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Old 11-18-2000, 02:50 PM
Posts: n/a
My 300D is suffering from an apparent lack of fuel at 2900 rpm+. The car starts, runs and drives just fine, shifts well etc. but just when it should be starting to get some serious boost, (~2900-3000 rpm), it stops accelerating and just flattens out.

I have changed main and inline fuel filters. Additionally, I cleaned out the banjo nut and lines on the back of the intake manifold and the pressure switch (both were plugged).

What am I missing? Many thank for the insights.

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Old 11-18-2000, 04:54 PM
Wm. Lewallen
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A few things you might check:
Throttle linkage; Check to make sure it is up against the stop on the pump when the pedal is fully depressed. (assuming it has not been set for slower speeds).
Check fuel pump delivery. I don't have the specs at hand but if you don't have them, I could look them up and send them to you.
Good luck to you.
Bill Lewallen
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Old 11-18-2000, 05:32 PM
Posts: n/a
I would suggest that you do a search on this forum for turbo boost adjustment. There is a line that goes from the turbo or the output of the turbo to the injection pump which somehow adds fuel delivery when boost is achieved. There is an adjustment and some other things that need to be checked.

I expect that this is where your problem can be found.

Good luck,

Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles
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Old 11-19-2000, 08:11 AM
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Not likely, but I would also check the screen in the outlet of the fuel tank. It is eay to do, especially when you have run the tank to almost empty. When I did mine, I used an old refridgerator drawer (white enamel) to catch the fluid and have a visual inspection. This would be a good thing for yor car, even if it was not the root cause. Good luck.

87 300TD, 160,000 miles
72 280SEL 4.5, 250,000 miles
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Old 11-19-2000, 01:41 PM
R Easley
Posts: n/a
Good afternoon, John --

You don't say in your post whether you _initially_ had the problems that you are describing or _after_ you did the procedures described.

If the problem happened _after_ you changed filters, I would guess that you may be pulling air at your primer pump. Either the pump knob was not securely closed or it may be leaking anyway. It's always a good idea with the 617s to keep a spare for this very reason (not to mention that the primer pump may stop working at the precise time that you really need it!). Even if your problem was being evidenced before you started working on the car, it still may be the primer pump. I would check this first.

On the turbo boost adjustment procedures, the procedures for checking the boost sensing lines and checking and adjusting boost pressures can be found on my site at:

Note that I would _not_ recommend adjusting your own boost unless you are a confident, very competent DIYer. On the other hand, if you do fit the above criteria, I would not hesitate to do the adjustments. You will find the results most pleasing, with no reduction in the reliability of the 617 engine, but dramatic differences in the performance of your car. Adjusting the boost to proper levels (and within MB specs) is a procedure that will significantly benefit probably 99% of the 617-equipped MBs on the road, yet virtually no one was talking about it until Stu Ritter (Technical Editor of The Star, MBCA's club magazine) alerted me and other DIYers to its advantages about 5-6 years ago. What is most surprising to me about the procedure is that I believe that many MB techs do not even realize that is possible to do. For example, about 3 years ago I was talking to one of the most senior MB techs at one of the largest dealerships in the southwest about turbos and performance adjustments/modifications. Not only did he work in the dealership, but he also owned a 617-equipped MB. And, though this sounds illogical, he said that the shop had regularly (and frequently) replaced turbos in the past for inadequate boost, not knowing that they could be adjusted.

Richard Easley
Waco, Texas
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Old 11-19-2000, 04:12 PM
Posts: n/a
Thanks for all of the excellent insights, gentlemen. I dug into this because after changing the fuel filters, the car wasn't building any power. As a result of my online research this weekend, I've fixed several vacuum leaks, vastly improved shift performance, cleaned out the boost sensor line, tested boost pressure, etc. I am certain that I wasn't getting any boost before this weekend, just due to boost lines and banjos being plugged.

I still have a serious smoking and power problem. More insights: It starts well hot and cold (25 degrees this morning without being plugged in) and idles very well. The power is good up to 2500 rpm and then it goes soft.

The entire fuel system is dry and without any apparent leaks. When I replaced the spin-on fuel filter, I installed a NAPA Gold and filled it with Redline before installing it. I didn't disturb the hand pump... I just started the car and it roared to life. Everything is dry so I don't believe that I have any leaks.

BTW, the smoke is whitish gray and is more visible the farther I drive the car i.e. it is ok on my street, but 1 mile away it gets worse. (This on an already warm engine.) Any ideas? Many thanks for all of your help.


82 300D
90 Volvo 760T
88 Volvo 745 256000 miles!
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Old 11-19-2000, 06:47 PM
Posts: n/a
***Great Idea***
I read an archived post somewhere that symptoms like this could be the fuel overflow valve. Does anyone want to offer an opinion?
Many thanks. You folks are great.
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