I just purchased a 1987 Mercedes 300D, the car has 136,000 miles and has good service history. As it’s my first diesel the acceleration when tested seemed normal for a diesel, (slow) until I test-drove my neighbor’s 1981 300D, this was a rocket compared to mine. I found that mine had the oxidizer trap which the MB dealer removed with the recall retrofit. This made a significant difference but still seemed slow. I noticed that the intake manifold had build up of oil; this was cleaned at a machine shop and made a difference but still slow climbing hills. The car was always driven at sea level until now I live on a hill at 2400 feet ASL, I should mention that the valley is at 1100 feet ASL and its fairly steep climb. The car starts first crank every time, after the initial bit of smoke and roughness, the exhaust comes out very clear and idles smoothly. My question is, is there an adjustment and or a mechanism that compensates for the altitude. On flat road at 60MPH the car cruises at 2200 RPM. There is a noticeable difference in acceleration above 3000RPM, but getting there is slow. Climbing hills is very slow, any suggestions.

Try reposting this in "Diesel Discussion". I can give you a few suggestions though:

1. Check all vacuum lines under the hood, make sure they aren't clogged and or broken.

2. See that 5 way vaccum fitting at the front of the engine? Replace it with a 3 way - which disables all the stuff on the passenger side of the engine compartment.

3. Make sure the turbo spins freely and is generating the right amount of boost.

4. The device you mention is the ALDA - it is under the intake manifold and sits on top of the injection pump. Make sure the plastic lines going to it are not leaking (and also that the unit itself holds some vacuum).

Lastly, this car is FAST for a diesel. It should blow away any of the older Mercedes diesels, especially that 1981 300D!

If the intake system is as gunked up as you claim, it's possible that there's gunk in the line between the intake manifold and the ALDA which is the device that tells the injection pump to add fuel because the turbo is pressurzing the system. If there's no additional fuel, the turbo's boost is inconsequential.

There's a line that goes from the intake manifold to a small black device (overboost swtichover valve) on the firewall, then from the valve to the ALDA unit atop the injection pump.

Clean both lines and see if there's an improvement. If not, don't worry, there's more to check.

TEMPORARILY bypass the overboost switchover valve. Don't run it with the pedal to the floor but run it hard enough to see if there's an improvement. If there's an improvement, then clean the valve. It should be safe to spray brake parts cleaner through the valve, but take that advise with a grain of salt. The valve is open when unpowered.

Hopefully that's it. If not, attach a pressure/boost gauge to a tee fitting in the line between the intake manifold and the valve and repeat with the gauge tee'd in between the valve and the ALDA. See how much boost you see with the car on the road. The turbo doesn't make boost without a load. You should see boost kick in around 2500rpm and a max of something like 12psi. This should tell you something about the health of the turbo. If you see boost before the valve and none after the valve, it could be that the pressure sensor beside the intake manifold fitting is stuck.

I hope this helps.

Sixto
91 300SE
87 300SDL
83 300SD

Thanks for the prompt reply, the turbo has been checked and is fine. I will perform the other checks next week. I appreciate you walking me thru this, I may have more questions next week. Cheers!

Gentlemen: Thanks for your suggestions. You were bang on about the line from intake manifold to the ALDA possibily being plugged and cause of the loss of power. I had that line cleaned out, the ALDA tweaked, boost pressure checked. Now the car accelerates 0 to 60 in 10 secs.