Hi,

1990, 300D 2.5 Turbo, 130K.

Problem is poor acceleration (especially at higher speeds - anything over 30MPH) and significant power loss (acting like its a 90HP motor or something) - very sluggish. Normal behaviour otherwise. Occured fairly suddenly within space of 2-3 weeks, I have had car for 2 years with no similar problem. Acting like engine is starved for fuel, and turbo kick seems to be gone.

No smoke at any throttle, engine runs cool, normal fuel consumption.

I have tried changing out both inline and screw on fuel filters, tried blowing the line with air to the tank, turbo is fine, have tested vacuum system around turbo and air-intake (including all three valves - EGR, waste gate and that other one - these are all fine). Throttle linkage is good. Air filter clean. Vacuum is developed from system at the valves around turbo.

What else could it be?
- Could it be seals in the fuel pump - can't develop enough pressure (rebuild necessary)?
- Something around the fuel pump (ALDA or boost pressure to aneroid)?

Thanks, I'm pretty lost by what this could be. Any suggestions greatly welcomed.

mike

You most likely have a plugged boost line to the ALDA. The ALDA is the flat square box on top of your injection pump. There is a translucent line going from it to an overboost protection switch and then to your intake manifold. you should be able to blow through the line from the ALDA end back to the intake(with the engine off please). The most common spot is the banjo fitting at the intake end. The other likely spot is the switch with no power to it you should be able to blow air through. Carb cleaner works well or WD40 in a pinch. Mind that you don't lose the two washers on the banjo fitting or snap the line. It can get brittle, but can be patched with rubber hose until you can replace it. If your EGR were to some how become disabled by a BB falling accidently into its vacuum line this might occur less often.

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Bob D.
Parrish, FL
1 SDL, 1 D, 1 TD, 1 Mog

Try this, it worked on mine when I had the same problems.

http://www.mindspring.com/~houlihan/merc/banjo.htm

I tried cleaning out the banjo fitting - there was a lot of gunk and stuff in there so I cleaned it out. After I reconnected everything car is still behaving the same.

When I disconnect the pressure hoses, I am able to blow air from ALDA to bottom of that blue vacuum pressure thing (looks like a little flying saucer with hosts coming out from top and bottom) on the far driver's side (in front of the boost pressure overprotection), but not through the blue thing. I can also blow air (although poorly) from the intake manifold (banjo fitting) to the blue thing, but again not through it. - SHoudl I be able to blow air through it?

What else to check next? What about that ALDA adjustment?

Thanks for the help so far guys,
Mike

You do not want air to blow through that blue thing - that is the vacuum modulator for the tranny. Just worry about from the intake manifold to the Alda at the injection pump. Did you totally remove the banjo fitting to clean it out. You need to insure that it is clean all the way down into the manifold.

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Jim

Mike,
I have to say I've never had my hand on a 90 2.5 turbo, but boost pressure has to reach the ALDA or you will not get any extra fuel to go with the extra air the turbo is making. you won't do any harm spraying WD40 down the boost sensing line from the banjo toward the ALDA and using some compressed air with the line off at the ALDA end until you get flow. With no boost getting to the ALDA you are driving a non turbo 2.5. If you're feeling adventurous you might Tee in a line at the ALDA end and run it temporarily into the cabin and put a pressure gauge on it.

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Bob D.
Parrish, FL
1 SDL, 1 D, 1 TD, 1 Mog

One more thought, you might try running a line directly from the banjo to the ALDA and do a test drive I bet you'll like the results. Afterwards though you need to restore what ever additional over boost protection the wise MB engineers provided (The waste gate on the turbo will keep you well within safe limits). On the cars I see most often there is a simple solenoid switch that is in the line to the ALDA. It is connected to a pressure switch on the intake and vents excess pressure before it reaches the ALDA in the event of waste gate malfunction. I don't know if this is incorporated into your blue box.

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Bob D.
Parrish, FL
1 SDL, 1 D, 1 TD, 1 Mog

I didn't quit follow h20's directions completely - or maybe I refered to another post regarding the ALDA.

The banjo was cleaned out fine, and the tubes were okay but when I tried blowing air from the ALDA to the intake manifold (through the switchover valve aka overboost pressure switch) it was completely blocked.

My dad has a 1991 300D 2.5 (same thing practically), and I found I could blow air fine between the ALDA and the intake manifold. I took off and cleaned the overboost pressure switch and VOILA -- turbo up the ying-yang.

You just don't know how much you will miss the turbo boost until you don't got it.

btw h20diesel, if you are ever around edmonton, canada I owe you a beer.

thanks again guys,
mike

lol - I forgot about the overboost protection switch. I removed the one on my 300D a few months ago.

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Jim