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Old 05-24-2021, 09:48 PM   #1
Skoolie
 
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Join Date: Oct 2017
Location: Bellingham Washington
Posts: 129
Year: 2005
Coachwork: Thomas
Chassis: Freightliner
Engine: 6.4 liter Mercedes MBE 900
Rated Cap: 48 passenger
Fuel Hose Deterioration?

Hello all,
I have black specks (particles) in my engine pre-filter housing. Symptom: engine cranks well, but doesn't start.

2005 Freightliner/Thomas dognose with a MBE 906.

After talking with a service guy at a Freightliner shop, he told me it is likely the fuel hoses that are deteriorating. The "crud" does seem more like rubber bits than fungus.

And, to me, the fact that they are in the engine pre-filter housing means that if they came from the tank, the bits had to pass through the fuel/water separator filter. Is there not at least some kind of particle filter in a fuel/water separator? I would think even a screen would take out this stuff.

My theory for why the engine will not start is that the crud has prevented the check ball at the bottom of the pre-filter housing from seating, allowing fuel to drain out and losing prime. There is not enough debris to clog the filters, not even the pre-filter screen.

So... my questions are:

Does it seem likely that the black particles are coming from deteriorating hoses in between the water separator and the engine filters?

Would you replace just those hoses, and all the filters?

Until it wouldn't start 2 days ago, It has started easily and run beautifully, though I haven't driven it much - 2020, Covid, recovering from a stroke a year ago - only 3000 miles since summer of 2017. My build is almost done, and I'm ready to go somewhere.

What do you think? Y'all know way more than me.

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Old 05-25-2021, 06:10 AM   #2
Bus Geek
 
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Join Date: Dec 2015
Location: pa
Posts: 2,519
Year: 98
Coachwork: 1. Corbeil & 2. Thomas
Chassis: 1 ford 1998 e350 4x4 7.3 2 mercedes 2004
Engine: 7.3 powerstroke & MBE906
I had similar problems with our mbe906.
No start, loosing prime.

In our case...the fuel pump on the engine had a failed overpressure bypass valve allowing fuel to drain back.
It was a rubber flap/ membrane valve and I could not fine the individual part.
Somewhere in the beginning of our built thread are fotos and repair discussion.

Good luck.
Johan
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Old 05-25-2021, 07:54 AM   #3
Skoolie
 
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Join Date: Oct 2017
Location: Bellingham Washington
Posts: 129
Year: 2005
Coachwork: Thomas
Chassis: Freightliner
Engine: 6.4 liter Mercedes MBE 900
Rated Cap: 48 passenger
Thank you, Johan.
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