Fuel Pump

[todd8]

Does the fuel pump run at a continuous speed, supplying a constant pressure in the fuel system, or does it speed up and slow down based on the throttle position.

I am under the impression that it runs at a continuous speed, but I am still trying to track down that darn chirping\squeaking noise. I had my wife drive the car while I rode in the back, and the best I can tell, the noise seems loudest from the spare tire well, a little towards the passenger side.

I know that the primary fuel module, with the pump, is on this side of the tank, so I am trying to rule that out as the culprit. NOTE - The chirping noise is only present when the car is in motion above 20 mph, and speeds up and slows down with vehicle speed. If the fuel pump runs at a continuous speed, I would think it would chirp all of the time if it were the source.

2004 Vue 3.5 V6 AWD

[fdryer]

All fuel pumps run at one speed and are rated for far more pressure and volume than needed as a built in reliability factor. The fuel pressure regulator sets the pressure needed and is lower than the maximum pressure generated. So a 95psi pump is regulated for about 50psi for our fuel injection systems. All fuel pumps for EFI system are sitting in the gas tanks that allows fuel to keep the pump cool. It would be very rare for any fuel pump to make noises loud enough for anyone to hear. The small size is designed to run virtually noise free except at ignition ON time before starting. Once the engine runs no one can hear any fuel pump unless an ear is pressed to the gas tank. Its not likely for your pump to be making noise as all inlets are filtered to prevent damage from any large objects that can fit into an inlet line to the pump. A filter sock is the main filter to eliminate crap entering the pump.

Perhaps the rear end noise is from a suspension bushing? Metal on metal rubbing?

[mrtube]

fdryer,

I was able to hear fuel pumps on 1980s-late 90s vehicles that had high pressure pumps, especially if I walked behind the car near the gas tank.

I'm not so sure if this still holds true though, I stopped paying attention at some point.

One thing I am curious about is my 06 grandprix has a returnless fuel pump. Does this runs at one speed with a pressure release in the tank? Or does the pump actually vary speed with demand.

I'm betting the pressure release is in the tank and the pump runs at one speed.

[fdryer]

The specs for 2nd generation Saturns up to '98 do not mention anything about a returnless fuel system so I presume they're using a return line from the fuel rail. 3rd gen Saturns (S-series) have their fuel system returnless; the fuel feed to the fuel rail is one way with no return while the fuel filter does have a return line for excess fuel back to the tank. Single speed fuel pump. Picture below; 1-inlet, 2-return, 3-outlet to fuel rail.

Saturn models from '99 up use a return line from the fuel pressure regulator near the fuel rail. I believe this is to control pressures better while incorporating vacuum on the regulator to lower fuel pressure while idling since it isn't needed. As manifold vacuum changes (decreases) during acceleration and cruise, fuel pressures rise to accomodate the higher demands of the injection system. When vacuum drops to zero, spring pressure controls fuel pressure. This spring is preset at the factory and no adjustment is required. By varying fuel pressure according to engine vacuum, a constant pressure differential across the fuel injector opening is maintained. My '03 L300 specs; @ignition ON - 55psi, and I presume this increases some as power is used.

I haven't checked every model so I'm presuming quite a bit. Since every GM car cycles the pump at ignition ON time for 2-3 seconds then shuts off if no cps signals are detected, this minimizes over pressurization and flexing of soft fuel lines. When the engine is detected to be running over 400rpm the fuel pump is turned on. This serves two purposes; SAFETY as well as modulating fuel pressures when there's a demand.

I'm not sure why some GM cars fuel pumps are loud.

[mrtube]

Fdryer,

My 06 grandprix doesn't have a fuel filter. I have no idea what type of system our 06 vue has? Is it returnless?

[fdryer]

I don't have the manual for '06 but do for '05 and presume they're the same? Vues are using a returnless system. Below is a brief pdf from the '05 manual.

I don't have the manual for the '06 Grand Prix but do for '05; The fuel rail (1) is mounted to the lower portion of the intake manifold and distributes fuel to the individual fuel injectors (3). Fuel is delivered to the fuel inlet tube of the fuel rail by the fuel pipes. The fuel then goes through the fuel rail to the fuel pressure regulator (2). The fuel pressure regulator maintains a constant fuel pressure at the fuel injectors. Remaining fuel is then returned to the fuel tank.

[1saxman]

'speeds up and slows down with vehicle speed'

Most likely in the driveline/wheels area, probably the rear brakes. Also might be a U-joint or carrier bearing in the rear driveshaft. Maybe a CV joint in a rear axle. I would suspect the brakes first, including the parking brake which may not be releasing all the way when the lever is lowered.

[mrtube]

Walked behind my 06 grandprix tonight with it running and heard the distinct fuel pump sound.

I think all of the high pressure fuel pumps have a sound.

[MoparNut]

If it's AWD, my guess is the rear axle seals-spray a few shots of silicone or synthetic spray grease in there and drive it to see if it temporarily goes away. Very common problem on VUEs. Also, don't overlook the liftgate interior trim panel clips popping out partway and squeaking, but this generally presents only over bumps.

[todd8]

If it is the axle seals, how hard are they to replace? This noise starts up after about 20 minutes of driving. On short trips it is not present.

I did change the old differential fluid to Royal Purple Synchromax - do you think that could be the problem?

[MoparNut]

Serious PITA...have to remove lower control arms, coil springs, etc. to get the axle shafts out. Not worth it, if you ask me, but go for it if it is definitely the cause and you feel adventerous. Fluid shouldn't be a factor.

[MoparNut]

adventurous* oops