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OJ Avery

Another MP7 Fuel Issue

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Hi all. I have an issue with a 12 mp7 10 emissions. Its a NYS DOT truck which is in a lot of salt. The fuel filter housing had rotted away and the cooler ends were barely there. I replaced most of the lines going to the filter head. I can not get it to prime!! I took the feed hose from the tank off, blew it out both ways, still can't get it to prime. What gives

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You have a hand primer on it?

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Sounds like the suction line is compromised meaning a small air leak such as a pinhole. I don't section lines or put new fittings on old but rather replace wholesale. No comebacks that way.

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Posted (edited)

Mp8, I had took 200 pumps on priming a fuel filters change.

volvo got it going on!!! Lol!!!

Edited by 1965

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Those problematic ones I use a "Carter" electric fuel pump. It has enough pressure to unseat the fuel gallery pressure regulator and return fuel to tank. Hardest part is plumbing it into the system before the lift pump.

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yeah its got a primer, i dont know if ive gone 200 pumps but i feel like ive had to be close to that. Do you feel no prime at all for the first 190 pumps? 

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You should feel it pumping 

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yeah, 300 pumps nothing. So i put some psi to the tank (20#) and it'll almost catch. I crack the return line at the front of the head and there's plenty of fuel there. But still no resistance at the primer. 

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If you were to

Just now, OJ Avery said:

yeah, 300 pumps nothing. So i put some psi to the tank (20#) and it'll almost catch. I crack the return line at the front of the head and there's plenty of fuel there. But still no resistance at the primer. 

Sounds as if the lift pump needs rebuilt. Either has a seal compromised or a valve no longer making a good seal internally.

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Got it to barely run at about 22# of air to the tank. I haven't ever seen a mechanical pump go bad. 

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It used to be common. Not so many are truly mechanical in operation any longer however as many use an electrical driven pump.

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Replaced mechanical pump, nothing. Put another filter head on it nothing. Replaced the line from the filter head to the back of the head (feed line) nothing. Filled the tank to the very top to check pickup, nothing. I'm going to do the feed and return from the tank now. The feed goes to a heater that's located in the frame rail by the trans. 

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Funny story... (NOT!!!) after replacing fuel filter head twice, replacing every fuel line, bypassing the heater, I come to find out someone at another location started the job, decided it was too much for their field location, slapped it back together and guess ...what it wouldn't run. They don't care its getting shipped off, not their problem anymore. I had no idea someone was already there. 2 lines got switched. I spent 66 hours on this ....SMH

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f**ksakes What a pain! So much for the flat rate hope you get paid by the hour!🙄

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I'm a state worker (NYSDOT).... I get paid by the year lol

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Made the same mistake misconnecting fuel lines on my '03 Golf TDI when I replaced the camshaft drive belt- Stumped me for awhile as it would start and run for a few seconds and then die. Got some online help from the forums and 8 years later the baby diesel still runs strong!

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35 minutes ago, Maxidyne said:

Made the same mistake misconnecting fuel lines on my '03 Golf TDI when I replaced the camshaft drive belt- Stumped me for awhile as it would start and run for a few seconds and then die. Got some online help from the forums and 8 years later the baby diesel still runs strong!

Those were some good ones for sure. Good starters in the cold and delivered very good economy.

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