Hesitating to Start

[diezelraccoon]

Still seeking answers on this with my 03 Tahoe with the 5.3 engine. I noticed at about 1/4 a tank if it’s sitting all day/nignt you go to start it and it takes a little longer for it to fire up. There’s been times the gas light was on and I was parked at an include downhill and it would not start and I had to put it neutral and let it roll to a flat surface for it to start. I’ve noticed now when it’s down to 1/4th a tank on level surface after sitting all night it does the same thing.
I do believe if I turned the key to the on position and let the fuel pump run for a few seconds before starting, it will fire up. The fuel pressure was below specs that I outlined in a previous post. I’ve already placed the fuel pump with an OEM. Still trying to figure out what’s causing this. Perhaps fuel filter or fuel pressure regulator?
Below is a link to a video of what it’s doing.

Watch unnamed | Streamable

Watch "unnamed" on Streamable.

streamable.com

 

[swathdiver]

I cannot view the video, says private. Anyway, I think the pump is losing it's prime because of a leak, the system isn't sealed anymore.

My first look would be the pump but you said that that has been replaced. Did you replace the entire unit with the sensors and sender and such or just the pump? Did you triple check the lines for leakage?

 

[diezelraccoon]

I cannot view the video, says private. Anyway, I think the pump is losing it's prime because of a leak, the system isn't sealed anymore.

My first look would be the pump but you said that that has been replaced. Did you replace the entire unit with the sensors and sender and such or just the pump? Did you triple check the lines for leakage?

I replaced the entire unit. As far as I could see there were no leaks.

 

[rockola1971]

I replaced the entire unit. As far as I could see there were no leaks.

Did you use aftermarket or OEM pump module? If your pressure is out of spec then its either the regulator, pump or less likely filter. You should replace sock and inline filter always when installing a new pump. I would put a new regulator on at this time also.

 

[justirv]

I replaced the entire unit. As far as I could see there were no leaks.

I had a similar issue with my '02 Z71. I had replaced the internal tank fuel pump as well. You state your replacement was OEM, where was it purchased? I had to replace my "new" OEM to correct the problem. As @swathdiver stated, it sounds like you are loosing prime. Replacing the fuel filter is always a good idea when servicing the fuel system. I would put a pressure gauge on the fuel rail, and monitor initial pressure when key is "on", and watch the leakdown over time. Check the pressure spec for your rig, as gas and flex are different.

 

[strutaeng]

I was able to view the video. It took "a little" longer to crank, but not that bad honestly.

Your next step would be to check fuel pressure with a gauge. It could be the pump, but could also be the FPR.

 

[diezelraccoon]

Did you use aftermarket or OEM pump module? If your pressure is out of spec then its either the regulator, pump or less likely filter. You should replace sock and inline filter always when installing a new pump. I would put a new regulator on at this time also.

It was an OEM/ACdelco fuel pump sending unit, the entire thing. This problem is occurring with the old fuel pump so it can’t be the fuel pump.

 

[rockola1971]

It was an OEM/ACdelco fuel pump sending unit, the entire thing. This problem is occurring with the old fuel pump so it can’t be the fuel pump.

Unless your new fuel pump is bad too.

 

[diezelraccoon]

I had a similar issue with my '02 Z71. I had replaced the internal tank fuel pump as well. You state your replacement was OEM, where was it purchased? I had to replace my "new" OEM to correct the problem. As @swathdiver stated, it sounds like you are loosing prime. Replacing the fuel filter is always a good idea when servicing the fuel system. I would put a pressure gauge on the fuel rail, and monitor initial pressure when key is "on", and watch the leakdown over time. Check the pressure spec for your rig, as gas and flex are different.

At the time I bought it off Amazon, but I stopped buying OEM parts from Amazon. I’m confident it’s not the fuel pump because this issue was occurring before I replaced it. The fuel pressure specs are as follows before I replaced the fuel pump.

46 psi when key was on but engine off.
42 psi with engine running
42 psi after engine was ofF

 

[diezelraccoon]

I was able to view the video. It took "a little" longer to crank, but not that bad honestly.

Your next step would be to check fuel pressure with a gauge. It could be the pump, but could also be the FPR.

These were the fuel pressure readings before I replace the fuel pump.

46 psi when key was on but engine off.
42 psi with engine running
42 psi after engine was off

 

[justirv]

At the time I bought it off Amazon, but I stopped buying OEM parts from Amazon. I’m confident it’s not the fuel pump because this issue was occurring before I replaced it. The fuel pressure specs are as follows before I replaced the fuel pump.

