OM606 air in fuel lines - worse after filter change - PeachParts Mercedes-Benz Forum

E_S · #1 09-30-2019, 10:37 AM

OM606 engine. Replaced the fuel filter. Noticed that the previous owner had replaced the filter bolt with the stop knob with the old-fashioned regular banjo bolt.

Air was present in the fuel lines before replacing the fuel filter, but after replacing, it got way worse. Now the car hesitates to start and idle after sitting a couple hours (fuel will drain back) and performance is low.

Check out the video to see the two lines with the most air. The other lines are either without air or just a couple very tiny bubbles. The lines between the fuel filter bracket and the small pump mounted on the injection pump are the "leaky" ones.

When I replaced the filter, I did not touch any of the fuel lines, only the fuel filter bolt. I have replaces many of those filters before and never had any issues, so I'm pretty confident about that process.

I will replace all the O-rings anyway, as they are probably 25 years old, but would like to track down this problem first, as it got worse after replacing the filter.

Will using the old-style filter bolt make any difference except that you lose the stop-function? I see that the original bolt has got two O-rings while the one I have installed only have one..

Video of air in fuel lines

spock505 · #2 09-30-2019, 01:48 PM

Those two pipes are from the pump, its drawing air either at the pump (O rings) or before - check fuel strainer located under tank, also vent to make sure tank can breath.

Go from there.

E_S · #3 09-30-2019, 04:46 PM

Tank is venting, that's for sure - because the filler neck has developed a tiny rust hole. Will replace the whole tank next week.

It seems strange that the O-rings suddenly got bad - but what I did do last weekend was fixing a rust hole, where I saw that the two fuel lines from/to the tank looked pretty "crusty" right where they bend down from the rear suspension area to under the car. I had to take those loose, and bending/moving might have caused a tiny crack in the rusted out part, maybe/probably.

After replacing the fuel filter, it took way more cranking to restart the engine than it usually does as well.

Of course I will replace the O-rings - they are 25 years old and probably not good, but I just try to track down what caused this problem to suddenly appear.

If I'm right, the fuel flows from the tank to the strainer in the filter bracket, then to the small pump, then from there to the main filter, and from there to the injection pump? Which should, as you say, make it pretty clear that the air leak is either at the tank, the lines, the strainer or the pump?

The "wrong" fuel filter bolt can't have anything to do with this air?

spock505 · #4 09-30-2019, 04:59 PM

Not sure what you mean by filter bracket, the strainer is located directly under the tank.

The plastic pipes are so rigid any movement will disturb O rings, even if just pushed out of way.

E_S · #5 10-03-2019, 01:28 PM

I was thinking about the pre-filter in the filter bracket. It's just a tiny strainer, not a "real" filter.

I ordered and got all the O-rings new today, will have a look tomorrow and try to replace them. Seems pretty tight - hope to be able to do it without taking the intake off the engine..

E_S · #6 10-05-2019, 01:40 PM

Replaced all O-rings today. Culprit was the line between the fuel heater '(?) under the intake manifold and the filter bracket. Once this was replaced, all bubbles disappeared and it's all good again!