Stumble/Hesitation AND stalling: *solved, fuel pump*

[Bill 1960]

No good answer from dissection of the pump. It is a somewhat complicated unit, all the fuel flow is not just one way. There’s a little venturi nozzle at the base as well as some sort of valve at the top of the filter canister that looks like a regulator or bypass. Plus the path through the filter and out to the engine. So 3 ways fuel could exit the pump.

Perhaps some of the plumbing is to eject entrained air and it was failing? There was plenty of good old Texas dirt in the filter and some residual crud in the bucket that surrounds the pump.

 

[Doubeleive]

No good answer from dissection of the pump. It is a somewhat complicated unit, all the fuel flow is not just one way. There’s a little venturi nozzle at the base as well as some sort of valve at the top of the filter canister that looks like a regulator or bypass. Plus the path through the filter and out to the engine. So 3 ways fuel could exit the pump.

Perhaps some of the plumbing is to eject entrained air and it was failing? There was plenty of good old Texas dirt in the filter and some residual crud in the bucket that surrounds the pump.

hook that fuel pressure gauge back up and see what it shows now, my bet is it's a hair higher at idle, mine sits right at 44 most of the time

 

[Bill 1960]

hook that fuel pressure gauge back up and see what it shows now, my bet is it's a hair higher at idle, mine sits right at 44 most of the time

That’s a good idea. But is this Harbor Freight gauge accurate enough to tell the difference LOL.

If I do I’ll read the live data with my scan tool also and see how it compares to what the ECM sees.

 

[Doubeleive]

That’s a good idea. But is this Harbor Freight gauge accurate enough to tell the difference LOL.

If I do I’ll read the live data with my scan tool also and see how it compares to what the ECM sees.

more of a curiosity thing, if it shows a smidge better maybe that's all it was, like you said when it got hot, unrelated but I had a smart phone that died a fairly slow death I figured it was the cpu taking a c-rap, when I bought a new one I had the option to connect them together with a cable to transfer all the data over but the old phone had got so bad it wouldn't even boot anymore so I stuck it in the freezer with the cable hanging out, let it sit a few minutes and then reached in and turned it on, sure enough it booted and ran just long enough to transfer the data over to the new phone. heat kills

 

[torch]

I would replace the FPCM just because it is a 2008. They had a lot of trouble with water and junk getting inside the module. I think there was a recall where the dealer would put sealer around the seams of the FPCM. Also at some point GM added a rubber shield/flap in front of the FPCM to protect it from road debris. I have a 2009 Tahoe and it would stall when making right hand turns and set a P069E. It a lot of water had gotten inside the module and the sloshing water during the turn and killing the power to the pump. I just ordered a new pre-programmed FPCM and all is good now. If you don't have the rubber shield in front of the FPCM I would suggest you make one for your off roading.

 

[Bill 1960]

After 5 days driving on the new fuel pump I’ll call it and say that was the cause of both issues. Hasn’t misfired once since the pump. And I’ve done a lot of 4x4 and 4L operation with no stalling.

The part was a Delphi FG1054. Took the shop 2 hours to swap it in.

I also bought the Dorman FPCM / FSCM part number 601-022. Which is plug and play no dealer flash required. I haven’t installed that because I wanted to evaluate the results of the pump change. Later this week I’ll install it and run it for a week or so to verify it, then I’ll have a known good spare. I’ll also be fabricating a skid plate to shield it.

Plugs and wires are on hand. I’ll install them at my convenience since it’s back to running fine.

Thanks to everyone who helped work through these problems!

 

[Geotrash]

After 5 days driving on the new fuel pump I’ll call it and say that was the cause of both issues. Hasn’t misfired once since the pump. And I’ve done a lot of 4x4 and 4L operation with no stalling.

The part was a Delphi FG1054. Took the shop 2 hours to swap it in.

I also bought the Dorman FPCM / FSCM part number 601-022. Which is plug and play no dealer flash required. I haven’t installed that because I wanted to evaluate the results of the pump change. Later this week I’ll install it and run it for a week or so to verify it, then I’ll have a known good spare. I’ll also be fabricating a skid plate to shield it.

Plugs and wires are on hand. I’ll install them at my convenience since it’s back to running fine.

Thanks to everyone who helped work through these problems!

Awesome!!! So glad you got it sorted out!

 

[Joseph Garcia]

Thank you for closing the loop and confirming the source of your issue. Much appreciated.

