Fuel Pump losing power

[Cornerstoneplumber]

I have an 03 Navigator. We got code P0422. Couple weeks later it just didn't start. It cranks but won't start. We have replaced the fuel pump, accessible fuses, and relay.
The fuel pump is getting power, but we discovered it's not getting power when under pressure from trying to start. We traced the power all of the way to the fuse box. The r303 fuse is good, 9or else we would have a fuse box on its way. We tried grounding it to the frame.. and nothing. It won't start and out of ideas.

 

[Cornerstoneplumber]

We changed the fuel filter as well, which was plugged.

 

[Slick Fan]

It could be a bad fuel pump inertia switch. I'm not sure where it's located on your Navigator, but those do go bad from time to time.

 

[Cornerstoneplumber]

Update!

So we learned the problem this whole time has been the infamous non-serviceable R303 is the cabin fuse box. Apparently when you test it, it can NOT hesitate. If it does you need a new fuse box. I've been searching them online and apparently they are very hard to come by... so...

Can you run a bypass to the fuel relay????

We ran one and it starts every time, but to be honest I'm scared to leave it running for more than a few seconds. I can't find anything online about a bypass on this.

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[Cornerstoneplumber]

Thank you! We checked it and it's good. So we went back to the fuse box when we all of the sudden got a computer data error on the dash.

 

[Slick Fan]

Can you run a bypass to the fuel relay????

I don't see why not, just make sure to put a fuse inline that's the same amperage as the one in the fuse box. And of course, make sure that wire cuts the power when you turn off the ignition.