46 psi when key was on but engine off.
42 psi with engine running
42 psi after engine was ofF

I agree with you on re: AMZ "oem" parts, I quit ordering those from them several years ago. Your fuel pressure sounds low to me, I do not recall actual spec (maybe 58psi?), with a bit of difference between gas and flex. Check the fuel pressure regulator on the rail? That bleeding off pressure could also affect your hard starts.

 

[Fless]

It would be helpful if there was some vehicle and drivetrain info in your signature. Not all are the same.

For fuel pressure, according to Haynes:
KOEO
Flex Fuel: 48-54 psi
Non-Flex: 55-62 psi

Either way the KOEO pressure is below the minimum. If it's a FF system has the inline fuel filter been changed?

 

[nonickatall]

These were the fuel pressure readings before I replace the fuel pump.

46 psi when key was on but engine off.
42 psi with engine running
42 psi after engine was off

Isn't that a little low? Should be between 55-62 PSI, so you should swap the fuel pressure regulator and fuel filter, if your Tahoe has one. Some of the cars have the fuel filter inside the fuel pump.

 

[diezelraccoon]

Isn't that a little low? Should be between 55-62 PSI, so you should swap the fuel pressure regulator and fuel filter, if your Tahoe has one. Some of the cars have the fuel filter inside the fuel pump.

Well since I relaxed the entire fuel pump assembly that takes care of fuel filter if it was on it, but I believe mine is elsewhere.
I will try replacing that and fuel pressure regulator.

 

[diezelraccoon]

It would be helpful if there was some vehicle and drivetrain info in your signature. Not all are the same.

For fuel pressure, according to Haynes:
KOEO
Flex Fuel: 48-54 psi
Non-Flex: 55-62 psi

Either way the KOEO pressure is below the minimum. If it's a FF system has the inline fuel filter been changed?

Not to my knowledge but I will replace it along with fuel pressure regulator

 

[Fless]

FYI the FPR has no effect on the fuel pressure when running KOEO tests. On your system it works using supplied manifold vacuum, which is nonexistent when the engine isn't running.

 

[diezelraccoon]

FYI the FPR has no effect on the fuel pressure when running KOEO tests. On your system it works using supplied manifold vacuum, which is nonexistent when the engine isn't running.

Where do you suggest I go from here since I’ve already replaced the fuel pump?

 

[strutaeng]

FYI the FPR has no effect on the fuel pressure when running KOEO tests. On your system it works using supplied manifold vacuum, which is nonexistent when the engine isn't running.

I didn't know this. I thought it was possible for a faulty FPR to send excess fuel back to the tank, causing a low fuel system pressure. Something about the spring inside the FPR diaphragm getting weak or something like that?

OP, you can try capping the return fuel line temporarily. I use vacuum caps and one of those fuel line hose clamps. Prime the system and this is what your fuel pump is able to produce at maximum pressure.

When I was doing troubleshooting on my 99 Silverado I recall my pump maxed out at 100 psi. That truck still has the original fuel pump and it's at 260k-ish. I've only done that once.

 

[Fless]

I didn't know this. I thought it was possible for a faulty FPR to send excess fuel back to the tank, causing a low fuel system pressure. Something about the spring inside the FPR diaphragm getting weak or something like that?

OP, you can try capping the return fuel line temporarily. I use vacuum caps and one of those fuel line hose clamps. Prime the system and this is what your fuel pump is able to produce at maximum pressure.

When I was doing troubleshooting on my 99 Silverado I recall my pump maxed out at 100 psi. That truck still has the original fuel pump and it's at 260k-ish. I've only done that once.

'03 will be a return-style fuel system so, yes, the fuel pressure regulator could incorrectly cause lower pressure by sending fuel back to the tank. Good catch.

 

[rockola1971]

At the time I bought it off Amazon, but I stopped buying OEM parts from Amazon. I’m confident it’s not the fuel pump because this issue was occurring before I replaced it. The fuel pressure specs are as follows before I replaced the fuel pump.

46 psi when key was on but engine off.
42 psi with engine running
42 psi after engine was ofF

If im reading this all correctly, these are readings that you got on your ORIGINAL fuel pump. Not the CURRENT fuel pump sitting in your tank. So what is the pressure coming from the CURRENT fuel pump?