hi my name is tom. 1991 ford f150 xlt 5.0L efi wont start ok well it will start on prime only have 40 psi fuel presure have replaced pickup, fuel presure reg. model on distributor, tps, bypassed front tank never got used so hooked up rear tank only getting pulse but wont start unless you prime it

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First off, welcome to FTZ!
Second, find and by-pass with a jumper wire, the safety fuel shut-off inertia switch............I believe it's under the pass. side kick panel on 87-91s.
Try that for starters.

 

It runs on prime but wont stay running yes injectors are firing to.

 

NEVER bypass an inertia switch. It is put there to stop the fuel pump from pumping fuel in case of an accedent.

Dave, the EFI systems go, 85-89, 90-91, and 92-96

The check valve on this system only keeps the returning fuel from going back into the wrong tank, and is in the FDM ( fuel delivery module)
There was a recall (that timed out) that installed an external checkvalve on the fuel line,But those are rare

My guess is that he has a corroded relay, or a bad relay harness connection

He already stated his other tank has a bad pump

I would
1 have someone listen by the gas fill when I first turn on the key to verify the pump is running
2 if the pump did not cycle, take the relay out of the harness, and test with a test light

Keep in mind, you will have to keep cycling the key, as the circuit only will be hot for 1 second.

This is my last post here. I am still pissed about KW saying my home is a junk yard, and he has never been here to see it.
How can he judge me?

Just because I choose to have several cars, this makes me live in a junk yard?
What about Jay Leno? He has over 200 cars.

 

Tanks lol

 

KW said what?

 

"Never bypass an inertia switch"....................it's quite acceptable as a testing procedure.
You wouldn't believe how many I've seen fail.

 

You edited your post
Gotta love the mods here. They are just like the ones at the other place

 

Even me Charlie? Really?