, I've been pretty darn pleased with ALDLDroid app on my phone and a Bluetooth ALDL cable from 1320 electronics.

Havn't been able to get back to this for a bit - life intervenes.....

How do I find these 1320 electronics people? They don't seem to have a web site, their YouTube channel has 5 videos posted a decade ago and no contact info. I think its pretty clear I need this kind of tool if I want to try to save the TBI system rather than carb swap, but all appearances indicate they have been intentionally removed from circulation. If they DO still exist, I'd love to know how to buy this...

 

[YakkoWarner]

1989 1990 1991 1992 Chevy GMC Truck Engine Computer ECM 1228747 5.7L 7.4L | eBay

This ECM will fit any application that originally used the 1228747 ECM. GM installed this 1228747 ECM in a variety of GM applications. This was possible because each model received their specific PROM (also known as chip) from the factory.

www.ebay.com

you will just have to swap your PROM to the new ECM.

I wonder if we just discovered the problem: That link is for an 1228747 unit, my truck seems to have (upon visual inspection) a 1227747 unit. Did someone swap in the wrong ECU??? Is there any way to determine which ECU I am supposed to have?

 

[gmbellew]

I wonder if we just discovered the problem: That link is for an 1228747 unit, my truck seems to have (upon visual inspection) a 1227747 unit. Did someone swap in the wrong ECU??? Is there any way to determine which ECU I am supposed to have?

There might be a sticker under the dash by the ECM that has the number in case somebody installed the wrong one? But I'd think you'd have larger drivability issues with the wrong computer.

Could also be that they swapped ECM with the new body style and those got a different computer. Might have to research to see which is correct