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Diesel draining back to tank when parked up over night.

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Hi All,

Im new on the page but have had looks at it over the years. I've recently brought a 1990 Mack RB688RST NZ model, its got a E6 350 2 valve in it and it keeps draining the fuel back to tank over night. I've attached a few photos of it and the fuel system, It has 2 primer pumps on it, 1 in behind the primary fuel filter which I've replaced the copper washer under it and the oring and it was good and now its starting to drain back over night again. Has anyone else had the same sort of problem in the past?? any help wou;d be much appreciated.


Kind Regards 

rb mack 3.jpeg

rb mack.jpeg

rb mack 2.jpeg

rb mack 4.jpeg

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Welcome to the forum!

 A clear fuel line can be used to test if you have air coming in through the primary side. Could be a check valve in the system but I cannot say for sure. Definitely check all the return lines too.

You said it was a 2 valve? In America the 2 valves were mostly fazed out by 1986 but maybe it's different elsewhere. Nice looking truck either way 

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Hi paul and bob, I’ll check the return side in the weekend thanks, it’s getting to be abit of a pain in the ass when it won’t fire straight up the next morning. Yeah its a 2 valve hasn’t got the angled rocker covers and looks identical to my old E6 320 that was 20 years older. We are a little bit further south so we obviously got the last of the 2 valves being at the end of the chain 😂😂

Edited by Mackman686
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I would be suspicious of the line returning to the front injector at the front there! That is Not exactly stock looking! and all the jumper lines between the injectors! be sure they are not damp any where! 

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