fuel system problem

[MikeG]

OK here's my sad tale. Driving truck home (97 B4000 a.k.a. 4.0L OHV) from inspection (passed), it died at a stop sign and would not start. Suspecting fuel system problems, bought a gage. Zero PSI with key on, and no sound from tank. It was already having a problem not holding pressure after being shut off (had to turn key off and on 3 or 4 times, or crank a while) but otherwise running great.

Although the fuel pump relay clicked, the fuel pump was not making any noise. Jumpered the relay and fuel pump comes on, jumps up to 40psi then zero as soon as jumper removed. Bought a new relay from the 'Zone, same thing. Clicks but doesn't start pump, although jumper does. Checked the inertial switch, wasn't popped up.

So.... is 40 PSI correct at startup? Why would the jumper start the fuel pump, but not the relay? Is there something else that could prevent the fuel pump from starting up? I tried starting it with the jumper on the fuel relay, but no luck. However did not have the gage attached at the time.

thoughts? Tank mostly full, would hate to have to pull it. Guessing the bed would have to come off.

 

[franklin2]

40 psi is close enough to run. Take the relay back out and look carefully at the socket. Make sure the metal tabs in the socket are not bent back or spread open not making good contact. Sometimes you can take needle nose pliers and put a very slight twist to the relay prongs, and then plug it in and see if it makes better contact. Look for corrosion down in there also.

 

[Infamousmazda]

Had the same issue on one a few years back. The plug for the fuel pump right on top. Side tab broke. It shutoff.... Would barely make contact and start. Then sometimes wouldnt start.......maybe something to check out .....

 

[MikeG]

Blown PCM fuse. Should have checked the fuse box first! Darn thing only lasted 23 years..... sheesh.....

Next on the agenda is to figure out why the fuel system isn't holding pressure with truck shut off. Guessing fuel pressure regulator is the most likely culprit. Will post some numbers with my fuel gage.

 

[franklin2]

What you do is pump the fuel system up, and then pinch off the line coming from the tank. If the pressure holds, you know it's the check valve in the fuel pump.

If that doesn't work, then pump the system up again and pinch the return line going back to the tank. If it holds pressure then, you know it's the fuel pressure regulator leaking.

If neither one of those made it hold pressure, then you have one or more injectors leaking. Sometimes you can pump it up and then pull the plugs and some of them will be wet with fuel.

 

[MikeG]

Got it. I've never pulled fuel injectors, so that will be interesting. Also still looking for the fuel pressure regulator - from pictures I've found of engines, it seems like it may be on the back of the driver's side rail, sorta covered up by the coil pack. That sound right?

 

[franklin2]

Does yours look like this? This is supposed to be from a 97 explorer. It will have a vacuum line going to it.

 

[MikeG]

I can't see the back side of it nor much of anything on the driver's side rail. Probably.