 

[jeremiahm]

I replaced my fuel pump this weekend as well. Had the rough idle at stops, also a spike in RPM when coming to a stop (shift to 1st?) and had experienced some stalls and crank/no starts the last two weeks, including a tow. 3 days of driving and idle smooth and the spike in RPM is virtually gone, no stalls either. My MPG seems to be +1 as well. Pump was making some noise that was hard to notice until I could get close to it (I cut a hole in the floor). New pump is almost silent. Used same Delphi pump as @Geotrash. Truck has 150k on it.

 

[OR VietVet]

I still cannot wrap my head around cutting a hole in the floor. Just sayin'.

 

[jeremiahm]

I have done it twice. I can't take the beating of the concrete on my back so cutting a hole is worth it. I hit the cuts on the money this time so it came out nice. I plan on keeping it a while so I may need to use it again... This is on my 207 Yukon XL Denali.

 

[bdbull]

I replaced my fuel pump this weekend as well. Had the rough idle at stops, also a spike in RPM when coming to a stop (shift to 1st?) and had experienced some stalls and crank/no starts the last two weeks, including a tow. 3 days of driving and idle smooth and the spike in RPM is virtually gone, no stalls either. My MPG seems to be +1 as well. Pump was making some noise that was hard to notice until I could get close to it (I cut a hole in the floor). New pump is almost silent. Used same Delphi pump as @Geotrash. Truck has 150k on it.

I have a rough idle on my '10 Avalanche as well. Been battling it for a long time now with no resolution. No codes, no stalls, but it sure feels like it's just a smidge from stalling when I'm sitting at a light. I've also experienced an issue that I think might be the same as your "spike in RPM when coming to a stop." There have been times when coming to a stop, right before finally stopping, where it seems like the truck tries to accelerate instead of decelerate. I haven't actually noticed the RPM's when it happens, but it makes sense. I do know it scared the ever living snot out of my teenager as he's learning to drive.

Think I'm gonna look into swapping out the fuel pump and cross my fingers that will fix it. I've got 210k miles and as far as I know, the fuel pump is original to the truck.

btw, here is a video of my RPM gauge I took yesterday while sitting at a light. You can see it jumping around as I just sit there.

 

[swathdiver]

I have a rough idle on my '10 Avalanche as well. Been battling it for a long time now with no resolution. No codes, no stalls, but it sure feels like it's just a smidge from stalling when I'm sitting at a light. I've also experienced an issue that I think might be the same as your "spike in RPM when coming to a stop." There have been times when coming to a stop, right before finally stopping, where it seems like the truck tries to accelerate instead of decelerate. I haven't actually noticed the RPM's when it happens, but it makes sense. I do know it scared the ever living snot out of my teenager as he's learning to drive.

Think I'm gonna look into swapping out the fuel pump and cross my fingers that will fix it. I've got 210k miles and as far as I know, the fuel pump is original to the truck.

btw, here is a video of my RPM gauge I took yesterday while sitting at a light. You can see it jumping around as I just sit there.

Try checking your wires. I had a wire separate from a boot and didn't know it. How old are your plugs? A Tech-2 would be nice to have to see what's going on inside.

 

[bdbull]

Try checking your wires. I had a wire separate from a boot and didn't know it. How old are your plugs? A Tech-2 would be nice to have to see what's going on inside.

Plugs and wires were replaced at 190k, so they are right at 20k. I'll check them out just in case that would be an easy fix.

 

[bdbull]

Plugs and wires were replaced at 190k, so they are right at 20k. I'll check them out just in case that would be an easy fix.

Haven't gotten to check everything yet, but it did it sitting in park in a parking lot just now. So it looks like it's not just while in drive. Actually thought it was gonna shut off.

 

[Fless]

Before you go and change that fuel pump out on a guess, why not rent a fuel pressure gauge and do the test? Best case it might rule it out.

 

[bdbull]

Before you go and change that fuel pump out on a guess, why not rent a fuel pressure gauge and do the test? Best case it might rule it out.

Is it sufficient to use a OBD2 reader to test that or would it be better to rent a gauge from the parts store?

 

[Fless]

Best to rent the gauge and check it at the fuel rail.

 

[89Suburban]

I have done it twice. I can't take the beating of the concrete on my back so cutting a hole is worth it. I hit the cuts on the money this time so it came out nice. I plan on keeping it a while so I may need to use it again... This is on my 207 Yukon XL Denali.

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Thanks for taking the time to post the pics and measurements for the fuel pump access door/panel.

 

[OR VietVet]

When you check that fuel pressure gauge, get a long enough adaptor hose to allow for you to bring out at back of hood and tape to w/s to watch thru the whole driving/idling process.

You are actually pretty lucky that members are responding to this for you because the OP has already posted "Solved", on their thread.