2004 6.0 NV4500 Tahoe

[Dantheman1540]

My s10 did that. Pulled the assembly to replace the pump and the little hose from the pump to the top of the sending unit was rubbing the spring and it had worn a tiny hole in it. That caused it to bleed off until I tried to start it. I had no other issues, just long crank on initial startup

I was thinking something like that, if it was the actual pump failing it likely wouldn't WOT well.

Time to drop the tank and see what’s going on. How old is the pump?

FML I might go the "Cut the hole in the floor method", the pump is probably the factory 2004 pump. Not sure what I want to replace it with either, not sure if the flex-fuel pumps are any better or direct fit, it's been a while since I've looked at fuel stuff.

 

[Rocket Man]

I was thinking something like that, if it was the actual pump failing it likely wouldn't WOT well.


FML I might go the "Cut the hole in the floor method", the pump is probably the factory 2004 pump. Not sure what I want to replace it with either, not sure if the flex-fuel pumps are any better or direct fit, it's been a while since I've looked at fuel stuff.

It’s not hard at all to drop the tank. Way easier than going through the hassle of cutting and patching a hole in the floor. Unless you plan on replacing the pump on a regular basis. Just siphon or pump all the fuel out. Pull the filler hose off and stick a hose in. Also, FYI, the FPR is part of the pump assembly on yours so it could be that. On my 02 it’s on the fuel rail. Mine was failing and letting pressure bleed off and I was able to replace it easily. If yours is bad, replacing the pump assembly is the best bet since you might as well while you’re there. Plus the age of the pump. It’s going to go out sooner or later, better to do it when it’s not a ways from home.

 

[Fless]

I was thinking something like that, if it was the actual pump failing it likely wouldn't WOT well.


FML I might go the "Cut the hole in the floor method", the pump is probably the factory 2004 pump. Not sure what I want to replace it with either, not sure if the flex-fuel pumps are any better or direct fit, it's been a while since I've looked at fuel stuff.

FF pumps are different from non-FF; I don't believe they're interchangeable. The FF pump has two fuel lines on it, and I think non-Flex has 3.

 

[Dantheman1540]

It’s not hard at all to drop the tank. Way easier than going through the hassle of cutting and patching a hole in the floor. Unless you plan on replacing the pump on a regular basis. Just siphon or pump all the fuel out. Pull the filler hose off and stick a hose in. Also, FYI, the FPR is part of the pump assembly on yours so it could be that. On my 02 it’s on the fuel rail. Mine was failing and letting pressure bleed off and I was able to replace it easily. If yours is bad, replacing the pump assembly is the best bet since you might as well while you’re there. Plus the age of the pump. It’s going to go out sooner or later, better to do it when it’s not a ways from home.

Ugh, I so don't want to mess with the tank period. I can't remember if these are return or returnless. I know 05 is returnless because I converted my RCSB to return style with a Walbro450, but the Walbro only lasted about 2 years which kinda ticked me off.

I guess I'd be a fool to throw a factory pump in if they are only good for 450ish hp and I eventually plan to do some mild forum of boost. Maybe go with a brushless Aeromotive this time around.

FF pumps are different from non-FF; I don't believe they're interchangeable. The FF pump has two fuel lines on it, and I think non-Flex has 3.

That's what I figured, darn, I was hoping for an easy OEM upgrade.

 

[Fless]

Here's a top pic of my '04 Flex fuel tank with a new pump gasket and ring. Top in pic is front of truck. Evap lines are on the righthand (passenger) side and fuel lines would be on the lefthand side on top. Seems like the fill tube vent line connection (aqua colored) on mine is next to the fill tube connection, but I think non-Flex are different there, too.

 

[Dantheman1540]

Here's a top pic of my '04 Flex fuel tank with a new pump gasket and ring. Top in pic is front of truck. Evap lines are on the righthand (passenger) side and fuel lines would be on the lefthand side on top. Seems like the fill tube vent line connection (aqua colored) on mine is next to the fill tube connection, but I think non-Flex are different there, too.

View attachment 353866

Great picture! I will have to get under mine and compare best I can.

 

[Rocket Man]

I guess I'd be a fool to throw a factory pump in if they are only good for 450ish hp and I eventually plan to do some mild forum of boost. Maybe go with a brushless Aeromotive this time around

@randeez says “ here’s the rabbit hole, come on in”…

 

[Dantheman1540]

No! Please no! Not the dreaded rabbit hole!

What pump do you have @Rocket Man ?

 

[Rocket Man]

No! Please no! Not the dreaded rabbit hole!

What pump do you have @Rocket Man ?

