# Stalling/bucking after sitting



## Bvogt (Dec 19, 2021)

At first, fuel filter stood out, but if changed 6 months ago it should be fine. Any codes?


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## DavGr (Dec 12, 2019)

Bvogt said:


> At first, fuel filter stood out, but if changed 6 months ago it should be fine. Any codes?


No CEL, I need to pull the codes next time it happens. Almost tempted to have the scanner with me and go that way intentionally a couple of times to see if it’s consistent. It’s done it every time i’ve had to wait at that stop light for at least 4mo now but I only go that way maybe once or twice a month. At first I thought it was due to almost being out of fuel (low fuel light was on when it did it once and had just under 1/4 a tank one other time) but it’s done it on a near full tank twice now. I’m still thinking it’s fuel system related, just not sure where to look. Reminds me of when you get air in the fuel and need to purge the fuel filter on a larger diesel like my F250.


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## Bvogt (Dec 19, 2021)

I’d definitely check your fuel pressure. Mine a Gen 1 and it purges itself be cycling the key, as yours does too, couldn’t hurt to pop off that filter. Start simple. Good luck man. There are some real knowledgeable Gen 2 and techs on here.


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## Barry Allen (Apr 18, 2018)

Check to see if your low pressure pump is working. Easy way to do that might be to drain the filter and then turn on the service mode to pressurize the filter as if you just changed it. If all else is quiet you should be able to hear the WHIRR of the pump as it quickly pumps fuel through the filter housing, and it will change pitch as everything fills up. If you've changed the fuel filter yourself, you'll recognize the WHIRR sound and hear some fuel gurgling in the housing as it's all pressurized and filled up.

You don't have a pump in good working order to compare the sound so you might have to guess. If you hear the pump and it sounds weak to you, or doesn't sound like it's pumping much at all, or sounds like it's taking forever to fill the filter up with fuel, maybe the LPFP is going bad? You'll have to guess at the sound.

A failing or broken LPFP can cause problems with the expensive HPFP because that HPFP then has to draw a vacuum to suck the fuel all the way forward. It's not meant to do that and it adds wear and tear to the HPFP. The HPFP is designed to have good pressure behind it from the LPFP so that it has a steady supply of fuel from the tank for lubrication and cooling.


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