FergusonT

The other day I go out to start the truck, it turns over but wont start. Sometimes when I try to start it, it sounds like it runs for a second before it cuts out.

I go get a fuel pressure gauge, key on/engine off it was around 52psi. Just out of curiosity I replace the fuel filter. Now I'm down to around 20psi. I can hear the fuel pump just fine. The pressure is actually up around 58psi while the pump is running but immediately drops once the pump cuts off.

I am confident in my repair abilities, but diagnosing problems is not my strongest point.

tech2

fuel pressure leakdown is what your describing. It can be external and you would smell fuel and maybe even see a leak.

If its internal, it could leak:
-past the injectors into the cylinders,
-past the regulator into the return line back to the tank
-through a ruptured regulator diaphram into the crankcase
-back through the feed line because of a bad check valve.

If its the check valve, typically you would have a long crank time after it sits overnight.

If its injectors, there might be a hard start issue when re-starting a warm engine.

If its the diaphram, there would be fuel in the regulator vacuum line.

FergusonT

Im not able to start it at all, it just cranks. I don't see or smell fuel anywhere along the fuel lines back to the tank. Im not getting any fuel in the vacuum line, sounds like it could be a check valve. I was about to go clamp down the return line and see what the pressure does then.

FergusonT

So which line is the fuel return. there are 2 identical lines coming off the fuel rail..

tech2

the return is out of the regulator end of the fuel rail.

So it will go INTO the fuel rail, to all the injectors. At the end of the rail is the regulator and exit to the outlet line back to the tank.


don't clamp on any plastic fuel lines.


you could try a clear flood mode start or pull a plug to see if it fuel saturated

FergusonT

Ok, so I figured it out...I was looking last night and it was dark, couldnt see where anything went. Pinched it off and primed the pump until I was at the right pressure, then primed it again to see if it would go further, it pretty much stayed the same pressure. It started right up. I let it run for a few minutes, watching the pressure stay around 48-50 psi. Shut it off, let it sit for a minute, then it started back up, with low pressure still 48-50

FergusonT

With the truck running and the vac line pulled off the regulator im at a consistent 58psi

67Motorcat

Time for a new fuel pump.
If it's the original it is showing the classic signs.....they just plain get wore out around after 125K miles or so.

FergusonT

Prolly fuel pump

Clamped off return line/pulled vac hose off regulator, got 90 psi

Replaced regulator

Key on engine off 52psi still.....engine running around the same, pull vac hose off while running, jumps up to around 58-60psi....so basically the same results after replacing the regulator

FergusonT

So who can tell me which fuel pump I need to get? Looks like there are 3 different AC Delco pumps.