bad fuel pump?

[Bologna Hammer]

I have a 95 Yukon with 5.7l TBI I recently got with 240k miles. good shape but needed some maintenance. I replaced plugs and wires, fuel filter driveline fluids and its been running decent for the most part. however sometimes when Im driving and let off the accelerator it surges down before leveling out or getting back into the accelerator. now go to start it in the morning to get to work it just cranks, wont try to fire all or even sputter, turn the key to on position and cant hear the fuel pump prime so I got a fuel pump to put in this weekend. would the surging be a symptom of a fuel pump going bad before just crapping out? other common problems with these that could be the culprit? just looking for someone with more experience on these

 

[OR VietVet]

Before replacing any pump I would want to get a fuel pressure reading, KOEO, at least and see if holds pressure when shut off. If it will not start, is it a fuel problem or is it a spark problem? Did you check? Also, depending on where you are at and the rust, and depending on mechanical background, you may be in for a treat trying to swap out the fuel pump. That surging may be related to the TBI spiders or an ignition module or or or or....etc.

The reason I say some of this is that you did no tests except for the KOEO and listen for pump and therefore I am worried of the mechanical knowledge and ability. If I am wrong, I apologize.

 

[wsteele]

What a bunch of boloney! Sorry, I couldn't resist.

I agree with @PNW VietVet, you need to check the fuel pressure with a gauge. Most FLAPS will loan or rent you a pressure gauge (don't pay a lot for a rental as you can buy a quality one for like $25 on Amazon). With key off, drain the residual pressure, screw it onto the Schader valve on the fuel rail, turn the key on (not start) see what the pressure reads. Turn the key off and see if the pressure declines or stays primed. If it bleeds off or you don't have sufficient pressure after key on, you know it is likely the pump or pressure regulator.

Check the pressure regulator also, to make sure it isn't leaking. The surge could be gas being pulled into the intake through the vacuum line on the regulator when you let off the gas.

 

[Bologna Hammer]

Before replacing any pump I would want to get a fuel pressure reading, KOEO, at least and see if holds pressure when shut off. If it will not start, is it a fuel problem or is it a spark problem? Did you check? Also, depending on where you are at and the rust, and depending on mechanical background, you may be in for a treat trying to swap out the fuel pump. That surging may be related to the TBI spiders or an ignition module or or or or....etc.

The reason I say some of this is that you did no tests except for the KOEO and listen for pump and therefore I am worried of the mechanical knowledge and ability. If I am wrong, I apologize.

I get it. I do a bit of DIY but almost all my experience is with tuner cars. the reason Im at this point is generally KOEO you should hear the pump prime and Ive heard fuel pumps are common on these. along with the ignition module. I can swap parts all day long just the diag I have trouble with.

What a bunch of boloney! Sorry, I couldn't resist.

I agree with @PNW VietVet, you need to check the fuel pressure with a gauge. Most FLAPS will loan or rent you a pressure gauge (don't pay a lot for a rental as you can buy a quality one for like $25 on Amazon). With key off, drain the residual pressure, screw it onto the Schader valve on the fuel rail, turn the key on (not start) see what the pressure reads. Turn the key off and see if the pressure declines or stays primed. If it bleeds off or you don't have sufficient pressure after key on, you know it is likely the pump or pressure regulator.

Check the pressure regulator also, to make sure it isn't leaking. The surge could be gas being pulled into the intake through the vacuum line on the regulator when you let off the gas.

I was going to check the fuel pressure but I couldnt see the fuel rail. it looks like 2 fuel lines come off the back of the throttle body and run back behind the engine. I havent had a chance to spend much time checking it out.

I figure for as cheap as I can get a fuel pump and in 240k miles I dont think it has been replaced cheap insurance IMO

 

[OR VietVet]

To check the fuel pressure on that rig you will need to get a fuel pressure tester that has the adaptor to attach inline with the fuel feed line at the back of the TBI. You have to unthread the line and attach the adaptor to the TBI and then the other end of the adaptor to the hose you removed from the TBI.

 

[Bologna Hammer]

To check the fuel pressure on that rig you will need to get a fuel pressure tester that has the adaptor to attach inline with the fuel feed line at the back of the TBI. You have to unthread the line and attach the adaptor to the TBI and then the other end of the adaptor to the hose you removed from the TBI.

thats what I thought. I tried to break that line loose cause the lines were a pain in the ass when I did my fuel filter. I should get the same results if I tap in where the fuel filter is right? since those lines were recently broken loose.

 

[OR VietVet]

If there is an adaptor that fits on the engine side of the filter, I don't see why that would not work.

 

[Bologna Hammer]

little more info on it since I was able poke at it on break. I used a test light on the connectors in the TB and when cranking it will pulse so that should rule out the ignition module I believe. then it would be between wiring to the pump or fuel delivery to the TB

 

[exp500]

Test fuel pump output by disconnecting fuel filter and pump in bucket. Min 5 GPH. If you have that and spark put in a fuel pressure regulator Kit in TB.

 

[Bologna Hammer]

got the fuel pump changed out and fired right up, runs good now but still surges a couple times after letting off the accelerator so on to that endeavour. I havent checked for any vacuum leaks though Id think that would be more consistent.