Fuel level Issues 2004 Suburban 1500 Flex fuel

[grimspyder]

I have always had a weird issue with my fuel level.
It reads the level of fuel correctly. When it shows empty it is empty and when I fill it up it shows full. But' It has an issue where the if the level falls below a quarter tank it will not start again. When you try to start it, It will turn over attempt to start for 1/2 a second and die. When you add fuel and it goes past 1/4 tank it starts right up, no issues. But I can drive it completely empty and it will not shut down if I started up before quarter tank.
I bought the Suburban back in 2017 and it has always been like this, not really an issue ( I just always filled up before quarter tank).
But lately it seems that that 1/4 tank level is going up. Today I got semi stranded when at about 3/8 tank. Same issue didn't want to start. I first tried to clear fault codes to see if that would fix the issue (There where no fault codes) But that didn't work. I then disconnected the battery and reconnected it. And it started right up, no issues.
So the problem is not the sending unit ( I think ). So I do not want to replace the fuel pump Assembly (I have recently modified with an Aeromotive 11569 Fuel Pump ).

My question is. Is there a way to disable/adjust what ever is causing the ECU to cut fuel/spark to the engine when it hits a certain fuel level?

After the fuel pump modification, when the suburban is on, it pumps fuel (It is directly connected to battery (with relays and fuses)). So I do not need any fuel pump management from the ECU.
The vehicle runs absolutely perfect outside of that issue with the weird fuel cutoff at a 1/4 tank or so.

Thanks

[kevin87turbot]

Put a fuel pressure gauge on it and see if it's simply a fuel pressure issue.

Occasionally, I'll see a bad cam position sensor or bad connector on the cam position sensor that will also cause a starting issue.

[grimspyder]

When I swapped out the fuel pump I did a pressure test it was about 51 - 55 PSI if i remember correctly.
A cam position sensor could cause that issue? Interesting?
I guess I could see how it could cause the ECU to cut fuel/spark. But its weird that it at 1/4 tank, I wonder how cam position sensor deals with fuel management? I'm going to have to look into it.
Thanks.

[TheMechanic]

Wild guess here but I have replaced pumps (there is a bulletin but don't know if it is for your specific application) that have burned/bad/high resistance connections on the inside of the tank at the pump and at the (bulkhead) connection on the fuel pump assembly. Maybe under a 1/4 it does not have the cooling effect of the raw fuel to give it a slightly better connection. There is a new style pump assembly also to fix the dreaded wear hole on the supply line right off the pump. They rub against the spring loaded rod.
As a diag I would test the theory by crawling under during the trouble to see if you can feel and hear the pump activate. If not have someone get in the vehicle from a key of engine off and attempt to start while you bang on the bottom of the tank. If it starts it's time to pull the tank

[2xLS1]

When I swapped out the fuel pump I did a pressure test it was about 51 - 55 PSI if i remember correctly.
A cam position sensor could cause that issue? Interesting?
I guess I could see how it could cause the ECU to cut fuel/spark. But its weird that it at 1/4 tank, I wonder how cam position sensor deals with fuel management? I'm going to have to look into it.
Thanks.

it doesn't. All the cam position sensor does is tell the PCM when the cylinders are at TDC compression stroke or TDC exhaust stroke. It has nothing to do with fuel delivery or fueling. It will run without a CMP signal. The pcm will fire the plugs when it thinks the cylinders are at TDC compression and if it doesn't start then it will wait 180 degrees of crank rotation and try that. It will continue to fire syncing off what made it run until the next key cycle. It has to see a CMP code to do that. If no CMP code is set it won't try.

[SiriusC1024]

CMP is for injection timing, not spark.

[2xLS1]

It controls both in sequential fire injection buy you can inject fuel 180 degrees out of phase with correct spark phasing and the engine will run. Otherwise batch fire injection would have never worked.