Sluggish 85 300sd - PeachParts Mercedes-Benz Forum

#1 08-01-2002, 07:24 AM

My 1985 300SD is extremely sluggish. In the past, this was eleviated by idling the car for 15 minutes or so before driving. But now, even this doesn't seem to work. Even with the accelerator floored, the car barely reaches 30 miles per hour up hill, hitting 3500 rpm before it shifts gears. Lately the heat and humidity has been high which could be the problem. Any suggestions?

mbdoc · #2 08-01-2002, 08:11 AM

ALL diesel engines need FUEL & AIR, so have the filters been replaced lately? The fuel filter can cause all kinds of problems, try a new one before spending too much $$$$.

downeyjc · #3 08-01-2002, 03:52 PM

Sounds like a vacuum leak to me, especially since your transmission shift point has changed--it requires a specific vacuum to work correctly. You should look carefully at all of the small vacuum lines and connections in the engine bay. There are several "multi-connectors" in the vicinity of the fuse box where one line branches out into 3 or 4 different lines. These connectors develop cracks that are evident when when you look closely at the branching point.

I've had so many instances like yours, that I eventually bought 10 feet of vacuum line and replaced every line that I could find on my 300SD. Haven't had a problem since then--though still carry some spare line in the trunck. I'm always shocked at how much of an impact that a small leak has on a diesel engine. Fix it and your power will go WAY UP. Good luck. John Downey

Billybob · #4 08-01-2002, 04:06 PM

Sounds like a restricted or blocked boost signal from the manifold to the ALDA. When the turbo starts pumping more air more fuel is needed, without the boost signal the engine does not getthe proportionally more fuel that it needs. The result is like having a normally aspirated diesel! Pretty slow sluggish behavior especially a lack of acceleration under load.

Disconnect the hose from the manifold or IP and if there is no difference, that is probably the problem. The cure is cleaning the accumulated carbon/oil from the fittings, hose, and overboost switch. A good signal to the ALDA will result in the characteristic surge of power when the turbo spools up around 2000 RPMs, hang on! Good Luck!