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914World.com _ 914World Garage _ Fuel Pump Issue

Posted by: dralf May 21 2019, 01:55 PM

Foe the past few weeks I have been replacing components in an effort to resolve my intermittent running issue. Today after my last cleaning and securing many electric connections I tried to start my 75 D jet baby. Much to my disappointment it did not start. I soon realized I did not hear the fuel pump run as I turned the key. I replaced what I think is that relay (red in my picture) for with a meter I saw the pump was not getting any power. The new relay did not fix the problem although I though I heard some noise as I fumbled trying to get the relay pins in the correct slots. I thought I would check the pump for good measure and ran 12 volts to it directly and it did not run. So it appears that not only am I not getting power to the pump but the pump will not run also. My question now is how do I check to see if the relay board actually has power to the relay slots ( which holes do what ) and then why does the pump not work being hot wired. I only ran a positive wire to it, for it looks like the ground is always on. Does the pump not run if it reaches pressure. Just an added note, as part of my repairs I replaced my ignition wire harness with one from Bowlsby. Any help in my trouble shooting is appreciated.

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Posted by: lierofox May 21 2019, 03:42 PM

In the engine bay I'd check:

+12v Battery power to the relay. <-If missing, possibly bad 25a fuse or bad connection
+12v power to the relay coil. <- If missing, no signal from key switch when starting
Ground at the relay coil.
+12v power leaving the relay. <-If missing, could be bad relay contacts

At the fuel pump I'd check:
+12v power at the fuel pump.
Ground at the fuel pump.

Funnily enough (since you mentioned Bowlsby's wiring harness) I found this: http://bowlsby.net/914/Classic/zTN_FI_FPChecklist2.pdf

If that all checks out your fuel pump might be bad and getting a bad spot on the brushes.

Posted by: cary May 22 2019, 07:21 AM

The relay to the right of that is the D Jet power supply relay. The fuel pump relay get its switched power from that relay.

Posted by: cary May 22 2019, 07:35 AM

Going from memory. Standing above the relay board.

Posted by: mtndawg May 22 2019, 07:55 AM

I just went this testing process last week. Test the slot (orange arrow) for 12v with the key on as indicated above. If that’s working it means you are getting signal from the power relay. If not you’ll have to check the power relay. I would also check for continuity from the ground pin hole to the body on the fuel pump relay plug that is also shown in the photo.

Just read the original post again. The pump has a hot wire and ground so if you only ran a hot wire to the pump it wouldn’t run. I believe the original plug has two slots for hot and ground. They would both need to be connected to run the pump to test it.