300D turbo, new owner questions - PeachParts Mercedes-Benz Forum

E Ray · #1 08-30-2002, 12:17 PM

Great board here guys!

OK, I went out and bought a '91 300D turbo diesel, when I bought it had the typical issues, harsh shifting ........I have done searches and been reading up on this but now the questions start.

What does ALDA stand for??????

Where exactly is the modulator for the trans located?

Does a schematic for the entire vac. system exist some where? I have the manual on CD but can not find much detail on the vac system.....

Tips on checking out the vac pump / system, I have a mitivac, does the vac pump produce a constant level of vac or does it vary with engine rpm?

Thanks

Eric

engatwork · #2 08-30-2002, 01:22 PM

Not sure what ALDA stands for.
The modulator is on the drivers side of the tranny. Climb underneath and follow the vacuum line to the tranny.
I'm sure there is a schematic for it and I would be surprised if it is not in the CD.
The MightyVac is all you need to troubleshoot the system. Not sure about your last question.

E Ray · #3 08-30-2002, 03:01 PM

Jim,

Thanks for the info, I'm sure I will have a million more questions.

Eric

psfred · #4 08-30-2002, 08:33 PM

Vac should be about 12" at idle at the main accessory line -- it is separate from the brake booster line on the 602 engine.

Look for the following: loose, cracked, or mushy rubber connections on the vac lines.

If you have a mitivac, pull one of the lines at the five-way T at the front of the engine (I assume you have the same connections as the 87 300D) and see what you have for vac. If you don't get good vac at idle, check the restriction under the T to make sure it isn't clogged. If it is clear, shut it off and see if all four lines hold vac with the mitivac. I found that my EGR and air recirc transucers were bad and were leaking off all the vac. Plugged the lines (since I don't care if the EGR or air recirc work or not) and my shifting and climate control issues were gone.

Let us know what you find!

Peter

E Ray · #5 09-03-2002, 04:27 PM

Heres what I have found,

Checked the the vac line feeding the series of valve around the air box, EGR, charge control, and pressure control, major leak here, have not isolated that one yet. I assume that Charge control (boost?) must stay connected and work, the other two can be abandoned, right? The other small dia vac lines, one goes up thru the dash this holds vac, the other line goes to the vac transducer holds vac and the vac control valve on the injection pump leaks. Now is the control valve supposed to hold vac, are any of the ports on the injection pump supposed to hold vac? The line to the trans leaks down slowly, not too bad. I also cheked the ALDA unit I will not hold vac, is this normal?

Vac pump output at idle, reading at the tee on the line to brake booster is 23”hg. Reading at accessory? (small) line, connected directly to the pump, all lines removed. 21”hg. Accessory line with every thing connected 5”hg jumping +/- 2.0 not good!!!

Trans still shifts hard but not as bad as before!!!!

Suggestions on what to do next?

Eric

psfred · #6 09-03-2002, 10:05 PM

Eric:

Trace the line from the EGR back to the transducer (round plastic thing, I think). From there, trace the line back to the vac T and pull it, then check to see if the transducer holds vac. I suspect it won't, will just make a fluttering noise. If this is the case, plug the "T" and leave it disconnected. This will cure your vac leak.

You must leave the charge control and pressure control connected (unless the latter is just the air recirc valve -- line from transducer to front of turbo. If so, check as above, both of mine were bad). I don't know if you have electronic boost control, if so, everything must be connected (except EGR).

Transducers cost $60 each.

The ALDA must hold vac, or at least pressure. The boost line from the intake to the ALDA must be clear, and the overboost protection solenoids must be OK (if you have one -- you may not).

You are on the right track -- took me a long time to find the tranducers leaking.

ALDA stands for altitude compensator.

Peter

E Ray · #7 09-04-2002, 03:17 PM

Peter,

The charge control vac transducer is bad, fluttering noise just like you said, now are all three of these the same? So I can swap them about to use the one good one for charge control and plug off all the others? Do you know the part number?

The schematic I have for the engine vac system shows restrictions and dampers in some of the lines, do these play a significant roll in the system?

The ALDA has me concerned, It just will not hold vac. Is this the correct test or is there another way to test this?

Well I’m making headway shifting isn’t so harsh anymore or I’m getting used to it…….

Thanks for all the help so far .

Eric

psfred · #8 09-04-2002, 07:11 PM

Eric:

Yes, you can interchange them, all the same part. Don't know the part number off my head, but check FastLane, should be there. Plug the supply lines for the bad ones (I'd keep the charge control), and I suspect your shifting problems will go away. You should only feel it shift, no noise or snap at light throttle. At heavy throttle, you will feel if thump at bit, but you shouldn't ever hear anything go THUMP.

