Yet Another fuel pump relay situation 1980sc

[Rennguy]

Hey Boys and Girls, I have a 1980sc that developed an issue while sitting over the past few months, FYI It ran fine prior to. The Fuel pump is only running when the key is in the start position. I have diagnosed the crap out of it and have isolated the problem to a constant ground on pin 85 on the FPR. I have disconnect the Air Meter Switch and the Rev limiter and the issue is still there. To my knowledge this only leaves the Alarm left on that circuit. Or a bad wire in- between but since the car ran fine when parked i’m betting against that. Does anyone know where the Alarm wire that goes to pin 85 of the FPR originates? I’m assuming some type of module, but I can’t find any wiring schematics to confirm this. Also, i have taken another relay and cut off Pin 85 and the car runs great, with the obvious situation of the fuel pump activating with the key in the on position. Any help would be greatly appreciated as i’m on a mission to fix this the correct way.

[PeteKz]

I'm not sure what your problem is. Does the car not start, or fires briefly and then not run?

During the start sequence, the FP should only run when the ignition switch is turned all the way to Start. Once the engine starts, the safety switch on the air metering unit should open allowing the FP to continue running. What exactly is happening is important becuase it points to what part of the sequence is not occurring.

Offhand, I think your relay may be stuck internally. Try swapping a round relay from some other location. The black ones work the same way as the red ones for troubleshooting purposes.

[Rennguy]

Hi Pete, thanks for the responce.
- car only runs when key is engaging starter
- dies when key is in on position
- pin 85 on Relay has ground in both key positions
- i have disconnected the safety switch and the rev limiters and it still has a constant ground on pin 85
- pin 85 needs to be open when key is in the run position to stay running.
- something is grounding out pin 85
- the only other item indicated on wiring diagram connected to pin 85 is the alarm system(alarm, safety switch, rev limiter) i have disconnected SS and RL.
- i need to find out where that alarm wire going to pin 85 originated so I can unplug it to see if ground connection goes away, if not i have a short to ground in a harness.
- from what I have read the alarm box doesn’t appear to have pin 85 going to it, so where is it coming from?

[harv666]

Do you have an immobilizer or alarm installed in the car?

[Rennguy]

Only the factory unit and i believe that is the issue. That is why I need to find out where the alarm wire going to pin 85 originates. Based on the diagrams I have seen, the black alarm box does not go to pin 85. But my factory manuals clearly shows a wire going from 85 to “alarm System” (see drawing)but i can’t figure out where it is going.

[Rennguy]

I just found the plug indicated on the diagram above, it was hidden under the fuse box, unplugged it and bang. No more ground to Pin 85 and the car runs great. But, i still want to know where this wire attaches to the alarm system so can actually find why it’s getting a ground signal.

[Snwmble]

Wondering if what you did will solve an intermittent issue I’m having. I know it’s something tied into the alarm in my case. Once out of every 50-100 start ups, i will hear a relay clicking when trying to start the car. It sounds like a relay clicking behind the dash (which is where i believe the brains of the alarm sit). The car won’t start in this case


What works for me every time is to pull the fuel pump relay and reinstall back into the fuse panel, and it starts right up. Do you think what you disconnected will bypass this issue? I was thinking of wiring in a toggle switch to the fuel pump relay to avoid having to remove/reinstall until i have time to properly fix.

[Rennguy]

By pulling the relay and reinstalling it sounds like you are resetting something… maybe the alarm control box? I know very little about the alarms on these cars. I still don’t know what this wire I unplugged goes to. I know it’s for the alarm system but i don’t believe it goes to the alarm control box. BTW, my situation was also intermittent and then it wasn’t. When yours acts up, does it try to start when the key is in the start position and then dies when the key returns to the run position?

[Snwmble]

Yea when i try to start the car it tries to start and dies, then immediately after i hear the relay clicking as if an alarm is going off, but doesn’t honk since i had removed the alarm horn. I hope by me disconnecting what you did, it will allow me not to continuously remove that fuel pump relay. Its so annoying!

[Rennguy]

Give it a shot, nothing to loose.

[Rennguy]

Come on…. someone must know where this wire goes.