1984 300D No AC, acceleration poor, throttle linkage issues

[bd1308]

Good afternoon! Been a long time forum "lurker" just studying and reading about 300D's. I had one a few years ago and I sold it after I realized it needed lots of work and I didnt have a spot to work on it. Just picked up a rust-free 84 300D, starts right up, glow plugs seem to work okay. No AC, heat works, acceleration is a little poor and there's some throttle linkage issues. Tan on tan, interior is a little dirty but in great condition. Paint seems great too. I'm searching the forums here about how to adjust the throttle linkages but im not finding a lot of information. I love this car so far, and ive only owned it officially for about an hour. It's a good car so far and I believe I only have to do some minor tweaks to get the rest of the car in good shape.

Glad to finally be a part of the mercedes family.

[rrgrassi]

WELCOME!!!

Before you adjust any linkages, first replace the fuel and air filters. Also clean out the banjo bolt that is on the rear of the engine. Carbon build up will prevent any turbo boost signal reaching the alda. Also, do a valve adjustment. If you do not see any or much improvement, then look at the linkages. Poor linkage luberication can cause problems, as can the accelerator linkage bushing mounted on the file wall.

Another thing to check is the tubing, rubber bits and the turbo switchover valve. The valve on my car was bad, and the car was a slug to pick up speed.

I have had my car for 5 years now. It had 216,000 miles when I got it. It's now at 291,000. The A/C was the second major repair I made (Ground up except for hoses. I still meed to replace the vacuum pods and switch valves in the dash). I now need to replace the speedo cable and get the Cruise control working.

If you have more questions, ask away.

[Diesel911]

If you look in the Factory Service Manual under the Control section you will find that most of the linkages have a specific length they are supposed to be.

However, I was in the same situation when I first bought my Car and also had no info.

I figured there were 2 of the linkage rods I could mess with without disturbing the others.

There is a linkage coming up from the Accelerator Pedal to the Bell Crank on the Fire Wall that you can adjust. On mine there was no more adjustment left.

Next there is a Rod coming off of the Bell Crank at the Fire Wall (Also Inspect the Bell Crank to be sure it is still good).

If you trace that Rod Forward you will find a small bolt with a 10mm hex head. If you loosen that Bolt you will find there is a Kidney Slot that allows you to adjust it.

I did not touch all those linkages on the Valve Cover.

The last one is the Linkage that I adjusted is attached to the Throttle Arm on the Fuel Injection Pump.

None of your linkage adjustments should effect the idles speed. There is a Screw and Nut to adjust

[piccolovic]

I agree with rrgrassi. Do all those "maintenance" items first, as that is the first thing to do, along with oil and filter change when you first get any of these cars. After all of the above, and the valve adjustment, if is still has the probs, then, and only then start looking at the linkages, unless you see something obviously bent, or jerryrigged. It's amazing how an basic tuneup will improve things!!!!

[Yak]

The dieselgiant how-to on cleaning the alda line is pretty good. Some info on that site is questionable, some good (not unlike here).

http://www.dieselgiant.com/mercedesaldaboostsystemservi.htm

If nothing else, it shows how nasty the line can be coming out of the intake manifold.

[bd1308]

Add monovalve to the list. I was trying to circulate more air and it was HOT HOT.

Also, what's the nominal operating temp for these cars? There's a bold line next to 80 which I'd assume is the nominal operating temp, but its floating somewhere around 85-90. I guess I can assume i'll eventually need a fan clutch, but I cant test this out now.


Thanks for all the info guys!

[rrgrassi]

My car stay around 90c, even in winter.

A monovalve service kit is not real expensive. The mono valve closes when voltage is present. It is open with out voltage. Check for voltage. Temp wheel in the MIN position on the CCU shoud keep the monovalve closed. If the diaphragm is torn, you can get heat. My car did the opposite, as it failed in cold weather. The torn diaphagm let pressurized water get in and close it, resulting in cold to luke warm heat, after the engine was warmed up.