The ALDA should hold vac and pressure -- check it directly at the connection -- it is the semi-square thing on the IP, below the manifold. If it is indeed leaking, it will have to be replaced. However, the boost system should be open to the manifold (unless you have computerized ALDA control, doubtfull), so checking anywhere else will just suck air from the manifold.

Also, you may have an overboost protection valve on the firewall -- rectangular box with two plastic hoses (one from the manifold and one from the ALDA) with a little cap on top. Check to see that you can blow through the two hoses, and if one is plugged and you blow into the other one, nothing comes out the cap. If it is either plugged or venting out the cap, you won't be getting extra fuel as the boost pressure comes up and the car will be a dog.

The tranny problem and the reason your AC blows up the windshield instead of out the center vents is the two dead transducers.

Peter

E Ray · #9 09-05-2002, 10:38 AM

Peter,

Worked on things a little more last night, the vac transducer to the charge control is bad, as are the other 2, I can pump it down but it won’t hold very long, I will replace this. The vac line to the charge control valve (wastegate) was leaking, replaced that. Now shifting is much better no but still a little abrupt but no chirping the tires from 1st to 2nd , the A/C always worked great, go figure, except for the auto fan, but now that was working this AM for the first time!

Checked the overboost valve, lines are clear, I can blow thru both connections on the valve they both seem to vent out the cap on top, is this right?

Also rechecked the ALDA directly, I can pull a vacuum on it but I leaks down, about 30 sec 15”hg to 0, good? Bad? OK?

Thanks for all the info!!

Eric

E Ray · #10 09-05-2002, 03:20 PM

Ok, now I am searching for the vacuum transducers, FastLane sez its a dealer only part, the local dealer sez its a special order part at $170 each...... anybody know a source other than the dealer? part no?

Eric

psfred · #11 09-05-2002, 06:52 PM

Eric:

No, it should not blow out the top vent unless the solenoid is energized. Try connecting the two lines directly and see how it drives. You may be surprised at the increase in power, may not if the boost control is too iffy.

Try mbz.org for parts, also do a search, there are other sources out there. I'll also check with Hans -- he deals with a place that has better prices. You will need to replace the actuator sooner or later, since it will fail just like the others did.

If you have no boost (from the leaking overboost control), the tranny shifts funny.

Also check the bowden cable for the tranny -- on the throttle linkage beside the ALDA -- it should just be all the way out, very light tension on the spring, with the throttle closed at idle. It runs back into the housing as the throttle is opened, and is probably mis-adjusted like mine was due to the vac leak. You want to get into fourth at about 20-25 mph at light throttle.

Peter

E Ray · #12 09-06-2002, 10:42 AM

Didn’t have much time to mess with thing last night other than pop the hood and look around. The Bowden cable, that’s the throttle cable right? I’ll check into that on Sat. Also there is a cable on the opposite side (exhaust side) of the engine of the inj. Pump, it is connected to the throttle linkage and runs down to the trans., no return spring connected to it does that come into play here? The whole linkage system seems kinda sloppy too, is that right?

Thanks

Eric

psfred · #13 09-06-2002, 07:26 PM

Eric:

The bowden cable in question is the one that goes to the tranny. Should have a long white screw adapter at the IP bracket to adjust the length of the free end.

There should be a spring on the end -- wide coil type. The cable should be all the way out of the housing, with no free play and very slight tension on the spring at closed throttle position, and retract all the way into the housing at wide open throttle. If it doesn't move, you have either a broken cable or a missing bit -- I'll check mine later to make sure I've given a good description.

This cable controls shift timing (along with the vac, which also control harshness). Late shifts are always harder than early ones.

Peter

E Ray · #14 09-07-2002, 09:10 PM

Things are coming together here, messed with thing a little mre today, new door checks, replaced the fuel filter, screen and all fuel hoses.

The bowden cable? there is one cable on the throttle linkage with the white adjuster thing, except it goes to thru the firewall, throttle cable? anyway I gave it a few turns to slacken it a bit more and now the trans shifts more where it should, go figure.

Still searching for a Vac transducer for the charge control circuit, pulled the 2 that control the egr and pressure control, both bad, so no luck there. This brings up the question what is the significants of the pressure control, the manual shows a flap in the compressor outlet line? dosen't charge control regulate the turbo output?

Eric

psfred · #15 09-07-2002, 09:47 PM

Eric:

I will have to check Monday -- I only have two transducers, one for the EGR and one for the air recirc valve that vents the turbo off throttle (and causes cruise control surges, too!). I think the 91 may have electronic control of boost, too, in which case you need to have it working. The other two disconnected won't kill you. If you have electronic boost control, the tranducer will operate the waste gate on the turbo -- a valve in the exhaust side to control the pressure in the clean air side.

Peter