Please help with problems on my 85 300D - PeachParts Mercedes-Benz Forum

Chetcpo · #1 07-27-2008, 02:32 PM

Hello everyone. I'm new here, this is post #1. I just bought a 1985 300D with 160k miles on it. The owner drove it daily and it seems reliable, but it does have some issues I'm looking for advice on. I only paid $740 for it so I was expecting some things would need to be fixed.

1. The A/C and tach don't work. I did a search and from what I read I see the problems are somehow related, but no specifics on why. I also saw a thread in which a gentleman had a corroded EGR computer plug that caused his tach to fail. I'll give that a look, but I was also wondering what else I should check.

2. It seems painfully slow. I wonder if the turbo is still making boost. After driving it my brother in law challenged me to a 60 foot race. Him on foot and me in the 300D. I politely declined.

3. Rust. It has some rust in the corners of the lower fenders and along the bottom of the rear window. Also some on that piece that extends from the front fender under the bumper. This is something I have fixed on other cars, but I was wondering what other "trouble areas" in less obvious locations I should inspect.

Thanks in advance,
Chet

johninva · #2 07-27-2008, 03:02 PM

most likley egr computer connection or egr computer itself, if you saw the other thread you know where it is and what it looks like. A/C probably still wont work after that unless your lucky. If someone could win a race on foot something is wrong. check out dieselgiant.com for maintenance tips. there is a vac line that goes to the back of the intake manifold that gets clogged up with soot that could be affecting your performance. diesel giant outlines the procedure. rust - spare tire well, bottoms of doors, jack points ...

Jeremy5848 · #3 07-27-2008, 03:13 PM

Chet, welcome to the forum and congratulations on your purchase. None of your problems are particularly serious except perhaps the rust (depends on how bad it is).

The a/c and tach issue may indeed be related. The 1985 300D Turbo (W123, OM617) had some unique electronics. The tach signal is picked up by a sensor near the flywheel of the engine. It can go bad; its wires can be damaged. The signal next goes to the EGR computer. It is located behind a panel on the right side of the right front seat footwell area. I have not heard a lot about it failing but other than the tach, all it does is control the EGR function and most of us would be happy if it died anyway.

In the later W124 cars it also controls idle speed but not in your car.

From the EGR computer, the signal goes to the instrument cluster where it drives the tachometer. The tach is simply a meter movement; it could just as well say "volts" as "RPM." You can remove the instrument cluster from the dash and carefull test the tach with an ohmmeter. The tach meter itself does not often fail, from what I read here.

This same tach signal also goes to the "Klima" relay, a (literally) black box that lives in the engine compartment near the brake booster. Klima looks at the tach signal and several others and decides whether the a/c compressor should be allowed to work. Klima is a known failure point and without it the a/c won't work.

You can test the compressor by removing the wire leads at the clutch and temporarily connecting them to a 12 volt battery; with the engine not running, you should get a strong "click" as the clutch engages. If you do not get a click, the clutch may be bad. If the clutch engages with everything connected and the engine running, you may simply be low on Freon but the non-working tach tells me it may be more than that.

You need to do some snooping under the hood and tell us what you find, then we can help you more. Apparently you have already used the search function; everything you report as your problems have been solved before you you will be able to shamelessly copy what others have done (why reinvent the wheel?).

I'll let someone else address the rust problem.

Jeremy

junqueyardjim · #4 07-27-2008, 03:21 PM

Typical zero to 60 time is about 16 seconds. That is when they are running like new. Like the previous writer said, search a little and you will find a lot. Diesel Giant is noted for excellent pictures and write ups. Rust in rear suspension parts and behind and under the battery box are bad, as are rust areas in the floor. Pull the battery and take a good look. Pull the floor mats and see what you can find. That rust under the front bumper is actually the extreme ends of the front fenders and they come together in the front center. My theory is when that is all rusted up, it is best to to cut it off. Doesn't conform to Benz fit and finish, but it works. The way they were built and the body undercoat used did make these good old cars quite prone to rust. Once it gets a good start, like cancer, it's usually terminal, though many people get a number of good years service on them, even with the rust.

JimmyL · #5 07-27-2008, 03:37 PM

I imagine I was the one referred to with the corroded EGR computer connector. It was a mess!
Here is a link with a pic of how to bypass your Klima relay so that your AC will work without tach function. You can use it that way until you find the tach issue.

http://www.peachparts.com/shopforum/showpost.php?p=1344855&postcount=3

Chetcpo · #6 07-27-2008, 04:00 PM

Thanks guys. Lots of good information there. I will investigate the things you mention further. I really appreciate all the help.

tobybul · #7 07-27-2008, 08:13 PM

Quote:

Originally Posted by johninva

most likley egr computer connection or egr computer itself, if you saw the other thread you know where it is and what it looks like. A/C probably still wont work after that unless your lucky. If someone could win a race on foot something is wrong. check out dieselgiant.com for maintenance tips. there is a vac line that goes to the back of the intake manifold that gets clogged up with soot that could be affecting your performance. diesel giant outlines the procedure. rust - spare tire well, bottoms of doors, jack points ...

