First Conversion Help Needed!

[mtbraun]

I finally got around to installing the harness in my first conversion attempt. I believe I have installed everything correctly based on Eagle Marks writeup and available wiring diagrams.

I used a 12v terminal block from my battery with fused lines from the terminal block to both the power and fuel pump relays. When I connect the terminal block to the battery, I can hear both relays momentarily "click".

Now, when I turn the key to "on" my fuel pump will not cycle. I've checked for power at the fuel pump/sending unit connection harness (new 87 GM model tank and sending unit/pump) and there is none. I then checked for power at the supply line coming out of the fuel pump relay and there is none. It's my understanding there should be power to this wire for a couple seconds while the system cycles the fuel pump. So I think its an issue related to my fuel pump relay.

Here's how I wired the factory fuel pump relay (from 91 Chevy donor truck):

Orange - 12v fused input from battery, also connected to ECM B1/C16
Black/White - system ground
Red - to fuel pump
Green/white - to ECM A1
Grey - to ECM B2

Wiring diagrams I have referred to says ECM B2 should be tan/white, but my ECM B2 was solid grey.

What I'm still confused on is the wiring diagram shows ECM B2 connected to the fuel pump relay and then on to the pump. If that is the case then what do I wire the fuel pump relay red wire to? I cannot find a wiring diagram for the 1991 fuel pump relay. The build threads I have read only reference four wires for the fuel pump relay. I didn't take good enough notes when disassembling the stock harness on this particular item.

And lastly, when I turn the key to "on" my SEL flashes 7 times and then turns off. It does not stay on when the key is on. I verified that it is wired to a circuit that has power with key "on" but not crank.

[mtbraun]

I think I may have figured this out. I found another build thread and problem feedback that showed a fuel pump relay diagram. I think the red wire from the fuel pump relay should be left unconnected as it is the test wire. The grey from my fuel pump relay should be tied to B2 and the brown wire from the oil pressure switch. I did not have the oil pressure switch installed because it wasn't referenced in the build thread or wiring diagram I was referencing.

so the only remaining question I have is where do I connect the grey wire from the oil pressure switch. It is fused so I presume this needs to connect to power somewhere, just don't know where.

[mtbraun]

Update - I corrected my wiring error and installed the oil pressure switch with its wiring. The tan wire from the oil pressure switch is currently unhooked as this is for the dash display.

Anyway, when I turn the key on the fuel pump will not cycle. I can cycle the pump from the test port on the fuel pump relay. I went through the troubleshooting diagram for code 54 Fuel Pump Circuit and when I try to test the circuit between 465 (green/white wire from ECM) and ground, after turning on the key the circuit does not show power within two seconds. The troubleshooting guide suggests a open circuit 465, short to ground, or faulty ECM. I have traced the wire from the ECM to the fuel pump and all looks fine.

Now here is where it gets weird. Every time we turn off the key, the fuel pump will cycle for approximately 2 seconds. The fuel pump will not cycle when the key is turned on, only immediately after it is turned off.

In addition to this, when I turn on the key, I still get 7 flashes on my SEL. Does this suggest a faulty ECM?

We tried jumping pins A/B on the ALDL and then the SEL flashes 2 times. Also, for whatever reason as long as the ALDL pins are jumpered the IAC valve extends into the throttle body. The only reason I noted this is I heard a faint sound from the engine when we jumped the pins. I'm not sure if that means anything or not.

Really need some help here.

[Six_Shooter]

Yeah, there's something up with the ECM or the way it's powered.

When you turn the key on, there should be a single flash, and then stay on until the engine is running.

[mtbraun]

I'm going to grab a different ECM. Question - when grabbing another 1227747, do I need to switch the small chip from the old ECM if the new ECM is not from the same size engine? I have a burned PROM chip already.

[jim_in_dorris]

I would try a stock chip first, you may just have a bad chipburn. If you do switch the ecm, for test purposes, leave the old chip in until you verify the cel blinks properly

[mtbraun]

so my local u-pull has a tub full of ECMs but no 1227747. Are there any quick options available to use a different ECM with my burned chip? I think the answer is no but wanted to double check before I bought another 1227747. I don't have my stock chip as that was sent to dave when he burned my new one.

[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.

[Six_Shooter]

Yeah, probably not an ECM problem, especially since you tried two different ones with the same result. I think over the time I've been playing with Delco EFI, I've seen 2 failed ECMs, and one wasn't fully faulty, just didn't work correctly all the time. It would work correctly most of the time, then just randomly not. We traced it to grounding the ECM case to the body, which is a big no-no with OBD1 Delco/GM ECMs. We ended up going with a completely different ECM for that swap in the end anyway.

The other was in my Datsun (also a Delco ECM), and I saw one tiny drop of water fall onto it from under the dash, while driving through a heavy rain storm. I didn't think it went in, but then the car started to sputter and ultimately failed to run, because I had the wrong MEMCAL for proper LHM duties, swapped the MEMCAL for a closer match and LHM worked, but then so did swapping the failed ECM out in that case. lol

You need to use a known good PROM, FOR your ECM to verify. A random unknown PROM could be for a completely different ECM and would still cause an LHM situation.