1985 300 D slow on take off.. - PeachParts Mercedes-Benz Forum

Salty Dog · #1 03-09-2011, 01:58 PM

Hello Gents...I was hoping I could get some input on an apparent issue with my 300D. Not sure if its the nature of the beast or not since it is my first Mercedes. I have owned it a year now and went through the basics at 175K after buying it off an older gentleman who never abused it. I had the valve lash adjusted and replaced the transmission filter, replaced the shifter bushings and she runs great. Starts perfectly, doesn't smoke much and once she warms up seems to have better take off power. I just feel possibly something might improve the take off from a dead stop, power wise. I just put a little trailer hitch on it the other day and although I don't intend on hauling anything more than a jet ski...sometimes wonder if it would make it up a steep hill...any suggestions or leave it alone? Thanks

toomany MBZ · #2 03-09-2011, 02:42 PM

This would be more appropriate in the Diesel Discussion section, but I'll try to help.

Some of these cars started in second gear, is yours?

Inspect the rubber bushing on the firewall, have someone press on the go pedal while you observe. You're looking for cracks, mostly, that won't allow full pedal travel.

Also inspect the "ALDA". There is a pressure line on the manifold back near the firewall behind the air cleaner, follow that line to a device on the left side of the firewall (busy place!) then it travels to another device on the Injection Pump. Make sure this line is clear of obstruction, usually, there will be a build up of oil and soot near the manifold, clogging said line. This to open to allow turbo pressure to reach the "ALDA".

Salty Dog · #3 03-09-2011, 05:16 PM

Thanks for the input. Haven't found the technical forum thread yet but will figure it out sooner or later...I have manually downshifted the vehicle and it is definately starting out in 1st gear. I looked behind the air cleaner and off the top of the exhaust manifold I found a little electrical contact switch which I popped off and replaced. I noticed a line on the back of the manifold which goes to a vacuum switch behind the brake booster. Is that possibly the ALDA switch? I remember I had to replace that last year also because of starting & vacuum issues.. but kind of afraid to pop that off without removing the switch from the firewall again..Thanks again. Bruce

toomany MBZ · #4 03-09-2011, 05:53 PM

Quote:

Originally Posted by Salty Dog

I noticed a line on the back of the manifold which goes to a vacuum switch behind the brake booster. Is that possibly the ALDA switch? I remember I had to replace that last year also because of starting & vacuum issues.. but kind of afraid to pop that off without removing the switch from the firewall again..Thanks again. Bruce

That line goes to a switchover valve, which sends another line just like it to the ALDA, a round silver item, circled in red.

That has nothing to do with vacuum, just the opposite, pressure.

Nothing to do with starting either.

winmutt · #5 03-09-2011, 06:03 PM

Plug the ARV and EGR lines. Verify that the max stop is being hit on back of IP with pedal fully depressed. Adjust valves. Pop test injectors. Then think about adjusting the ALDA, cleaning it is always a good thing.

thatguy · #6 03-09-2011, 06:09 PM

Try changing the fuel filters and running a Diesel Purge as well. Another thing to consider is bypass the trap-ox if you have one on your car, they tend to plug and are just giant heaps in general.

dieseldan44 · #7 03-09-2011, 06:15 PM

I got my '85 for a song because it had 'no power on takeoff'.

The boost line going from the overboost valve to the back of the turbo was broken at the banjo bolt. A quick cleaning and reconnection restored all power.

Paulc66t · #8 03-09-2011, 06:58 PM

I would check the boost limit line as described by DD44. If it is clean and functioning search for "alda adjustment". Also wouldn't hurt to check injection timing. I had to take care of all these things before my 83 was able to get out of its own way.

frankengrant · #9 03-09-2011, 08:19 PM

Quote:

Originally Posted by winmutt

Plug the ARV and EGR lines. Verify that the max stop is being hit on back of IP with pedal fully depressed. Adjust valves. Pop test injectors. Then think about adjusting the ALDA, cleaning it is always a good thing.

Here is the ARV line:

Did I plug the right vacuum line for the ARV? (Pics, 1985 300D, CA)

Salty Dog · #10 03-09-2011, 11:45 PM

Thanks Gents...will check these things out in the morning. Thanks for locating the parts for me. First I will check the line to the ALDA valve as first suggested then I will try plugging the EGR and ARV valves. The valve lash was already done and I believe the last mechanic also checked my injection timing because the engine was idling bad and shaking the car...Any suggestions on the adjusting procedure for the ALDA valve?

vstech · #11 03-10-2011, 08:37 AM

First off, welcome to the forum!
now, before tackling adjustment of the ALDA, I'd have someone step on your accelerator pedal and I'd watch the linkage travel. the Injection pump lever has a stop on it you want the be SURE the linkage is allowing full travel to the stop with the pedal floored.
next I'd put a new pair of fuel filters and a new air filter on there. then I'd pull the line connections off the alda and off the OPV and the line on the intake manifold. make sure they are all clean and clear.
lastly I'd attempt adjustment of the ALDA...

Salty Dog · #12 03-10-2011, 09:49 AM

Please excuse my ignorance...Plug the ARV and EGR lines. (do I take the car for a drive after I plug these lines?) Verify that the max stop is being hit on back of IP (What is the IP? )with pedal fully depressed. Adjust valves. Pop test injectors. Then think about adjusting the ALDA, cleaning it is always a good thing

kerry · #13 03-10-2011, 09:58 AM

Don't do any of those things before swapping out fuel filters and checking the overboost/alda line from the intake manifold.

Salty Dog · #14 03-10-2011, 11:43 AM

What is a diesel purge? I did run a bottle of injector cleaner through it last week and did notice a little improvement in top end performance. I have a clear fuel filter and don't see it starving for fuel when I run it at a fast idle. How do you pop test the injectors ? Does that require removal? I unplugged the top line from the switch over valve and blew back to the ALDA but no air would go through. The line from the bottom of the switch over valve looks intact to the back of the manifold.