First Conversion Help Needed!

[mtbraun]

I was able to find another ECM, tried that with the same result. I suspected a power issue with the ECM and traced all my wiring to the power relay. I am running two relays, one Bosch style 5 pin for injectors and ECM power, and I retained the factory fuel pump relay. So when probing terminals on the power relay, I discovered that pin 87a had power when key off, but NOT key on or crank. Pin 87 did not have power at key off, but had power at key on and crank. Guess which terminal my ECM was wired to? 87a! So after I spliced the ECM power wire into terminal 87 the fuel pump cycled as it should and the truck started right up.

So now the question is, is that a fault in my power relay or is pin 87a only hot with key off?

[Six_Shooter]

Typical Bosch style relays will stick the connection of terminal 30 between 87a and 87. 87a being connected to 30 when the relay coil is not energized, and connecting 30 to 87 when it is energized.

So it sounds like your that is functioning the way it's supposed to.

[mtbraun]

Ok thanks for verifying. I don't mean to be critical of the resource here, as I am grateful for the plethora of information available to do this conversion. But could this post be modified to correctly explain how to wire the power relay?

http://www.gearhead-efi.com/gm-ecm-p...on-wiring.html

It seems this post has a critical error in explaining how to wire the power relay. As you can probably tell I can't read wiring diagrams like that on the power relay and was using the post as my direction. It might save someone a headache in the future.

[Six_Shooter]

Yeah that page is actually listing a Bosch M style I think they are called for "modified"... There are some that are the exact same physical shape, size and pin layout, but has two 87 pins, these were typically found with fog light kits. I don't know why the page would be written like it is, because those relays are atypical of what most people would find.

Thanks for pointing it out.

[mtbraun]

Ok so here's where I'm at. When I turn the key on the CEL flashes rapidly and does not stop. I tried another ECM and get the same problem. I also tried swapping PROM chips between the two, no change. The truck will start and idle, but its like in limp mode. It does not have any power, cuts out and sputters when you try give it some gas. The CEL turns off after the truck starts.

Here's what I all checked.

Traced all grounds, split off to engine/battery, no nicks and terminals are good clean connections.

I probed every pin of both connecters with key on and checked against the reference voltage indicated in a build thread wiring diagram. The only one that is even slightly off is coolant temp, at 3.65 volts. All others are right on.

I checked the CEL, has consistent voltage on positive side with key on.

When double checking the pins, I noticed that my connector does not have C2 (EAC). I'm sure I didn't remove this and do not think the harness had this terminal when we pulled it. I'm not sure if this would cause a problem or not.

I'm completely stumped here and have no idea how to proceed. I'm about to scrap this DIY harness and just buy one from AFI, but with this much time in it I'd really like to figure it out.

Please help.

Thank you.

[Six_Shooter]

Yes, your ECM is in LHM.

When you say you swapped the PROM, did you use a known good prom, or is this one that you have programmed yourself? What happens with the CEL when you install an OEM PROM (even if it's wrong for the application)?

[mtbraun]

I installed the PROM I got from Dave at Old School. I also tried an unknown condition stock PROM from the other ECM. No change in symptoms. I retraced the ALDL diagnostic and ground wires, both look fine. I thought maybe I fried the ECM since I had it wired up direct to constant 12v when the power relay was wired incorrectly. But when I tried a different ECM and got the same result I don't know what it could be at this point.

I ordered a new ECM and will have that in the morning. I hate to throw parts at it but I'm out of ideas. Next step will be a new harness.

[Thainglo]

Ok so here's where I'm at. When I turn the key on the CEL flashes rapidly and does not stop. I tried another ECM and get the same problem. I also tried swapping PROM chips between the two, no change. The truck will start and idle, but its like in limp mode. It does not have any power, cuts out and sputters when you try give it some gas. The CEL turns off after the truck starts.

I had the same rapid flashes recently after starting the car up with no chip in the PCM. Had been tinkering around on things and forgot to hook up the autoprom. The flashes were telling me the car was in limp home mode. Any chance you have something like that going on? Bad solder joints, or zif connection?

[mtbraun]

I'm not sure, but my CEL flashes rapidly with key on, but not running. As soon as the engine starts the flashing stops. I've officially pulled the plug on the DIY portion of this project and ordered a harness from AFI. Should be in early next week and I can hook up. I'll report back after that.