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MP8 looses fuel overnight


thom2and
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I have a 2008 granite with a MP8. Truck has 55,000 miles and about 2200 hrs. It's looseing fuel overnight. In the morning when I try starting it, it will fire and idle for what seems like less than a second then dies. When I try starting it again it just cranks and cranks, if you keep on it will finally start.

What seems to work the best (before trying to start engine) is to open the hood and use the hand fuel primer until I get pressure.(anywhere from 30 to 60 pumps with the primer, I can here a gurgle in the fuel tank when doing this) Then it will start immediately, but will stumble and smoke a little until air is cleared from the system.

Actions I have taken: replaced check valve on front of head, bypassed Davco fuel filter/heater, changed fuel filters, checked for loose fuel lines.

Engine performance seems good. Hot starts are not a problem. This has been an ongoing problem all summer. Just recently I have had 2 different fault codes: p94 and pp328. The codes have come when truck is just started, after engine levels out, the lightening bolt disappears.

Any thoughts or suggestions?

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There is a plastic cap right behind the hand primer pump, when you are using the hand pump is there a collection of fuel/wet around the cap? If so, the o-ring below the cap is bad and is the cause of the fuel drain back. Replace the filter stand, I've tried to replace the o-ring-doesn't work. If not, both fuel filters nipples have anti-drain back check valves in them, make sure they move freely. Any fitting from the tanks up to the inlet of the transfer pump could be the cause of your drain back issue. Has anything been serviced recently?

good luck

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There is a plastic cap right behind the hand primer pump, when you are using the hand pump is there a collection of fuel/wet around the cap? If so, the o-ring below the cap is bad and is the cause of the fuel drain back. Replace the filter stand, I've tried to replace the o-ring-doesn't work. If not, both fuel filters nipples have anti-drain back check valves in them, make sure they move freely. Any fitting from the tanks up to the inlet of the transfer pump could be the cause of your drain back issue. Has anything been serviced recently?

good luck

Thank you for the suggestions. I'll look into it. This is a strange deal. On a rare occasion it will hold its prime, but rare.

Also, I have only one filter on the filter housing. The other is capped.

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The inlet of the davco filter has a check valve remove and inspect, make sure the spring and check ball are not damaged or blocked open with debris.

I have completely bypassed the davco and it still drains back. I also installed another check valve to ensure the davco wasn't leaking back. Thanks.

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There is a plastic cap right behind the hand primer pump, when you are using the hand pump is there a collection of fuel/wet around the cap? If so, the o-ring below the cap is bad and is the cause of the fuel drain back. Replace the filter stand, I've tried to replace the o-ring-doesn't work. If not, both fuel filters nipples have anti-drain back check valves in them, make sure they move freely. Any fitting from the tanks up to the inlet of the transfer pump could be the cause of your drain back issue. Has anything been serviced recently?

good luck

The plastic cap seems to be dry while priming. The check valve on the secondary nipple my be damaged. The ball seems to move ok now, but I have about 1/4" of free travel before there is any resistance from the spring. Once the ball makes contact with the spring I have another 1/2 inch of travel. If the check valve is damaged. Is it possible for fuel to drain back through the return line?

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  • 2 weeks later...
  • 2 years later...
  • 1 year later...
8 minutes ago, fjh said:

yup high on the list of suspects! however the symptom is a bit odd as cups usually presents it self as a no start no fire at first crank ,not fire and die! or long crank times and stumble start up!

 

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  • 2 weeks later...

I had a mp7 no start. Supposedly started out as a hard start. Found a check ball in the primary fuel filter housing stuck open. I changed it and thought for sure it was solved. Didn't change a thing. After it sat for 5 minutes it would not restart. Changed the injectors and cups. Problem solved.

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