Hello All,

It's been a minute since I've been here, but hello. I've been working on a power-train swap (1991 5.7 liter TBI engine into a 1987 Jeep Wrangler) and I made a mistake during the wiring portion. I reversed polarity feeding the GM TBI ECU for several hours. Lets not talk about how that happened, except to say there was alcohol involved. Lesson learned. Anyhow, ordered up an new ECU, because I couldn't get the old one to do a single thing after the reverse polarity. Was completely unresponsive. I carefully transferred over the PROM and CALPAK (already pulled and reinstalled them - checked for bent pins) from bad to good ecu and now I have the expected code 12 and then after it flashes a 51. I'm assuming I also destroyed the custom PROM chip aside from the ECU itself. Is that an accurate assessment? I have not tried to run the engine yet.

 

If it was the same service number ecm
sounds like the prom Is bad.

 

Thanks so much for the reply. I figure the PROM is smoked as well. I ordered the replacement ECU from rock auto and transferred the PROM and CAL-PACK over to it. The smoked ECU was a 1227747 I got off ebay 13 yrs ago and the one I got from rock auto was supposedly the same. When I ordered it their page said their part was equal to a OE 1227747. I'll try a new PROM and go from there. Thanks

 

What does the SES/CEL light do at key-on, engine-off?

And yes, connecting the battery reversed with a C3 ECM ('7747, '8746, and a bunch others), fries 2 diodes and a trace. Have repaired a bunch of them. Never had one take out the PROM, but there is always the first time.

RBob.

 

Hello!! Key on, engine off the fuel pump primes for 2 seconds, SES/CEL light comes on solid and bright for about 1/2 a second and then begins rapid flashing. Turn key off, flashing continues for about 4-5 seconds more till stops. Can repeat every time.

 

Fast flickering SES/CEL is a checksum or MaskID error on the PROM. So either the PROM is bad or it isn't the right ECM. Can check chip U7, last 3 digits of the part number is 434, for the '7747 ECM.

RBob.

 

Hi again. What is chip U7? Is it inside on the motherboard? I only know enough to be dangerous on these systems.

Edit: I found chip U7 in the old ECM. I will look inside the new ECM and verify I have that part number U7 chip. Thank you.

Verified last 3 of the U7 chip were 434, but I ordered another used non-reman 1227747 ecm from ebay anyhow. I dont trust this rock auto cardone reman. Looks like someone sprayed some kind of coating all over the motherboard. Must be part of the “reman” process. Well it looks terrible. Ill save it if it turns out to be a good ecu. I did find at least one thing that killed my other ecm. A melted section of solder circled in red below. Such a waste of a perfectly good ecm.

 

So no use?

 

Read post #4...

 

PROM was also bad. New ECU works perfect with a new PROM.