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sprtkr1

Fuel prime again!

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I know this issue has been discussed many times on here before. I've read many threads on it. But few if any tell us how or if they ever got it fixed. My 08 cxu613 mp8 485hp loses prime in as little as 20 minutes. Used to hold it longer, but gettin worse with time. I've changed 2 check valves, fuel filter stand, seals on banjo bolts and checked fuel lines. The mack dealer checked injector cups in January and said they're ok. They've been changed twice. The only clue I have is I get air bubbles when the truck is running and after I shut it down in the driver's side fuel tank only. Maybe a cracked pickup tube? I promise to let y'all know if I ever get this problem solved. Is there a check valve on the back of the motor? Thanks for any thoughts.

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It sure sounds like cups or bad injector 

cumbustion in the fuel gallery.

Edited by fjh

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30 minutes ago, fjh said:

It sure sounds like cups or bad injector 

cumbustion in the fuel gallery.

Yup, sounds like the classic cup problem. There is a fuel regulator fitting in the head, the mp7 one is on top of the head, front drivers side. Not sure about the mp8 location, but I doubt that will be your problem.

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Thanks for the info. I'll have them checked again, by someone else this time.

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Found dampness around what looks like a weep hole on bottom of fuel transfer pump.  Could this have anything to do with it?

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Does this engine have the air purge system for the 7th injector? I have seen the air regulator  (mounted behind the air dryer) go bad and send system air pressure through the air purge system and back feed to the fuel system. A bad "T" check valve at the 7th inj. will do that as well. 

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Thanx for the ideas and thoughts on this. Sorry I didn't reply earlier but was on the road all week. Thinking about trying the fuel pump but leaning toward an injector problem. Becomes hard to start in under 5 mins after shutdown. Seems like losing prime that fast has to be one heck of a drain back. Truck runs good. No coolant in the fuel and no fuel in the oil. When I get this solved I'll sure let you know. Thanx again.

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Sorry, for got to say this does not have the air purge system.

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Well finally got the problem fixed. Congratulations to fjh and steeler. You were right. Even though I didn't want to believe it, it turned out that the number 4 injector was galled and cracked. Also had damaged the injector cup, so had all 6 cups replaced again even though they were replaced about a year ago. This thing has been nothing but a money pit literally since the day I drove it home. But for now it is starting real good. Thanx for everyone's input.

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21 hours ago, sprtkr1 said:

Well finally got the problem fixed. Congratulations to fjh and steeler. You were right. Even though I didn't want to believe it, it turned out that the number 4 injector was galled and cracked. Also had damaged the injector cup, so had all 6 cups replaced again even though they were replaced about a year ago. This thing has been nothing but a money pit literally since the day I drove it home. But for now it is starting real good. Thanx for everyone's input.

Yup don't thank us thank Volvo for giving you a place to put your money every year!

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