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Old 04-07-2009, 08:58 AM   #1
Join Date: Nov 2006
Location: New Jersey Shore
Posts: 36
Fuel Contamination Problem

Our 1999 Monaco Windsor has a Cummins ISC engine. The coach had sat for a year before we bought it. I had the coach serviced and checked out before driving it from Florida to New Jersey. As part of the service, all fuel filters were changed. The engine ran great until Virginia. While on I295 around Richmond, I was cruising along at 65 MPH. While rolling up a hill, the engine started to miss. After cresting the hill, everything was okay again. The next hill, same thing happened, only worse. I backed off to 55 MPH to see what would happen and everything ran good again, even going up and over the large bridge over the James River. Shortly after, the same miss came back. I even had the "Stop Engine" light on the dash come on. This worried me as I wasn't sure if this meant that I should immediately pull over and shut it off or not (did I tell you I'm a rookie when it comes to diesel engines?).

When that light came on, I pulled over to the shoulder and stopped. The light went out so I left the engine running. I called the dealer in Florida and asked the service tech about what I was experiencing and what if I could do any damage running the engine when the engine stop light came on. He told me not to worry about it, that that light was showing some sort of "conflict" and that I would be okay. He suggested finding a truck stop as a lot of times, you can find a diesel service center at the truck stop. I didn't know where the next truck stop was but figured since I was in the Richmond area, I could probably find someone in the area.

I ended up finding a Cummins Service Center. They determined that I had contamination in the fuel and showed me the fuel that came out of the primary filter (the one with the water separator on the bottom). There appeared to be a lot of black (dark) particles in the fuel. The Cummins Service Center ended up replacing the first two filters (three filter system) and gave me an additional primary filter to take with me in case the problem started up again.

I made it home without any further major incident. I did feel an occasional miss, but a lot less severe than the original problem. The biggest difference I noticed was less acceleration. Prior to the problem arising, when I pressed down on the accelerator, I had good acceleration. After the problem, I could still get up to 65 MPH but the acceleration was a lot slower, although steady.

Sorry this is so long.

What I'm asking is for suggestions on what I should do next. Should I get a sample of the fuel and send it off (where to?) to get analyzed. Do I simply bite the bullet and have the tank drained and dispose of the fuel, clean the tank and start fresh? Someone told me of a "bug" that feeds on diesel fuel and leaves its waste behind. Is this the black "stuff" I saw in the fuel? That same person told me of a Stanadyne product that will kill the "bug" and get rid of it if that is the problem. Another person suggested using Lucas diesel fuel additive.

I should also add that I was only getting about 6 MPG on the drive North. Does this seem low? I was expecting something in the neighborhood of 8 to 12 depending on any headwinds and terrain. Is this probably caused by the fuel which caused my other problem?

We have a trip to Yellowstone planned in two months and I would like to have all of this behind me before I leave. Thanks in advance for any and all suggestions.

Bryan and Lee - Retired Firefighter and Banker
Proud Parents of a US Marine
1999 Monaco Windsor 38' Suite Slide FD
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Old 04-07-2009, 10:08 AM   #2
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Join Date: May 2008
Location: Washington
Posts: 101
What you have is called black algae. It forms in the fuel tanks of diesel powered equipment ( boats, trucks, RV's Etc) when condensation forms in the tanks when left less tan full for a long period of time. An additive to the fuel should take care of your problem but carry lots of spare fuel filters. As the algae dies and the sloshing fuel releases it from your tank walls it goes right into your fuel system. In extreme cases your tanks and fuel may need to be scrubbed.
Tom and Sue
2005 Alpine FDQS
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Old 04-07-2009, 12:24 PM   #3
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Is the algae basically a warm climate problem or could it also grow in a tank that was less than full and stored for the winter in a cold climate?
Bob Russo
Formerly had 07 Neptune 36PDQ, ISB 325, Allison 2500, Source Trailing Arms and Ride Enhancement Kit, Demco KarKaddy 460SS.
Currently no Motorhome
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Old 04-07-2009, 03:03 PM   #4
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Don't know I had this problem with my boat in Seattle. I think it can grow when ever condensation forms which would require a change in temp
Tom and Sue
2005 Alpine FDQS
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Old 04-07-2009, 03:40 PM   #5
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Algae in diesel fuel usually grows in a boundary layer between diesel and water. So you probably have two problems, water AND algae. The water most likely came from condensation. You CAN kill the algae and minimize future problems by adding a biocide, BUT you will still have dead algae (looks like black slime in your filters) in your tank. And the dead ones clog your filters just as good (or bad) as the live ones. The diesel in your tank most likely is still good once the water and bugs are removed.

There was a service I used once for my boat where they would "polish" my fuel by pumping my existing diesel out, pressure clean the tank, filter the fuel (using their filters, not mine), then pump it back in the tank. Maybe you could find a service like that for your rig? I don't recall it being terribly expensive.

The best way to prevent condensation in the tank is to keep it as full as possible any time the rig sits idle for more than a few days.

If you address the cause of the problem by limiting condensation and using a biocide, going forward, the fuel quality in the tank will slowly improve. It may take several fuel filter changes though.
Brian & Missy
1998 American Eagle, Cummins C8.3
2002 Envoy Toad, SMI AFO aux. brake
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Old 04-07-2009, 03:46 PM   #6
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treating it and replacing filters will solve present problem..shame when first serviced they didn't drain the tank..once clean keeping a full fill up when around half empty, buying fuel at stations that pump a lot of fuel so its hopefully always fresh, and putting a good anti algae/anti gel into the fuel before putting to bed for the winter will solve most problems..
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