Fuel Pump Diagnostics Options

[solex]

Hi All,
Need a little help to diagnose a fuel pump problem in a 75, I do not hear the pump when I turn the key to the run position.

The car was running, I had a few occasions where it would not start, let it sit for a few days and it was start right up.

The grounds: under the relay board, battery and transmission have all been cleaned.

All fuses are good.

The relay is working as I can hear it click into position.

When the key is in the run position relay terminals 30 and 85 shows 12 volts. Terminal 86 show 0.03 volts and terminal 87 show zero volts.

There is no voltage at either of the fuel pump terminals.

The readings at the relay is counter to to what Haynes states (86 should read 12 and 85 should be ground).

I not sure where to check next, really do not want to pull the tank. Any assistance would be appreciated.

Thanks,
Dan

[Cap'n Krusty]

Hi All,
Need a little help to diagnose a fuel pump problem in a 75, I do not hear the pump when I turn the key to the run position.

The car was running, I had a few occasions where it would not start, let it sit for a few days and it was start right up.

The grounds: under the relay board, battery and transmission have all been cleaned.

All fuses are good.

The relay is working as I can hear it click into position.

When the key is in the run position relay terminals 30 and 85 shows 12 volts. Terminal 86 show 0.03 volts and terminal 87 show zero volts.

There is no voltage at either of the fuel pump terminals.

The readings at the relay is counter to to what Haynes states (86 should read 12 and 85 should be ground).

I not sure where to check next, really do not want to pull the tank. Any assistance would be appreciated.

Thanks,
Dan

You don't have to pull the tank to access the pump on a '75. The Cap'n

[solex]

Cap'n I know this I checked the connections at the pump, I thought that there may be a ground that I may be missing. Any ideas?

[Katmanken]

One of the two wires connected to the pump is the ground. It should be brown and can be tested for connection to the chassis ground with a VOM.

If your hot wire to the pump isn't energizing, then trace that one back for problems. Also check it for a ground connection in case it's shorted.

D-jet (2.0 manifold pressure type) or L-jet (1.8 air flap) EFI?

[solex]

One of the two wires connected to the pump is the ground. It should be brown and can be tested for connection to the chassis ground with a VOM.

If your hot wire to the pump isn't energizing, then trace that one back for problems. Also check it for a ground connection in case it's shorted.

D-jet (2.0 manifold pressure type) or L-jet (1.8 air flap) EFI?

Thanks, how do I trace the wire without removing the tank? Also I have D-Jet 2.0L

[black73]

I have had problems with bad connections at the fuse on the relay board. Even though the fuse was good and the connection checked out ok with the VOM. I finally figured out I was making the connection good when I pressed on both ends of the fuse with the probes. Pulled the fuse out and squeezed the connectors closer together to make the fuse fit tighter...problem solved. Good luck!

[underthetire]

I've had problems with the relay not fitting in the socket very well. I used WD40 and spread the pins on the relay and put it in and out a few times to work the wd40 so the tarnish goes away. No problems since.

[Katmanken]

Most VOM's have a continuity checker that beeps when both VOM leads are shorted together. Turn the VOM to continuity, contact the brown wire going to the pump with one lead, and touch a bare part of the chassis. If it's grounded, it will beep or buzz

Try the same check on the other wire to the pump. If it buzzes too, there is your problem wire.

You are going to have to trace the wiring from the pump to the dash. I have 2 1974's and no front pump wiring on the harnesses. But since I swapped harnesses, there is a part of my harness that extends from the fusebox area into the front trunk area. Some of it goes to the right to connect to the sender on the top of the fuel tank, the wipers, and the blower box. I'd look around there for wires to the pump or maybe on the left side of the depression that holds the fuel tank.

Note the wire color(s) and size on the pump wires and look for a match. Brown is always ground. Have a circuit diagram for a 1975? It should show where the pump wires attach.

[Mike Bellis]

30 is power from tha battery
85 is pump on power from the ECU
86 is ground
87 is power out to the pump.

Put a jumper wire from 30 to 87. You should hear the pump. The pump wires should have power. Your relay may "click" and still be bad.

[914_teener]

30 is power from tha battery
85 is pump on power from the ECU
86 is ground
87 is power out to the pump.

Put a jumper wire from 30 to 87. You should hear the pump. The pump wires should have power. Your relay may "click" and still be bad.

I had a crack in the hot wire next to the pump about 2 inches back of the connector. Inspect it well before you start tearing things apart.....how do I know this?

Also spreading the relay pins and contact cleaner also is a great idea. How do I know this too?

Good luck.

[solex]

Gentlemen,
Thank you for the suggestions, I will get back to you with the test results.

Regards,
Dan

[mikea100]

I’ve had problem with the relay top plate stuck open (1976 2.0 – same setup as yours). Remove black cap from the relay (leave relay plugged in), with keys in “On” position press on top plate, you should hear fuel pump buzzing for 1 sec. I think that this top plate is electromagnetic and there’s a little spring on the side that pulls it down. Sometimes it gets stuck. Hope this helps, good luck.

[ericread]

I had a similar problem a few months ago. Rather than using a shotgun approach, I used pbanders worksheets to systematically check the system:

http://members.rennlist.com/pbanders/FPChecklist.htm

My suggestion is to follow this process. It worked for me.

Eric Read

[914_teener]

I had a similar problem a few months ago. Rather than using a shotgun approach, I used pbanders worksheets to systematically check the system:

http://members.rennlist.com/pbanders/FPChecklist.htm

My suggestion is to follow this process. It worked for me.

Eric Read

(IMG:style_emoticons/default/agree.gif)

I got to Brads list after I had torn even the ECU harness out. Went to his flow chart is how I found the bad wire at the pump.

[solex]

Guys thank you for the pbanders post. I diagnosed a problem with the relay board (went through the procedure 3 times to verify)

I have the board out and will begin the rebuild process. Attached are a few pictures of it's current state.

Regards,
Dan

[solex]

BTW, what is the best way to clean the tar off of the relay board?

[914_teener]

BTW, what is the best way to clean the tar off of the relay board?

Oh man your terminals are in rough shape. Your time might be better spent trying to find a better one.... or one that is already rebuilt. It' is a time consuming chore, and then to resolder those rivets to the traces (IMG:style_emoticons/default/smash.gif) ...they need to be REALLY clean.

Short answer is lots of patience and the pick tool set from harbor frieght is what I've used.

[76-914]

BTW, what is the best way to clean the tar off of the relay board?

I'm sure someone will trump this but I left mine i the sun awhile then gently pried the backing out, in pieces, with a screwdriver. The thimbles or brads seem to be a common trouble spot. Rather than trying to com press the thimbles, I cleaned ad soldered them. After repairs were made I filled the back with a tube of black silicone. That was a year ago and it's still working.

[solex]

Hi, I finally got around to getting another board and connector for the main harness.

Cleaned everything up checked all traces from the top side of the board and installed the connector and still no fuel pump.

I went through PBANDERS check again and have one question in the problem isolation area. At the point where I'm check pin 87 on relay 74 and I turn off the key I do not get exactly 0 volts (around .4 to .2 volts) does the indicate that I should check the power to the relay board?

[76-914]

Isn't there always some voltage to the relay board i.e. fuel pump relay?? Seems to me I read that here recently.