Fuel 87GT fuel pump priming / ECM pin 22 question

TimC

Member
Apr 24, 2022
8
2
13
Illinois
Bone stock 87 GT car ran and drove fine last fall when I put it away for the winter. I replaced the battery this spring. Fuel pump does not prime when I turn key to On. When I jumper the fuel pump at the test port, the pump runs, and the car fires right up. I do not want to drive the car with the test port jumpered, and ignore the problem.

What I find unusual is that when I check the wiring at the fuel pump relay (with the relay removed) the Tan/Light Green wire has continuity to ground with the key on, and the engine not cranking. It seems that the ECM is sending the ground signal as long as the key is on, even if the engine is not cranking or running. I have removed the 60 pin ecm connector, and the ground signal at the fuel pump relay connector goes away, so I believe that the Tan/Lt Green wire is ok. This leads me to believe that the trouble is within the ecm. It is the original Ford ecm, with seal still attached.

I suspect the relay is fried, at this point, but I am concerned that just replacing the relay, and not diagnosing the constant ground at pin 22 will just fry the next relay.

I have read MANY threads on here about fuel pump and relay issues, but have not found any threads relating to constant ground signal at pin 22 of ecm. I'm new to Stangnet, I'm not new to Mustangs.

All suggestions appreciated.
 
  • Sponsors(?)


General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
23,103
8,442
203
polk county florida
Knowing the age of these cars I would send the computer to the ECUExchange to get it checked out and updated.
 
  • Like
Reactions: 1 user

TimC

Member
Apr 24, 2022
8
2
13
Illinois
There is 12 ohms of resistance between pins 22 and 40, as well as between 22 and 60 on the ecm
 
  • Like
Reactions: 1 user

TimC

Member
Apr 24, 2022
8
2
13
Illinois
Thank you. 12 ohms, as measured by my analog VM... Jr. is "borrowing" my DVM.:)

I was tempted to open the thing up and inspect the caps and traces, but I don't have the correct socket to open it up. 4mm is just a wee bit too large. Screws are not SHCS on this ecm.
 

TimC

Member
Apr 24, 2022
8
2
13
Illinois
Update: Sent the ECM to Ecm Exchange. Reinstalled it with no change. Fuel pump does not prime when key is turned on.
What's next?
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
38,936
14,849
224
Massachusetts
There is 12 ohms of resistance between pins 22 and 40, as well as between 22 and 60 on the ecm

I know this is a bit late. I checked on a spare a9l I have sitting around. No resistance or continuity from pin 22 to 40/60

Sounds like your pin 22 was shorted to ground before.

What you can do is poke a pin through the wiring at pin 22 at the ecu. Put the multimeter on the pin and the other lead to ground. Have someone turn the key to on and see if you get continuity to ground for 2 seconds for the initial pump prime.

My guess is there is still an issue with the ecu
Not priming the pump