09 Tahoe engine dies at stop, no CEL

[markelee66]

We have a 2009 Tahoe LTZ with the 5.3L Flex Fuel. It has about 45k miles so very low mileage for the age and it's been well maintained. In the past few months we've had a few times, 3-4 where we experienced a long start. The starter turned way more than normal but once it started it was smooth, no rough idle or anything I think of when talking about a hard start. The other day when pulling up to a stop light there was a little surging. I thought it was the transmission trying to decide what gear to drop into. While sitting at the light the engine died. It cranked right back up but a moment later died again. It started again with no real issue and ran fine the half mile or so home. Once home and sitting in the driveway we could hear what we think was the fuel pump making a loud noise, basically a vibrating sound. There was no CEL and no pending codes when I hooked up the reader. Little bit of Google searching says fuel pump, throttle body, failed torque converter clutch. The fuel tank is not the original. It was replaced by a mechanic when trying to fix EVAP codes. We had hit the point we thought it was the valve/really that is in the tank and not serviceable, so I don't know any history of the tank and the fuel pump. Because of that and the unusually loud vibrating sound we're hearing from the fuel tank area, I'm leaning toward that being the problem. However, several of the searches point to a dirty throttle body. I'm wondering what the odds are of it being the throttle body with the lower mileage it has. I also found it has a fuel pump control module so I suppose the computer could be on the fritz. Looking for any input to get a solid diagnosis as I don't want to spend $400 on a fuel pump, drop the tank and all that work and it not be fixed. You know the drill. Thanks in advance for any infomation.

 

[Doubeleive]

check fuel pressure (with a gauge on the fuel rail) a kit is around $30 at harbor freight
check the battery cables and grounds
check and clean the throttle body/maf
all easy to do stuff

 

[mikez71]

Noise is a good bad-sign!
If you get a scanner on it, try and look up the 'fuel pump trim' value in the fuel system control module! (NOT fuel trims)

I'm just curious what it reads, especially if it ends up being your fuel pump...
(@swathdiver maybe interested too)

 

[West 1]

Noise in the fuel pump is a sure sign it is dead or close to dead. When they are making noise sometimes you can pound on the tank, big rubber hammer works, the pounding jostles the pump and they usually work for a bit before failing again.
I had one that you had to keep pounding to keep the pump working, it stopped as soon as the pounding stopped. We still used the bad pump to empty the tank through the fuel pressure port. A working pump can move 50-60 gallons per hour.

Losing fuel pressure is one of the few ways an engine stops while not causing a check engine light.

A in tank fuel pump is lubricated and cooled by the fuel running through it. Running out of gas even once and letting the pump spin with no fuel supply is fatal to a pump. It may last a short while after the empty tank but usually not long. I have been told 20 seconds of dry run is all it takes to damage the electric pump in the tank.

 

[markelee66]

Noise is a good bad-sign!
If you get a scanner on it, try and look up the 'fuel pump trim' value in the fuel system control module! (NOT fuel trims)

I'm just curious what it reads, especially if it ends up being your fuel pump...
(@swathdiver maybe interested too)

I'll have to check the trim. The live data gave a fuel psi of 58 when I first started it and it was idling at around 1250 rpm. It dropped to 43/44psi when the rpms dropped to the normal 750. If I get a chance to look for the other data I'll let you know what I find.

 

[markelee66]

Noise in the fuel pump is a sure sign it is dead or close to dead. When they are making noise sometimes you can pound on the tank, big rubber hammer works, the pounding jostles the pump and they usually work for a bit before failing again.
I had one that you had to keep pounding to keep the pump working, it stopped as soon as the pounding stopped. We still used the bad pump to empty the tank through the fuel pressure port. A working pump can move 50-60 gallons per hour.

Losing fuel pressure is one of the few ways an engine stops while not causing a check engine light.

A in tank fuel pump is lubricated and cooled by the fuel running through it. Running out of gas even once and letting the pump spin with no fuel supply is fatal to a pump. It may last a short while after the empty tank but usually not long. I have been told 20 seconds of dry run is all it takes to damage the electric pump in the tank.

Well it's never been run dry, at least not while I've been driving it. Can't speak for what may have happened at the shop but that was maybe a year ago so if it fails that quickly after a dry run, I'm going to guess that isn't the issue. It may just be the fact of an age thing and again, me not knowing the history of the part like I would if it hadn't been replaced as we are the only owners of it.

 

[mikez71]

I'll have to check the trim. The live data gave a fuel psi of 58 when I first started it and it was idling at around 1250 rpm. It dropped to 43/44psi when the rpms dropped to the normal 750. If I get a chance to look for the other data I'll let you know what I find.

Thanks! And those pressures look normal.

But the pump is still a prime suspect...

 

[Fless]

All good suggestions. I'll join with @Doubeleive to test the fuel pressure, KOEO, with a pressure tester. They can be "rented" at many auto parts stores for a deposit, which can be refunded when the set is returned.

Monitor the fuel pressure with your scanner; all the better if the scanner can graph. Catch it in the act, IF it's the cause.

 

[West 1]

When a fuel pump is not longer smooth and quiet in operation it is failing. It may have good pressure one minute and bad the next. I have never seen a fuel pump repair itself and become quiet and reliable without replacement.

