Rough start on 1/4th tank?

diezelraccoon · Aug 22, 2024

I have an 03 Tahoe with the 5.3. I’ve noticed that once it gets down to about 1/4th a tank or lower and sits all night, when I go to start it it takes a few extra cranks about another 1-2 seconds and then fires up.

Could it be fuel pump related? I’ve never had a vehicle that rough starts when it’s lower on gas.

OR VietVet · Aug 22, 2024

Does sound like fuel pressure bleed off and could be the pump or an injector or or or......Attach a fuel pressure gauge and start and then shut off and let sit and monitor the gauge to see if holds a reasonable amount of pressure.

I will tell you what I tell my girl and anyone that will listen, think of 1/4 tank as empty.

Marky Dissod · Aug 23, 2024

diezelraccoon said:
'03 Tahoe, 5.3L ... once it gets down to about 1/4 tank or lower and sits all night,
when I go to start it it takes a few extra cranks about another 1-2 seconds and then fires up.

Could it be fuel pump related? I’ve never had a vehicle that rough starts when it’s lower on gas.

Could be a nut behind the wheel.
Fuel pumps are like fish - they live longest submerged in their element, protected from exposure to the air.

OR VietVet said:
I will tell you what I tell my girl and anyone that will listen, think of 1/4 tank as empty.

Once was hangin out with friends, idling parked on a steep hill, gas gauge read a wee lil bit over 1/4 tank.
In about 10min, despite there in fact being at least 6.5 gallons in the tank, it 'ran out of gas' because the fuel pump was exposed.
Had to roll it downhill in neutral til I could find a spot to level it out, started right up 2min later, because it wasn't out of gas.

Totally different time, was trying to take a very long offramp 24MpH faster than the speed advised on the yellow sign.
Despite there being at least 6.5 gallons in the tank, guess what happened?
Managed to pull over by enough to let everyone else by, started right up 2min later.

Once the gauge says under 1/4, drive like a wuss and start looking for a gas station.

rockola1971 · Aug 24, 2024

Assuming OP's driveway is relatively level, there would be no chance of the fuel pump being unsubmerged with roughly 5-6gals of gas in the tank at 1/4 tank. Even at a decent incline the pump would never be unsubmerged because the sump area that fuel pump sits in is pretty deep so gas is trapped in there by design. It would take a seriously sharp angle of incline with the front of the vehicle pointing downward for there ever to be a chance of the pump becoming unsubmerged. I would start with the basics and check fuel pressure(KOEO) and bleed off.

Fless · Aug 24, 2024

rockola1971 said:
Assuming OP's driveway is relatively level, there would be no chance of the fuel pump being unsubmerged with roughly 5-6gals of gas in the tank at 1/4 tank. Even at a decent incline the pump would never be unsubmerged because the sump area that fuel pump sits in is pretty deep so gas is trapped in there by design. It would take a seriously sharp angle of incline with the front of the vehicle pointing downward for there ever to be a chance of the pump becoming unsubmerged. I would start with the basics and check fuel pressure(KOEO) and bleed off.

^^^ THIS ^^^

You might also have an inaccurate fuel gauge. When it gets to 1/4 tank, fill it up on "slow" to the first click of the pump (don't be tempted to keep pumping after the first click -- that can saturate the evap system and cause other problems) and see how many gallons it takes. Subtract that from the tank capacity and you'll have a better idea of how much fuel is still remaining.

Matahoe · Aug 24, 2024

Rough start or extended crank start? I guess they could be related. I had to replace my EVAP canister, purge and vent valve years ago to fix my extended crank issue. But that was when I had the tank out to clean it, inspect the EVAP lines and replace the fuel pump. I think it was flooding the engine with fumes or something like that. The PCM does a few housekeeping steps on the EVAP stuff when you fill the tank past a certain way to make sure it's a sealed system. The fuel tank pressure sensor on top of the pump is critical in order for EVAP system to work at all. I know that.

diezelraccoon · Aug 24, 2024

Matahoe said:
Rough start or extended crank start? I guess they could be related. I had to replace my EVAP canister, purge and vent valve years ago to fix my extended crank issue. But that was when I had the tank out to clean it, inspect the EVAP lines and replace the fuel pump. I think it was flooding the engine with fumes or something like that. The PCM does a few housekeeping steps on the EVAP stuff when you fill the tank past a certain way to make sure it's a sealed system. The fuel tank pressure sensor on top of the pump is critical in order for EVAP system to work at all. I know that.

Extended crank is what mine is doing. Evap can, evap solenoid, the evap valve on top of engine were all replaced.

Matahoe · Aug 24, 2024

Check the fuel pressure like Will suggested in the first reply. That's a pretty good starting point assuming all the basics are good. Any check engine light? If it's been reset you will want to take the truck for a spin on the highway and some stop and go traffic to see if it comes back. Up to 50 or so miles over the course of a few days. This kind of check is used by the PCM to see if the truck can pass EPA emissions standards. The check engine light should come on or flash if it fails a test. If your check engine light is flashing at any point then you got a misfire and continued driving that way could kill the catalytic converter. So stop at that point and investigate. Don't drive the vehicle until fixed.

Also test the fuel pressure regulator FPR for leaks and proper operation. That's a simple check and often overlooked because very often people don't realize they have one. But there is for 99-04 models. Not for 05 as that type fuel system is return-less which is what I have.

Do those recommend checks, gather the results and let us know what you got.

diezelraccoon · Aug 26, 2024

Matahoe said:
Check the fuel pressure like Will suggested in the first reply. That's a pretty good starting point assuming all the basics are good. Any check engine light? If it's been reset you will want to take the truck for a spin on the highway and some stop and go traffic to see if it comes back. Up to 50 or so miles over the course of a few days. This kind of check is used by the PCM to see if the truck can pass EPA emissions standards. The check engine light should come on or flash if it fails a test. If your check engine light is flashing at any point then you got a misfire and continued driving that way could kill the catalytic converter. So stop at that point and investigate. Don't drive the vehicle until fixed.

Also test the fuel pressure regulator FPR for leaks and proper operation. That's a simple check and often overlooked because very often people don't realize they have one. But there is for 99-04 models. Not for 05 as that type fuel system is return-less which is what I have.

Do those recommend checks, gather the results and let us know what you got.

I checked the fuel pressure regulator. Seems to be fine. When I pulled the vacuum hose off of it it wasn’t spitting out any gas.

As far as the fuel pressure what should a normal range PSI be?

new2yukon · Aug 26, 2024

On my F150 forum they say this is common at 1/4 tank or less due to excess vapors in purge system. Once you get those clear then it will start right up. Different vehicle, yes, but prob similar designs.

Rough start on 1/4th tank?

diezelraccoon

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OR VietVet

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Marky Dissod

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rockola1971

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Fless

Matahoe

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diezelraccoon

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