1997 W210 606 Fuel Flow Mod..
 

Hi. I have just finished rebuilding a 606. Have had problems over the years getting 'air' out of the fuel system.

I imagine most diesel Mercedes have similar small bore fuel tank outlet inner id.
This one proved a little more problematic than usual in the fuel department.

On the 606 the i/p pump is larger, pumps more volume. Until this pump, the earlier i/p's pulled fuel too but the 606 pump really sucks. I wasn't getting the engine to rev up like I knew it could so I checked fuel delivery .

Zero air leaks but small vapor bubbles at 4000 rpm . Checked and rechecked and no air leaks anywhere. This may have been covered but it appears that diesel will boil off vapor if sucked on hard. Ergo: Bubbles in the fuel lines and rough running engine. Bubbles will not collapse back into fuel again though.

I thought about a 12 vdc pusher pump near the tank but that introduced another 'weak link' plus is would be subject to unfiltered fuel and new owner wants to run 50/50 wvo to diesel.

I pulled the strainer out of the tank and found 1/2 inch of black sludge and 50% restricted tank strainer. Also the outlet fitting was very small...about 6 to 7 mm into the flex fuel hose. Couples with the 6mm flex hose restriction it seemed too small especially considering the long steel fuel line to the fuel pump.

So, I drilled out the tank strainer to just smaller than the threads for the outlet hose. Discarded the OE flex hose and found a 12mm silicone hose to marry the now 12mm outlet with a 1/2 barb fitting screwed into the tank strainer outlet.

Now have no bubbles now even at 5500 rpm and engine ramps up smartly to 5k..

So if you having reduced power in your 606, look to opening up the tank strainer.

I also squeezed the blanking ball in the i/p relief banjo in just a hair and found 8 psi blow off now, instead of 4 psi before, with a pressure fitting test. Should they test higher ?( FYI : Early W123 and 126 relief valves are smaller thread. So no super duper relief valves for 606's.)



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Nice work.

The relief valve should be in that ball park, maybe 8-10 psi. Having a higher pressure helps refill the elements as they open up. At high speed, the higher pressure is needed to ensure the whole element fills up before the port is closed off and the fuel is injected.

If your tank strainer was blocked, you might consider treating your tank with a biocide like startron and a fuel system cleaner.

Yes...Getting bio-cide from O'Riellys. About $8.00 to treat a tank of fuel.

He's going to add a bottle every tank for 5 tanks and change fuel filter every thousand miles for next 5k.

Looked at installing Racor but unit too big to fit near tank outlet.

Seeing a lot of Ford F series with 6.0 engines having injectors killed due to poor quality low ULSD fuels. The 500 plus ppm sulfur fuels used to kill the bacteria.

On the trucks we can install a Racor on the frame rail before the HFCM. ( Horizontal Fuel Conditioning Module. )


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If you have concerns about fuel quality, a bit of 2 stroke oil will increase the lubricity quite a bit. For lubricity and cetane boost, you can use some Power Service or mix the two. As always, filling from high volume stations and ones that are nicely maintained is important in avoiding bad fuel. The biocide should clean the tank up nicely.

You properly identified the problem of the clogged tank screen as being the issue.

Otherwise the ID of the hoses and tubings are entirly OK. A large amount of Fuel passes through the Fuel Injection Pump to cool it and very little of that gets injected into the Engine.

But, the Fuel Pressure inside of the Fuel Injection Pump Housing has to be within certain limints or it will not pass fast enough to get inside of the Elements.

That is where clogged Tank Screens and Fuel Filters cause issues as well as the Fuel Supply/Lift Pump (may need a rebuild kit) and the Fuel Pressure Relief/Overflow Valve (has a plastic piece in it that warps or falls apart) may not be preforming well either.

There is 2 threads on rebuilding the 603 and 606 type Fuel Supply/Lift Pumps with new Valves and O-rings.
If the Fuel Pressure Relief/Overflow Valve plastic part is messed up people have been replacing it.

Thank you Diesel911. I think a new O/V is in order though. I found a paper on the www about how diesel fuel will form non coalescing bubbles when subject to negative pressure...vacuum.

As the elements in the I/P operate, it is quiet possible vapor bubbles will form as they try to fill at high rpm's. Another reason Bosch went to 'common rail'.


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Have you had any experience with 2 Stroke Oils added to diesel fuel manny ?
Owner of this W210 is in OKC so has several diesel stations with high fuel turnover to use.

He's dosing the tank with a biocide for next 5k.

Will 2 Stroke increase cetane though ?


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Yes I have. I used to add 2 stroke oil with every fill up because I was worried about lubricity. I fill up at Shell and Chevron stations exclusively, and "my" station is well maintained. Since the fuel I use contains biodiesel, I no longer add the 2 stroke oil. I add Power Service white bottle after Thanksgiving when temperatures start to get around freezing, as insurance against fuel thickening and gelling.

2 stroke oil will raise the cetane of the fuel, but a dedicated cetane booster will be more suited for the task. Back when I used to use 2 stroke oil, in the winter I'd measure out a dose of 2 stroke oil, a dose of antigel, and put both of them in an empty (cleaned and dried) 16 ounce soda bottle. When I filled up, I'd pop the trunk, pour in a bottle, fill the tank, and go.