92 300d 2.5 turbo poor performance - PeachParts Mercedes-Benz Forum

rlm · #1 05-21-2007, 10:17 PM

Competent part-time mechanic, new to the site. I just purchased a 92 300d with 200k. I had several VW diesels in the past, but am not very familiar with MB diesel. The car is a dog. If I power brake it wot, it takes a few seconds to get past idle and after a few more seconds I can hear the turbo spool up slightly and eventually one of the rear tires will overpower the brakes (barely, on gravel). I don't expect a fast vehicle, but based on my past MB diesel driving experience (82 300SD), and mechanical knowledge, something is wrong. Loaded question, but where do I begin. Bad tubo? Clogged exhaust? What does alda stand for? I think I need to check boost for starters...........Any help / suggestions appreciated.

Bio300TDTdriver · #2 05-21-2007, 10:41 PM

Try reading this thread. Need Help Tons of Black Smoke 91 300d

You can also you the search function. I would start by cleaning the vacuum line and fitting that come of the intake manifold. New air and fuel filters. Then do a search on plugging the EGR.

This thread should help too. 87 300D Turbo not working

Chris

asantoni · #3 05-22-2007, 08:17 AM

I have a 92 300D 2.5T that had the same issues when I bought it. The first thing I would recommend is installing a boost gauge to see what the turbo is doing and when. You should be building boost by 1800-2000 rpm and holding 11-12 psi steady all the way up to redline. The wastegate on these cars is backwards from other turbos. It uses vaccum to hold close the waste gate and as boost builds off it bleeds off vaccum and starts to open the waste gate. No vaccum no boost. If the computer detects any type of errors it will also shut off vacuum to the turbo. I had several issues with the ALDA being clogged and thus not delivering enough fuel for further boost to build. Do a search for ALDA on these cars and you'll find tons of info on it. These are truly great cars and where considered some of the fastest diesels for their time. Once you work through all the vacuum related problems you'll have a nice car with a solid diesel engine. We average 30 MPG mixed driving with the air on. Good luck.

BigBen · #4 05-22-2007, 10:17 AM

rlm,

First of all, Boost Gage.

Then, have a look at my recent work on a similar problem:

EDS Codes on 1992 300D 2,5 Turbo

Now that I do have decent boost, I noticed just this week end that my EGR is leaking (shows black soot or oil thrown at good velocity on valve cover). So I'll have to investigate a little more on this side and on the ALDA as well...

Good luck,

Bye

Dana B. · #5 05-22-2007, 10:48 AM

Be sure to check your overboost protection valve/switch. Mine gave me trouble for a year. They get plugged up with soot. Unplugged it, problem solved.

gsxr · #6 05-22-2007, 02:40 PM

My 1993 300D was also sluggish when I bought it. Cleaning the fitting on the intake that sends the boost signal to the computer and ALDA helped. Adding a shim under the ALDA helped more. From what you describe, I think it needs an ALDA shim... that will boost fuel delivery off idle. ALDA stands for some long German term that you don't need to know. What it does is add fuel as boost pressure rises.

These cars have a reverse Polish wastegate that defaults to open (zero boost) unless the computer sends a vacuum (not pressure!) signal to the wastegate to close it. So if there's any fault in the vacuum system, or the OVP relay is flaky, you'll get no boost at all. Also check timing chain stretch (mine was at 5 degrees, past the limit, so I changed it) and also check IP timing (mine was retarded about 3 degrees when I got the car).

As a guide, the car should get from 0-60mph in about 12-13 seconds, on a flat road, near sea level, timed with a stopwatch. If possible, use a GPS to make sure the speedo is accurate. The car isn't fast, but it's not a slug either. It should be faster than your old 300SD though, and it should get 30-32mpg.