New guy with a fuel problem (I think)

[raposak]

Hey guys, thanks for the opportunity to join the board. Hopefully i will get and give some good info. So here's my dilemma

99 Suburban 2500 with a 454 bogs down bad while under load while giving it some throttle. It has a strong air sucking sound while it does this. I hooked up a fuel pressure gauge and here are the readings.


Truck cold: ignition on truck not running 50psi and drops down to 22 in 5 minutes
Truck cold: Running at 47psi
Truck cold: 2000 rpms at 47psi
Truck hot: 47psi

No matter what rpm when hot or cold, it stays at 47psi. So i'm thinking its either the fuel pump or the pressure regulator. What do you guys think?

[MrShorty]

Assuming the pressure gauge is accurate, it seems pretty certain that the fuel pressure is too low. As you suggest, the next step is to determine if the pump is weak or if the regulator is opening too soon. When I've diagnosed this, I used a C-clamp (or similar) to carefully clamp off the return line from the regulator back to the tank. If this causes the pressure to jump up, then the regulator is likely opening too soon. If this has no effect on the pressure, then the pump is likely too weak (or there is something else like a clogged filter preventing the system from generating sufficient pressure.

[bazar01]

Have you replaced the fuel filter? Clogged fuel filter can cause runnability issues.

In addition to above, pull the vacuum line off the fpr. If fuel comes out of the vacuum line connection at the fpr, it is bad. The fpr diaphragm has ruptured.

Lastly, fuel pump is getting weak.

[raposak]

Fuel filter is 6 months old. I'll try and check the vacuum line, but getting to the actual unit without taking off the intake will be a challenge.

[raposak]

New twist to the problem. I just discovered a puddle of rusty water under the truck coming from the water pump. I looked in the radiator to discover that it is quite low on fluid. So the next question is would low coolant cause the bogging? I was doing some reading on the coolant sensor and the entire engine performance is based on what that little sensor tells it.

[geo1]

I would say youre pressure is low from pump,a good pump will build pressure slowly wwith clogged filter,and not drop that far down in that time span,regulators usually go on the high side.c.t.s needs acurate temp. reading.fill up coolant and see,can anyone say how long that the pump will continue same pressure,hard to say,Id do coolant leak first

[raposak]

ok, got some time to mess with it after changing the water pump, thermostat and coolant sensor. While squeezing the return line, the psi shot up to around 70. The leak off when off before was because of the gauge. I fixed that and it can sit all day with the motor off at 50psi. Running is still at 47. So looks like i'll be swapping out the regulator. Thanks for all the help. I'll let you know how it goes after swapping it out.

- - - Updated - - -

Well that was a big waste of time and money. The truck has the same bogging symptoms. A mechanic friend suggested that the it sounds like my Cats may be clogged. He suggested that I disconnect the exhaust before the Cats and take it for a test drive. My neighbors should love me driving with open headers. Hopefully i'll try that tomorrow.

[geo1]

what the?do you at least have a better reading on fuel presure?47psi was cutting it close

[raposak]

nope, same reading.

[geo1]

i would still check cats,just try a vacuum gauge,should be 20ish at idle when warm,back to f. pump,they will spike higher than 70,hate to say but it think thats still youre problem