Jumping 12V to B+ to Test Fuel Pump? (2 Viewers)

[wopwophuey]

1994 80 Series, right hand drive, gas.

I am trying to see if the fuel pump is bad or if the fuel pump relay is bad. I see recommendations to Jump 12V to the #3 terminal in fuel pump relay to directly power the sensor (Emergency Troubleshooting Procedures - FAQ Item (Recommend Keeping Copy in Truck) - https://forum.ih8mud.com/threads/emergency-troubleshooting-procedures-faq-item-recommend-keeping-copy-in-truck.115816/) - what kind of wire should i use to do this? Do i just take a wire and hold it to the positive terminal on the battery and push it the other end into the #3 terminal?

For context, this puppy hasn’t run in 18 months or so. When I put it into the garage for storage, I had run most of the gas out of the tank and left ~.5 - 1 gallon in the tank. I put 1.5 gallons in today. Cranks, but won’t start. I was able to start it up by spraying starter fluid into the intake, so I know I’ve got spark and hopeful i have compression. Fuel pump doesn’t sound like it’s running and the fuel gauge shows completely dry. Also, the speedometer doesn’t (or didn’t work 18 months ago), but I don’t know if it’s related. Any advice is greatly appreciated!

 

[CharlieS]

You can bypass in the diagnostic connector with a basic jumper.

Recently shared by @jonheld:
By jumping FP-B+ in the diagnostic connector you have bypassed all fuel pump logic and the pump will run whenever the key is in the ON/RUN position. This is potentially dangerous as the pump will continue to run in the event of a collision.

I marked my diagnostic connector with a paint pen so I can easily jump the fuel pump as a limp home measure to get off trail.

 

[wopwophuey]

You can bypass in the diagnostic connector with a basic jumper.

Recently shared by @jonheld:
By jumping FP-B+ in the diagnostic connector you have bypassed all fuel pump logic and the pump will run whenever the key is in the ON/RUN position. This is potentially dangerous as the pump will continue to run in the event of a collision.

I marked my diagnostic connector with a paint pen so I can easily jump the fuel pump as a limp home measure to get off trail.

Thanks for the reply! Just to be clear, like basic jumper cables? I’ve never done anything electrical with a car, so I’m fumbling my way through it.

 

[CharlieS]

I have a simple jumper wire, like 12 guage wire, with flat pins on the end that I made, but some guys even use a paperclip. Jumping the battery 12v + (+B) and Fuel Pump (Fp) pins in the diagnostic connector on the firewall forces the fuel pump to run on high, bypassing the fuel pump relay.

 

[CharlieS]

Here is what I made for this:

But you can literally use a paperclip (not plastic coated, of course).

 

[sjpitts]

Clarification request-- this is for the 93/94 OBD 1 vehicles? And it uses the 93/94 diagnostic port?

I guess I should go find the @jonheld post.

 

[CharlieS]

Mine is a 1994 US Delivery 80 Series with OBDI and this procedure works on mine.

 

[jonheld]

Clarification request-- this is for the 93/94 OBD 1 vehicles? And it uses the 93/94 diagnostic port?

I guess I should go find the @jonheld post.

This is only for OBD1. There are 2 different diagnostic connectors between the 91/92 FJ80 and the 93-early 95 FZJ80, but the concept is the same.
By jumping B+ to FP, you are providing +12 directly to the fuel pump when the key is in the ON/RUN position, bypassing all fuel pump logic.

91/92 FJ80

93-95 FZJ80

 

[sjpitts]

Thanks much Jon--

So is the electrical connection in doing this good enough to get you home, or is this something that should really only be used for testing purposes?

 

[jonheld]

Thanks much Jon--

So is the electrical connection in doing this good enough to get you home, or is this something that should really only be used for testing purposes?

It will keep the fuel pump running as long as the key is in the ON position and the EFI relay remains closed.
In the event of a collision, rollover, etc., the fuel pump will continue to run even if the engine stalls. You need to be aware of the potential hazard if you decide to drive in this condition.