Testing a fan clutch is easy. It should be stiff to turn the fan, by hand, on a cold engine. On a hot engine, with the engine running, if the fan barely turns or freewheels at engine shutdown, its time to replace the fan clutch.

[Yak]

85-90 is normal.

Monovalve is easy to check - let the car cool, then remove four screws. It should be intact and clean. Scale, torn rubber are the physical signs.

If you've been lurking, then you may be aware the monovalve is switched via ground. Having +12v at the valve only means it has the potential to close. The ACC/CCU/PBU (whatever acronym you choose to use) modulates ground. With full cold on the wheel it should connect the ground pin on the monovalve to ground.

You could check the fuses (remove, clean and replace is prudent anyway to mitigate gremlins) but if the blower is running, then I think the monovalve circuit also would get power.

[tangofox007]

Originally Posted by Yak

The ACC/CCU/PBU (whatever acronym you choose to use) modulates ground.

That's a matter of perspective. The electronic unit for temperature control might see things differently.

[bd1308]

So i changed the pre-filter, I expect to change the spin-on filter as soon as I get a non-leaking purge valve (this one doesnt pump at all -- I opened it and it wasnt doing anything but make a sloshy, pump air into the system kinda action)

Going to autozone today to replace the bulbs, does anybody know if the valve is a autozone item, or do I have to order it via DG, NAPA/WorldPac, etc?

BTW my gf's stepdad gets at-cost stuff from NAPA/WorldPac, so the A/C stuff (which I believe might work but its just out of freon so it wont spin) should be a cheap-ish fix.

Also going to look at the monovalve, and lastly (or maybe first if its easy to fix) figure out why although the ALDA valve seems not to be gunked up my turbo isnt turbo-ing. Its a absolute slouch about 50-55 where my rusty pile I used to own was very quick in that range.

Oh and undo the veggie oil crap the PO used to run in it. The exhaust still smells like the oil I used to put in my RC car to protect the engine between uses, which wasn't diesel.

[toomany MBZ]

I agree about the temp, the t'stat begins to open at 80 C and is fully open at 92 C.

[bd1308]

Excellent. Someone's been doing at least half of the required work, the banjo bolt was almost clean. Lubed up all of the linkages I could find, and copy on the thermostat

I'll check the monovalve

[Yak]

For purge valve do you mean primer pump? This guy?: http://catalog.peachparts.com/ShopByVehicle.epc?q=1984-Mercedes--Benz-300d-Diesel--Injection&yearid=1984%40%401984&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6192%3AED%7C10000135%3AMBC%7C1504%40%40300D&catid=240706%40%40Diesel+Injection&subcatid=240721@@Primer+Pump&mode=PD

If so, I think someone recently posted that those are readily available at truck stops. I couldn't quickly find the thread but I thought it said something like "ask for the black Bosch primer pump".

Oh - and veggie oil? You just opened up a can of worms for troubleshooting advice. Good luck.

[bd1308]

Yep. I was talking about the primer pump.

The veggie oil is gone now, and I think im going to do the maintenance stuff first, then move on to things like the diesel purge and what-not.


Seems to drive well, and is really clean. I'll take pictures if it stops raining.

[charmalu]

Originally Posted by Yak

For purge valve do you mean primer pump? This guy?: http://catalog.peachparts.com/ShopByVehicle.epc?q=1984-Mercedes--Benz-300d-Diesel--Injection&yearid=1984%40%401984&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6192%3AED%7C10000135%3AMBC%7C1504%40%40300D&catid=240706%40%40Diesel+Injection&subcatid=240721@@Primer+Pump&mode=PD

If so, I think someone recently posted that those are readily available at truck stops. I couldn't quickly find the thread but I thought it said something like "ask for the black Bosch primer pump".

Oh - and veggie oil? You just opened up a can of worms for troubleshooting advice. Good luck.

This the thread???
eliminating primer pump


Charlie