Vito 638 112CDI Fuel draining back to tank.

Bunnyboy

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Any words of wisdom on where to start?

My Vito 638 112CDi 2002 has developed a problem starting some mornings. Starts fine once been running.
The fuel filter has an air bubble that appears in one of the lines after a few minutes of engine stop and slowly grows. The filter has three pipes at the top and its the far left looking from the front of vehicle which I believe brings fuel from the tank.

Cannot see fuel in the clear pipes when engine running.

Taken to the Merc dealer and they changed fuel filter thinking they had solved the problem. Unfortunately it hasn't, possibly slightly worse.

My question where to logically start.

Purchased O rings to replace seals at ends of fuel lines. Common problem with this engine but some hard to reach.

Purchased T valve top of fuel filter that I think has something to do with heated fuel.

Bit apprehensive to change O rings and T valve in case of introducing too much air into system and not being able to start again. Is a priming pump required before even attempting?

Other possibilities that could be cause as far as I can deduce are:
injector leak of pipes and their clips
Water drain valve on fuel filter, but assume new one with filter.
Water sensor O rings. Mercs didn't appear to put on any new seal when replacing filter unless supplied with filter.
Fuel pressure regulator seals. Believe this normally would cause problem starting when warm if gone.

Booked back in with Mercs in New Year but would like to have solved or at least have a logical (less expensive) route to solve issue.
 

LostKiwi

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Fuel can only drain back if something else is there to replace it. It sounds like leaking O rings.
 
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Bunnyboy

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Further air introduced disconnecting fuel lines

Yes they do seem to be a weak link. Some hard to get to without removing engine mount etc. Any idea if I will need to use priming pump if I replace at least the easy to get to one's.
 
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Bunnyboy

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Anyone had seen this before. Clear inlet fuel pipe seems to drain back towards tank for about 3 inches. Pipe will fill with fuel once started but starts to drain back after about 5 minutes once switched off. Van back with Merc dealer for the third time. New fuel filter fitted (filter with water sensor). New outlet fuel pipe fitted that goes to the high pressure pump. Several new O rings fitted, not sure which ones but the problem persists. Cost me more than the vans worth so far so any advice would be welcome.
Is it possible its:
The T shaped valve that also sits on top of the filter
Rubber fuel hoses
Water drain valve (Assume seals etc. came with new filter)
Pressure regulator seals
Injector leak off pipes.

Anyone?
 


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