Burning Star IV

Well maybe I am missing it somehow in the books I have, but I am having trouble finding which pin location on the ECM is for engine rpm signal? I am using a Delco 7730 equivalent ECM. The exact part number eludes me right now. I am also using MSD's drop in replacement destributor part number 8633 I think. I would think one of the wires from the four wire connector would go straight to the ECM for rpm, but I can not determine which it is.

Also what does the ECM do to turn the fuel pump on? Does it ground the fuel pump relay or does it send power to switch on the fuel pump relay. I figure it grounds the relay like all the other relays, but I don't want to assume and I am not finding that info either.

Thanks everyone for any info you can provide. Sorry if this has been covered many times before and I simply chose the wrong search words. I also hope I have posted in the correct forum please move it if I have not.

RBob

iTrader: (1)

The RPM signal is usually labeled as REF+ or REFERENCE. It is pin D8 on the ECM. There is also a REF- OR REFLOW (D9) that is the ground side of the reference signal.

The fuel pump relay drive provides +12v to the relay. This must be on pin D of the relay. Pin F goes to ground.

RBob.

Burning Star IV

Ah, I had forgotten about the reference ground. That will need to be connected as well, correct?

Any idea as to why GM had the fuel pump relay being supplied a 12 volt signal by the ECM instead of ground like the other relays? Just curious.

I am using aftermarket relays so I don't have pin letters, just the switch coil.

Thanks

Burning Star IV

Well this is what I get for having my computer and the vehicle in two different locations. I completely asked the wrong question. I am wondering about the fuel pump signal. Pin number E13. If I have my information correct this line connects to the positive line going to the fuel pump and the ECM turns the pump on for those two seconds at the very beginning with this wire. Once the car cranks, the ECM then switches power on to the relay and turns this line off so that power to the fuel pump is coming from the power source not through the ECM. Am I right?

Also I need info on the coolant fans. The ECM sends power to the relay to turn the fans off and grounds that same wire to turn the relays on consequentially turning the fans on. This is pin E8 I am refering to. Is this correct?

I am using a premade harness with this vehicle. It is not a thirdgen. I am simply using the 7730 computer to control everything. I also had to cut the harness apart and extend it to meet my needs. I also prefer to understand what it is I am doing versus just connect some wires and cross my fingers. This is why I am having so many questions. I appreciate evryones help. Thanks

RBob

iTrader: (1)

The fuel pump ECM pin E13 is an input to the ECM. It is used to measure and report via ALDL the voltage going to the fuel pump. this allows the ECM to test the FP relay.

At key on, engine off, the ECM turns on the FP relay for 2 seconds. Then as long as DRPs are seen the ECM turns on the FP relay. If the engine stalls, after 2 seconds and the ECM turns off the FP relay. Although the fuel pump won't stop running until oil pressure is lost.

Head over to www.diy-efi.org/gmecm

Click on ECM info, then the 1227730/1227727 link, head to the bottom of the page, grab the '92 f-body TPI pic's. You can thank me later

RBob.

Burning Star IV

Excellent! That web page is better than the info I have. From those schematics and from what you said I see that the fuel pump relay is turned on by the ECM and power comes through the relay and goes to the pump and back into the ECM. That makes sense. Thanks.

busta9876

Safety is only thing I could figure out.

A short to ground on the relay control lead might be more likely then a short to power in the event of a crash.

If a crash somehow caused the fp relay to kick in, FP could stay running even when the car was off..

Thats my best guess.