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Old 08-31-2014, 03:13 PM
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Any OM603 diesel injection experts on the list?

My 350SDL runs very good, but not as good as when I first got it. I never had a diesel run so smooth. Now there is a slight vibration at idle.

I had noticed that the pass through fuel filter looked like it had dark fuel in it and suspected a dirty fuel tank. All the injectors are fairly new and the injection pump is fairly new and the turbo unit have been rebuilt. I did not notice if the darker fuel came before or after the rougher idle.

Even though the injectors an pump were pretty new, I decided to do a diesel purge. The purging fluid is a clear amber color. When I disconnected the fule line from the tank to the filter, I allowed a little to go into a plastic container so I could look at the fuel coming from the tank. It looked more of a darker green than the normally slightly greenish but clear diesel fuel, so I figured my tank was messed up. Worst case, I thought I might clean up any carbon buildup in the cylinders.

I Took my fuel return line and a fuel delivery line and set them in my purging bottle and filled it with the purging liquid. The delivery line from the bottle went into the inline fuel filter.

Almost immediately on startup, the fuel filter got much darker. The fuel tank was not dirty... Oil was being mixed into the fuel and then being sent back into the tank. Upon running, the car had no extra dark exhaust or anything that leads me to believe that the cylinders were dirty. The car always ran well. The bottle with the purging liquid became dark very quickly. This never happened before whenever I have done a purge.

So my question is, how can oil be getting mixed into the fuel between the time it goes into the pump and then comes back into the return line. Even if the turbo was shooting oil back into the car, I don;t see a way for it to get into the fuel and the exhaust is not dark enough to give me the feeling that it is burning lots of extra oil (although it must be burning some extra through the fuel).

Do I have an internal problem with the injection pump, and can it be fixed without taking it out? Or can something else be causing the oil to mix with the fuel?

Thanks

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Old 08-31-2014, 06:46 PM
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Join Date: Aug 2013
Location: Tucson, AZ
Posts: 1,251
The lift pump.

Rebuild/replace the seals inside it.

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