Fuel pressure problem


#1

1998 chevy vortec 350. replaced fuel pump(twice),fuel filter, blew air through the lines, replaced fuel pressure regulator. Getting correct voltage at pump. pump runs. still only get 30 lbs of pressure. Need 60. Thought I bought a defective pump took it back. Same result. Doesnt leak anywhere I can find. Pressure doesn’t drop. Just plain don’t get the 60 lbs it requires. New battery as well and new F.P. relay.


#2

Any suggestions?


#3

If you’re not seeing at least 62 PSI of fuel pump pressure, there’s a problem with the fuel pump.

Tester


#4

This is a gasoline engine, right? Maybe draw out the route the gas flows; i.e.;

gas tank > pump > fuel rail > injectors >cylinder
or fuel rail > fuel pressure regulator > gas tank

When you say you only get 30 lbs, you mean you measured it at the fuel rail, right? And you expected to see 60 lbs? Was this at idle then? During cranking? What was the condition you measured?

Seems like the likely causes would be:

  1. pump is not outputting high enough pressure for the volume flow demanded
  2. fuel pressure regulator regulating too low of pressure
  3. injectors are leaking more gas into the cylinder than they should
  4. restriction in fuel line somewhere

Are you able to test the pump pressure separately? i.e disconnect the pump from the fuel rail and just test the pump pressure? Also, is there any evidence the injectors are leaking into the cylinders? Is there a check valve on or near the pump? Has it been replaced?


#5

Wrong parts, defective parts, faulty installation.

I once had a case like this on a suburban from another garage. What it turned out to be was the person was using the fuel hose supped with the airtex brand pump and it was too short. The pump would separate from the hose by sliding off creating an internal leak. Use a proper size new hose and clamp it.

Another time I had one where the fuel pump was grounded through he sending unit. The solder joint at the sending unit return pipe was bad creating a bad connection.

You have checked the power at the fuel pump but have you checked the ground? Backup the ground to a fresh spot on the frame with a new screw.


#6

You state that you have correct voltage at the fuel pump.
Is that static or with the fuel pump running? It could make a difference.


#7

Verify power AND ground directly at the pump

Deadhead the pump . . . measure fuel pressure DIRECTLY at the pump, not at the rail

A good pump should produce roughly double the pressure when deadheaded. So you should see well over 100psi

GM had problems with the fuel pump pigtails melting. Your vehicle was one of the affected models. I’m 100% sure of it. Hopefully your replacement fuel pump had a pigtail as part of the kit . . . some of the cheapo aftermarket kits don’t.

" . . . replaced fuel pressure regulator . . . "

You have CSFI . . . to replace the regulator, you’d need to remove the upper plenum. You didn’t see any cracked or leaking plastic fuel lines in there, you say?