Hi all !
1993 W250 5.9L Magnum.
Was running rough, stumbles at idle, dogs out/back fires with any throttle. New I had a burnt plug wire.
Did plugs, wire cap rotor. No improvement.
Was messing with timing and decided to squirt a little gas into
throttle plates and the engine smoothed right out.
Couldn't hear the fuel pump come on plus the filter is on the pump
in the tank, so I put a new pump and filter in. No improvement.
I had fuel at the shrader valve on the rail. Went to Rock Auto under fuel and they listed a Fuel pressure regulator. There isn't one on this truck at the rail, Only SS braided line from hard line on frame to fuel rail. I disconnected it and had a piece of clear hose same diameter as male line inserted in to SS quick connect and turned on key. Plenty of fuel volume for 2 secs until the relay shuts it off.
Put a guage on line and cycled the pump a couple times with key and could only get ~10 psi. During my troubleshoot I suspected voltage to pump, Ran a meter on line in and with truck running had 14.0 V.
Cleaned all grounds.
1) What should the Psi be ? ~ 40psi?
2) Should I measure psi at Shrader vale on rail?(dont' have an adapter)Can I pull valve out like a tire shrader vale and plumb to guage?
3) Could it be plugged injector(s) ? Should I replace all of them?

Any advice appreciated !

Pressure should 40 psi at 2000rpm. Did you install an airtex pump? There have been a number of failures of the brand. Pressure regulator is part of the pump on your truck I think.

Yes, Psi regulator is part of pump
Bought the pump thru Napa, don't remember brand.
Put a guage on port exiting pump and had 18 psi
Had 14 volts on pump while running yesterday.
Should I unplug it and hot wire 12v and ground
and restest?

Can't believe old pump and new pump are the issue.
But I swear I remember hearing the pump pressure up when
key was on before the issue, now I don't hear it.

Thanks Stumpy !

Sounds like a bad pump. Lowering the voltage isn't going to make it pump more pressure.

My point was to hot wire it directly off the Battery directly with +12V and with battery ground to eliminate a short.
(had 14v with truck running)


Thanks

Just came in from shop
Old pump puts out 40 psi on the Bench
Jumped the new pump in the tank and had 50psi.
So even though I had 14v, I'm missing some amps.
I'm guessing ground, I cleaned all terminals in relay
that could be it too)
Least I know its electrical.


Option 1. Run new ground and retest thru relay
Option 2 If No go, run new 12V wire from relay
Option 3 it's bad contacts in relay

Anything I missed?

Thanks !

Fuel pump relay?

Robert

92-93 magnums had the regulator on the fuel rail. In 94, they went to single line feed with the regulator in the fuel pump module.

I thought the filters were on the frame still on the 93's? that would be the first thing i'd change.

Started with a fuel pump relay, wouldn't plug in....back to Napa.

No Fuel psi regulator on rail.
Will update when I have fixed, by the wkend.

Appreciate the replys !

It was the ground. Siamesed splice right at pump plug then to Body.

New pump has 50 psi.

Thank you !