Tuning the WRD

[RonDwyer]

I fixed the leaky CSV last weekend, and the WRD just barely lets a tiny bit of air past it which leads me to believe it needs an adjustment. 

Question, as the thermostat warms up, does the plunger extend into the pump or retract upwards?

Does adding the .010 shims help tune this assembly to be able to close off the air valve completely?

If I get my air valve completely closed by adjusting it, then the final step I hear is a fine tune adjustment to the mixture screw?

The tech manual was not too clear on the last steps.   

Does anyone have a source on these shims? 

[Benz Dr.]

That depends on which engine you have. If you have a 280SL, you will need to add a shim or two on the top of the sliding valve that's inside of the housing so it will move a bit lower when fully warmed. This should shut all of the air off and also move the rack inside the IP to the fully warmed position. You may need to make adjustments at the barometric compensator and the idle mixture knob depending on how rich or lean you are at hot idle. This requires driving your car to get the system fully warmed in most cases.

[ja17]

Shims are used in two places on these WRDs. The round shims in the plunger (under the top stage) of the WRD, will change two things; the fuel mixture during warm-up and the timing and travel of air valve piston. The oval shims under the bottom stage, will change only the fuel mixture during warm-up.
Changing of the small round shims on the slide valve, will change the position of the air valve piston, but it will also change the fuel mixture during warm-up. If you do this you may have to adjust the warm-up mixture with the oval shims on the bottom stage of the WRD also. Make sure your air passage is closed off at the correct temperature first. Adjust warm-up fuel mixture from there. A lot of owners notice a slight air leakage even when the air piston is in the closed position. You should make sure your heat feeler functions correctly before adjusting the air slide piston with shims. Your engine thermostat must also allow the engine coolant to reach correct operating temperature.

[stickandrudderman]

Personally, as long as the mixture is not being enrichened I am happy to live with a small air bleed from the WRD. It is, after all, doing exactly the same as the idle screw so a 1/4 turn on the idle screw to compensate is all that's needed.
You need to know how to ensure that the device is working correctly in all other respects though.

[wwheeler]

My WRD always leaks a tiny bit of air when warm. I have added the round shims to make sure it was completely shut off. At some point, adding more round shims did nothing for the very slight air leak when warm. That is the point in which you know it is shut off.

I attribute the slight air leak to wear on either the cylinder bore or piston. Both of which are aluminum. It has no real seal and relies on the clearance fit of the piston to the cylinder bore and also an oil film. So if you have damage on either part, you will get more air leakage. This all of course assumes everything is working properly. 

Joe makes a good point about the thermostat. Being in Texas, I have always been concerned with overheating. I had the cooling system rebuilt and I added a cooler thermostat. I then discovered that the engine took forever to completely warm up. The WRD was operating in a slightly opened mode for longer than I wished and caused idle quality issues. I changed the thermostat one step hotter and all the problems went away. 

[RonDwyer]

I think what had not previously been totally clear was that there are shims above the valve.  In the diagram on the WRD page it omits descriptions that many of us would find useful. 

Adding some descriptions to the missing numbered parts would be helpful.  I am going to take a close look at the upper shimming tomorrow. 

[wwheeler]

#10 are the oval shims. #7 is the piston. #6 is I think is a steel washer that must remain and #5 are the round shims that can be altered. It is not totally clear what the difference is between #5 and #6.

Maybe that helps.

[Benz Dr.]

5 could be the small wire clip that holds the shims in place.

[wwheeler]

Possibly. But I think I see a groove in the ID of the piston much higher up. I also seem to recall that the wire clip is up high and doesn't compress the shims. Either way, it is obvious when you get it apart.

[Benz Dr.]

The wire clip is just above the shims. I guess they left enough room to fit a couple if you need them but there isn't all that much distance between the last shim and the wire clip.