Don't just clean the banjo bolt and the boost line. If you follow this line it leads to an overboost valve located just behind the brake booster. This can get clogged up. Take it out and spray it with brake cleaner. It could have lots of soot and gunk. Reinstall and see if it gets peppy. Whatever you do, do not mess with the ALDA!!!

Chetcpo · #8 07-27-2008, 08:34 PM

Roger that, I promise not to mess with it...

But first, what is the ALDA?

Diesel911 · #9 07-27-2008, 09:30 PM

Restricted fuel and air filters also can cause low performance as well as the valves not having been adjusted for a long time (as the valves/seats wear the clerances get tighter and need to be re-adjusted).

vstech · #10 07-27-2008, 09:37 PM

the alda is the square box ontop of your IP with a clear line attached to it. it has a black plug on top of it, under the plug is a screw that will adjust the amount of fuel it sends based on boost to the car... the O.E. setting is just fine! once boost signal is restored to it, you will feel PLENTY of boost! the 85 is a strong turbo!
oh, and typical 0 - 60 MPH time for an 85 is from 11 - 13 seconds...

and with this many rust spots, I would look under the battery tray. rust there can get your footwells quite wet.
clean out the sunroof drains, and clean out the hood hinge pockets of debris, and flush out the drains back there too.

ImBroke · #11 07-28-2008, 07:58 AM

And, put in your location. Some of us on here are willing to come to you to show you things and help out.

bgkast · #12 07-28-2008, 11:12 AM

I had these same problems when I got my (now sold) '85.

As has been mentioned the lack of power is most likely due to the ALDA not receiving a boost signal from the turbo. You have a clear (or what used to be clear) plastic line running from a bolt at the back of the intake manifold across the fire wall, through an electronic valve, and then to the ALDA on the injection pump, and in the '85 to the "blue flying saucer" which helps control how the transmission shifts. The ALDA limits the amount of fuel to the engine until boost pressure is built to prevent black smoke. Clean out this hose and the valve. In my car's case the hose had come unplugged and was just venting to the atmosphere.

The EGR computer can cause tach problems, but I think the most common issue is the overload protection relay. It is located on the right side of the car behind the glove box. It has a fuse in it that can burn out, but in my case the whole thing was bad. I plugged in a new one and my tach then worked. In this car the AC will not come on if the engine is under a certain RPM, so if the tach is not working the AC will never come on. As has been stated above don't be Surprised if the AC still does not work after you fix the tach.

As for the rust, the common areas I have seen are the hood hinge pockets, under the battery tray, under the sound deadening material in the rear seat foot well and the sides of the trunk, particularly just behind the rear wheels. Post some pictures of your rust for more feedback.

Good luck!

tobybul · #13 07-29-2008, 12:00 PM

Quote:

Originally Posted by vstech

the alda is the square box ontop of your IP with a clear line attached to it. it has a black plug on top of it, under the plug is a screw that will adjust the amount of fuel it sends based on boost to the car... the O.E. setting is just fine! once boost signal is restored to it, you will feel PLENTY of boost! the 85 is a strong turbo!
oh, and typical 0 - 60 MPH time for an 85 is from 11 - 13 seconds...

Ditto on the ALDA. I know some members advocate opening up and adjusting the ALDA. After doing that however, I regreted it. For one, that was not the cause of the sluggishness of my car. It was simply a dirty boost line. The ALDA is now back to factory setting. There is a reason why the MB sealed the ALDA. They did not intend for it to be messed with.

Chetcpo · #14 07-30-2008, 09:35 PM

I took some pics of the rust for you to see what I'm talking about. I uploaded them to some webspace I keep. Sorry for the dark pics. Here are the links:

Here is the worst problem. Note the open hole in the front of the fender well.
http://www.locostusa.com/pics/mercedes300D/rrfenderwellrust.jpg

Look what having that open hole did to the inside. Here's an interior view of the RRpassenger seat door sill.
http://www.locostusa.com/pics/mercedes300D/doorsillrust.jpg

This looks like an easy fix:
http://www.locostusa.com/pics/mercedes300D/behindlrfender.jpg

I'm not sure about this:

http://www.locostusa.com/pics/mercedes300D/rustunderfrontbumper.jpg

View of front of car:

http://www.locostusa.com/pics/mercedes300D/front.jpg

View of rear of car:

http://www.locostusa.com/pics/mercedes300D/rear.jpg

On a positive note it ran a bit better today. Turns out you really need to push down hard on the gas pedal. Harder than what I'm used to, but if you really stand on it, it will take off pretty good.

I'm debating whether or not to try and fix this thing or just sell it and get my money back. I fear the rust is going to take a lot longer to fix than I had counted on.

Oh, and I added my profile location per request.

ImBroke · #15 07-31-2008, 08:20 AM

What I don't like about the door sill rust is that the seat belt bolts there. Doesn't look too structurally sound anymore. This is why I had to make my 82 a parts mobile. I found floor pans, but from Germany and I wasn't sure what shipping would be nor if they would even make it here without getting all bent up. The other rust looks minor.
Yes, these cars do drive differently than gassers.