Stock pump for mine. The 02’s had a big enough pump for 450 Hp, I’m not planning on anything past that. I did try a smaller pulley on the blower but ran into injector duty issues and from what I can figure I would need a bigger (or dual) pump, 2 bar speed density tune as well as injectors. I backed away from that rabbit hole. Whipple made the decision easier because you need to pull the blower to swap injectors out. Stupid design but I’m not pulling that thing. The Allen head bolts in the back by the firewall are about impossible to get to. I’m ok with what it is. I’m all about dependability now, and I know if I start adding more power I’ll just start breaking other stuff anyway.

 

[Dantheman1540]

Stock pump for mine. The 02’s had a big enough pump for 450 Hp, I’m not planning on anything past that. I did try a smaller pulley on the blower but ran into injector duty issues and from what I can figure I would need a bigger (or dual) pump, 2 bar speed density tune as well as injectors. I backed away from that rabbit hole. Whipple made the decision easier because you need to pull the blower to swap injectors out. Stupid design but I’m not pulling that thing. The Allen head bolts in the back by the firewall are about impossible to get to. I’m ok with what it is. I’m all about dependability now, and I know if I start adding more power I’ll just start breaking other stuff anyway.

I feel that on the reliability part.

I think I'm gonna do a OEM replacement bucket/pump and in the future do an inline Boost-a-pump for future power. The guys at PT.net talked me into it. the BAP should supply enough fuel for 600+ and thats more than I ever want in this thing.

 

[Dantheman1540]

So is my fuel pump dying? Can’t remember what oem specs are but I thought 50primed and 40psi bleed down and hold was normal

 

[Fless]

Shoot. Seems like it should be a bit higher and not bleed down so quickly when not running. Leaky injector? Bad fuel pump or FPR?

KOEO specs for NBS V8 engines:
Non-Flex: 55 to 62 psi
Flex: 48 to 54 psi

 

[Fless]

What kind of pressure when it's running at various RPMs?

 

[Rocket Man]

So is my fuel pump dying? Can’t remember what oem specs are but I thought 50primed and 40psi bleed down and hold was normal

Leave it on for awhile. If it’s the FPR or a small leak it will show over time.

 

[George B]

Did you bleed the air out of the tester hose?

 

[Dantheman1540]

Did you bleed the air out of the tester hose?

Damn I’m an idiot, no I didn’t I was super rushed.

Leave it on for awhile. If it’s the FPR or a small leak it will show over time.

I will have to do further testing Friday when I have more time and I will leave it for longer to see.

What kind of pressure when it's running at various RPMs?

I didn’t get time to check I was in a rush but I’ll check that Friday

Shoot. Seems like it should be a bit higher and not bleed down so quickly when not running. Leaky injector? Bad fuel pump or FPR?

KOEO specs for NBS V8 engines:
Non-Flex: 55 to 62 psi
Flex: 48 to 54 psi

Huh didn’t know it was that high but makes sense most people set their adjustable FPRs to 58. Ill inspect better for a leaky injector tomorrow when I leave for work.

 

[randeez]

Should've kept the taco.

Also
58psi=400kpa
43psi=300kpa
That's where the oddly specific psi comes from

 

[Dantheman1540]

Should've kept the taco.

Also
58psi=400kpa
43psi=300kpa
That's where the oddly specific psi comes from

I’ll probably swap all my **** into the taco tomorrow or Friday, it takes me a good 15minutes to swap all my **** and I always end up forgetting stuff if I swap at 1030pm after class in the dark or 6am before work in the dark.

Ahhhh that explains the oddly specific psi, guess I’ll order a bucket assembly off Amazon just in case further testing proves it to be the pump. If not I’ll return it lol

 

[Dantheman1540]

Alright more testing was done this morning, the first prime pumped to 52 and bleed down to 40 again, tried to start and no start after 10 seconds, cycled the key again and got 52 which bled down to 40 but immediately started like it usually does. Idle pressure was between 50-55 same with WOT neutral revving, I have not driven with the gauge hooked up yet although I have no reason to think it would be any different because it drives and shows perfect AFR during all driving conditions.

Yes, I did bleed the pressure out of the gauge hose this time, yayy I smell like fuel now.

At this point, although the pressures arent up to 62 I personally don't believe it's a fuel pump problem since the pressures are consistent and when it won't start on that first crank it has the exact same pressure as it does when it does start on the second crank. If there was a noticeable difference between the initial crank FP and the second crank FP I would say its likely a fuel pump/bucket/FPR issue.

Since the issue shortly before this was related to a cam position sensor is it possible I need to do a crank relearn or anything? I'm fairly certain it can be done with HPT special commands and functions. Or is it possible I have an INOP cam position sensor? I cleaned the area fairly well before I installed it but I installed it blindly giving it the reach around.

 

[George B]

Do you have a tech2? Do a case relearn.