[Andrew C]

Without a very reliable CO tester you will find setting up anything on the injection pump very difficult and extremely time consuming. I worked on these cars as a Mercedes trained mechanic in the early 80's.  We didn't play around with all the settings without a CO tester.  Every adjustment affects the pump. it's all connected. I've been reading the posts on the CSV. WRD. Plugs. Points. Timeing.  And I might be wrong but I haven't seen one mention of the CO values for warm up. Full throttle. Cruise and idle.  That's why I think there's so much information about the MFI.

[wwheeler]

Most are not fortunate enough to have a CO meter and just have to make do. I agree, to optimize performance that is a necessary tool. There are several posts here with people who have rigged up a CO meter and had success.

But in this case, the warm up mixture is not critical since it is only for a short time (that is IF everything is operating the way it should:. As long as it starts ok and runs decently for that brief time.

I personally don't mess with the full range or partial range screws on the pump. To me, that is where you can get into serious trouble. But adjusting the WRD, idle mixture and using the B. Compensator as the full range, is straight forward and completely reversible if you know how they function. Same theory applies here as to all of car restoration, know your limits and don't get over your head.   

[Benz Dr.]

Possibly. But I think I see a groove in the ID of the piston much higher up. I also seem to recall that the wire clip is up high and doesn't compress the shims. Either way, it is obvious when you get it apart.

Just to clarify, the wire clip is on the inside bore of the piston and above the round shims.

[Andrew C]

You can use the split linkage test during warm up.  But you have to be quick.

[RonDwyer]

One thing not mentioned here is the likely poor condition of the injectors on an old car.  I think before adjusting the pump I am going to try to locate one of Mercedes source' injector tools.  Anyone in the SF Bay area want to go in on one or rent it?  Chances are I'll never need it again.  A bad spray pattern is going to contribute to the rich problem too.  My eyes water when I stand behind this car. 

[wwheeler]

You can also send out the injectors to anyone who rebuilds pumps and they can clean and test. Then you will know for sure. There are a couple in CA that I can think of.

[Benz Dr.]

One thing not mentioned here is the likely poor condition of the injectors on an old car.  I think before adjusting the pump I am going to try to locate one of Mercedes source' injector tools.  Anyone in the SF Bay area want to go in on one or rent it?  Chances are I'll never need it again.  A bad spray pattern is going to contribute to the rich problem too.  My eyes water when I stand behind this car.

That kind of rich sounds like a pump problem. You could always try turning the barometric compensator by removing a couple of small shims first. I've fixed quite a few rich runners that way.

[RonDwyer]

The Mercedes Source injector tester works to 3,000 Psi for diesels.  With the appropriate solvent, this tool will certainly help clean and resurrect faulty gas nozzles.  I was thinking Kroil would be an ideal solvent of last resort as it has a small % of acid to it.  Note: anyone using Kroil should avoid breathing it or getting it on bare skin.  It truly is the only penetrating oil in existence, it works.  My millwrights use it in foundries, paper mills, etc. 

[Tyler S]

Keep in mind no amount of cleaning will fix an injector that has corrosion, pitting, wear, or damage to the pintle or seat. Cleaning them is usually a crap shoot but you may get lucky.
You may get 3 or 4 to function properly so you are left thinking "I only need 2 new ones". Mixing/mismatching old and new injectors can open up other issues. Uneven idle, inconsistant lean or rich burn across cyls, etc.
If in doubt, send them out.
Or buy all 6 if you find any with issues.

[RonDwyer]

Sending them out is false economy if I can buy the tool and do it myself.  It costs the same and I see what the results are. 

If I have 4 or 5 that cleaned up and are now operating properly, and need one or 2 new ones, and they all spray the same at the same pressure, I claim success. 

Next time I have a set to check, i think i'll leave them in the car, fill them with kroil, put the injector lines back on and let it sit overnight.  Then start the car to see what happens.  Let the fuel pump do the pressurizing. 

[wwheeler]

Whether you buy the tester or not depends on you. If you LOVE to fiddle around and time is not an issue, then by all means get the pump. I have another brand and I can tell you it is not automatic cleaning. You try this, you that and finally it starts working. Sometimes it never works no matter what you try. For the folks who have little time and just want to plug and play, the tester is not a good option. IMHO.