Stumped! No power to fuel pump

[Stormranger]

I've searched and I can't seem to find an answer, I have no power to fuel pump or inertia switch, but there is power at relay and relay is good, with the key on the "on" position there is no check engine light. What should I do! 1993 4.0 5 spd 2wd

 

[SenorNoob]

If you actually have power AT THE RIGHT PINS of the relay and no power at the inertia switch then the wire between the 2 is broken.

 

[Stormranger]

I just rechecked at the relay there is power to the left pin and the center top but not the right one, whAt is my next check? I'm missn work today because of this

 

[jrpdash9]

So on a 88 b2 I had the relay would work for 10 min and turn off. I Eventually tore the relay apart and stuck a tooth pick in it to keep it closed so I could get it to the parts store. Maybe try over riding the relay just to be sure?

 

[RonD]

Power for fuel pump:
Battery---Fuel pump fuse-------fuel pump relay--------inertia switch------fuel pump

The fuel pump fuse supplies 12v to the relay all the time, so one of the relay contacts should have 12v all the time, key on/off doesn't matter, this is the power for the fuel pump, and is sent to the inertia switch when relay closes.
So if you have no 12v at the relay with key off then fuse or wire to fuse is the issue.

A second contact in the relay will have 12v only when key is on, this 12v comes from the EEC relay, it doesn't power the fuel pump, it is power for the relay only.
The PCM(computer) grounds the relay to close it and send power from the fuel pump fuse to the inertia switch/fuel pump.
So the relay has 12v when key is on but no ground, so stays open, PCM grounds it for only 2 seconds when key is first turned on(this primes the system), then grounds it off and on as needed by the running engine.

So you will not have power at the inertia switch all the time, you will only have power when PCM has "turned on" the fuel pump relay.

 

[samx227]

Just my 2 cents. Check ecu fuse (30a in pwr dist box ), and check your eec IV relay, next to fuel relay.

 

[adsm08]

Find the diagnostic connector, and find the blue and orange wire. If you look down at it with the narrow end as the "top" I think it is the top right pin is the one you want. I am more sure of the color than the position.

If you know you have power into the relay what you need to do is check continuity to ground from that wire as the key is turned on. You should get a momentary spike, then read open.

That is the same wire that the computer uses to ground the fuel pump relay. If you don't get ground you may have a wiring problem, or a computer issue and you need to test continuity.

I just had this issue with my 4.0 swap and found that even with a good computer but that line having issues the CEL would not come on.


Also, if the horn works use it to test the other relays. If you can pop each relay into the horn slot and have the horn keep working then your relays are good.