Not trying to be a Debbie Downer but offering reality.

 

[Foggy]

Good Points made
Prob fuel pump as stated
Just a quick snapshot in time of normal fuel pressure is NOT
a great indicator of fuel pump health.. Mileage doesn't really matter
That pump is 17 years old

 

[markelee66]

Thanks! And those pressures look normal.

But the pump is still a prime suspect...

I think the slow starts in the past were a bit of warning shots, then the stalls were the fix it message. The pain in the butt part is it being sporadic so as we know that makes the diagnosis harder. I appreciate the input.

 

[markelee66]

Good Points made
Prob fuel pump as stated
Just a quick snapshot in time of normal fuel pressure is NOT
a great indicator of fuel pump health.. Mileage doesn't really matter
That pump is 17 years old

I agree the fuel pressure test doesn't carry any weight. It just shows it was working normally at the time of the reading and right now it's a sporadic issue. General consensus is the pump on this forum, just trying to be as sure as I can before dumping that much money and the blood/sweat into it.

 

[markelee66]

When a fuel pump is not longer smooth and quiet in operation it is failing. It may have good pressure one minute and bad the next. I have never seen a fuel pump repair itself and become quiet and reliable without replacement.

Not trying to be a Debbie Downer but offering reality.

Haha...you're not telling me anything I haven't already thought about, sorry Debbie...lol. I'm just trying to be as certain as I can before cutting the check on the part and expending blood & sweat on the swap.

 

[donjetman]

fuel pump relay in the under hood fuse box.

 

[swathdiver]

We have a 2009 Tahoe LTZ with the 5.3L Flex Fuel. It has about 45k miles so very low mileage for the age and it's been well maintained. In the past few months we've had a few times, 3-4 where we experienced a long start. The starter turned way more than normal but once it started it was smooth, no rough idle or anything I think of when talking about a hard start. The other day when pulling up to a stop light there was a little surging. I thought it was the transmission trying to decide what gear to drop into. While sitting at the light the engine died. It cranked right back up but a moment later died again. It started again with no real issue and ran fine the half mile or so home. Once home and sitting in the driveway we could hear what we think was the fuel pump making a loud noise, basically a vibrating sound. There was no CEL and no pending codes when I hooked up the reader. Little bit of Google searching says fuel pump, throttle body, failed torque converter clutch. The fuel tank is not the original. It was replaced by a mechanic when trying to fix EVAP codes. We had hit the point we thought it was the valve/really that is in the tank and not serviceable, so I don't know any history of the tank and the fuel pump. Because of that and the unusually loud vibrating sound we're hearing from the fuel tank area, I'm leaning toward that being the problem. However, several of the searches point to a dirty throttle body. I'm wondering what the odds are of it being the throttle body with the lower mileage it has. I also found it has a fuel pump control module so I suppose the computer could be on the fritz. Looking for any input to get a solid diagnosis as I don't want to spend $400 on a fuel pump, drop the tank and all that work and it not be fixed. You know the drill. Thanks in advance for any infomation.

Pressure is good at idle once warmed up. Pump's have one-way valves and can bleed down pressure as they age. The fuel system can also be affected by worn or improper oxygen sensors calculating the alcohol content incorrectly. Can you check the alcohol content?

Can you check the fuel pressure while driving? It should not vary by more than 2 psi or so while cruising or driving. If the pressure drops or doesn't build up at WOT to 58 psi then she's about ready for replacement. The noise however is a sign that something isn't well down inside the tank. If you're certain that's where it's coming from?

 

[Fless]

fuel pump relay in the under hood fuse box.

I wouldn't think it would have that relay if it has the FPCM, would it?

 

[LsHart]

Is there an update for this??

 

[markelee66]

Is there an update for this??

Since the general consensus was fuel pump, I ordered one. Dropped the tank & found charcoal in the tank & all around the pump after it was supposedly cleared by the shop. So, I also bought a new charcoal canister. I fully dried the tank, cleaned it out completely, checked all the lines & the relay under the hood & installed the new canister & fuel pump. That was probably end of March or early April. So far no issue with the engine dying. The long start however was still happening on rare occasion. I had a neighbor with a high end diagnostic computer check & no errors or out of spec readings. After consulting with a friend who owns a shop but is out of state, I have recently replaced the camshaft positioning sensor. So far, so good but I'm not saying it's fixed until more drive time relapses with no long start.

 

[LsHart]

So, probably fixed. That's a good thing.just need results on these type of issues. For the next guy.

 

[Fless]

Since the general consensus was fuel pump, I ordered one. Dropped the tank & found charcoal in the tank & all around the pump after it was supposedly cleared by the shop. So, I also bought a new charcoal canister. I fully dried the tank, cleaned it out completely, checked all the lines & the relay under the hood & installed the new canister & fuel pump. That was probably end of March or early April. So far no issue with the engine dying. The long start however was still happening on rare occasion. I had a neighbor with a high end diagnostic computer check & no errors or out of spec readings. After consulting with a friend who owns a shop but is out of state, I have recently replaced the camshaft positioning sensor. So far, so good but I'm not saying it's fixed until more drive time relapses with no long start.

Verify that a CASE relearn was done after the cam sensor change. Not syncing the cam and crank sensors can cause intermittent long crank time.