W108 250SE injection pump- teach me

[K-Jet]

1971 280SE with a 250SE motor in it.

I have no history of the pump other than it has been installed in this non-running car for about ten years. With much patience, the car will start, and will run OK (but prouce little to no power) until warmed up. Then it dies. I've been through all the adjustment and tuning. The MFI pump is what's left to investigate.

I have the pump out and have opened it up. I don't know enough to know what I am seeing, but what I'm seeing seems strange to me. I'm ignorant, so that strangeness doesn't mean much.

On to the pictures:

The space cam and stylus, with throttle closed. Note the meaty part of the space cam off to the right of the stylus.

When the throttle is opened, the space cam turns clockwise, and the meaty part of the space cam moves away from the stylus. The stylus moves across an essentially flat part of the space cam, and the rack moves only a faint twitch. Is that right?


As I understand it, the rack should turn the black collars at the top of each cylinder to change the amount of fuel that goes to the injector. From full throttle to no throttle, the collars don't turn more than about two hairs breadths. Note also that cylinder number 2 gets no fuel- it seems like the spring does not push the cylinder back down. I can move it with my fingers, but it doesn't move on its own.


The regulator end, with adjustment screws. Moving the centrifugal weights does exert spring pressure on the front of the space cam. but does not move the rack or the space cam.


Little known fact:Bosch makes black boxes in silver. Atmospheric pressure can on the right, (removed) temperature sensor on the left. These bars and linkages and springs and ladders do something. I think.


I think I read that you are supposed to be able to move the rack by threading a 4mm bolt into the end of the rack and moving it. This one is locked up tight.


This is clearly beyond me, and will likely be going off to the MFI pump day care as soon as I can locate a trustworthy one that doesn't require arms and legs in payment. I'm open to advice and suggestions and help.

Teach me. Please.
__________________

[K-Jet]

The remaining pictures. Sorry for the clumsiness- I wish I knew how to put the pictures in line with the descriptive text!

[ja17]

The piston in #2 is stuck in it's cylinder. Take the 19mm fitting off the pump over #2 and remove the spring and check valve. You will be able to see the top of the small piston in it's cylinder. Soak the piston in penetrant and or alcohol. Use a soft metal rod or hardwood to tap downward on the top of the piston. Rotate the engine slightly and tap downward. Re-peat as needed. Eventually the piston should return on its own at which point you will see the rack move freely also. Do not allow the cylinder to rise in the bore and rotate during the process or it may loose its orientation and calibration.  Assemble after everything is working. Be sure to torque the 19mm fitting to 19-21 ft.lbs. If it is too loose pressure will not build. If it is too tight you can crack the pump housing.

[ja17]

Your pictures are very good. Just ask questions and we will teach you!

[K-Jet]

WD40, brake cleaner, and a toothbrush have loosened everything up. The rack moves smoothly, the number 2 injection cylinder is unstuck. Life seems really really good right now!

No adjustments made, so hopefully nothing to regret.

Maybe reassembly, reinstallation, and a test drive tomorrow. We'll see.

Thanks for giving me the confidence to try this.

[ja17]

Align the marks on the IP. Set the engine at 20 degrees after TDC (Compression stroke #1 cyl. and slide it in place. Don't forget the splined coupling between the engine and the IP !

[K-Jet]

Status update: Marks aligned, engine to 20ATDC, pump installed, everything else installed, plug wires corrected and it runs so much better.

BUT, no luck in bringing the idle up beyond about 500 rpm. Timing is set. The idle air screw only made a difference in the closing direction. On the pump, we tried all the way out to 10 clicks in each direction with no apparent effect. Cracking the butterfly fixes the problem, but I don't think that's how it's supposed to be done.

What next?

[ja17]

Make sure all your linkages are correct. Is your low idle with a cold engine, warm engine or both? Also, do you know how to do the split linkage test? Make sure your ignition timing is correct also.

[Francis Abate]

If you still need help, I can direct you to a place in KS that is highly skilled in these pumps and will not cost you an arm and a leg.  The group works mainly on Diesel trucks and tractors but one older guy there is experienced in the gasoline and German car specific pumps as well.  I had my 250SE W111 pump cleaned, repaired and calibrated for about $400.  Feel free to contact me by phone or email if you like.

[K-Jet]

Francis,

Thank you! I'll be in touch if I need the contact information. At this point the pump has been cleaned but it could still decide to cause trouble.

Thanks for yo ur generosity. Congratulations on your career change, too!

Dru

[Benz Dr.]

...
This is clearly beyond me, and will likely be going off to the MFI pump day care as soon as I can locate a trustworthy one that doesn't require arms and legs in payment. I'm open to advice and suggestions and help.

Teach me. Please.

A bit off topic but kind of interesting:

The saying " It cost an arm and a leg "  has historical significance. Before photography was introduced, the only way to have your portrait done was by painting. The price depended on how much the artist had to do. Your face was a basic price, your arm or hands were an additional price, and your included legs were the most costly. Hence you paid an arm and a leg.

Now you know the rest of the story.

[djbain1210]

This forum and particularly, this thread has helped me tremendously in troubleshooting the MFI pump on my 1967 250SE, however, I now have a dilemma that I've yet to resolve.

When it became necessary to work on my injection pump to free some stuck pistons, I wound up with a spring for which I cannot find the attachment location (I know, that doesn't sound good). It is not a spring I removed so it apparently dislodged while turning the pump upside down and all around during cleaning. It showed up near the centrifugal weights. I have attached a photo of the spring hoping someone will recognize it and be able to point me in the direction of it's intended purpose and attachment location. Any help will be greatly appreciated!

Please advise whether it would be more appropriate starting a new thread since this one is somewhat older.

Thanks!

[K-Jet]

Yeah, I don't know, and my pump is closed up and reinstalled. I would guess it connects to two things in the control section of the pump - not very helpful I know. I'd suggest cleaning the pump as best you can and seeing how smoothly things move and if there's a place where needed motion is lacking. Look there.

[djbain1210]

Thanks, I'll keep looking. Everything seems to be working fine but I'm reluctant to button everything up and reinstall the pump. Although, I guess it wouldn't be too much trouble if it at least allows me to get the car running. Maybe whatever symptoms show up will give me an indication of where the spring is needed. Thanks again. Sorry for the late response, we moved during the last couple of weeks and I just got my computer unpacked.

[BartSt]

Hey,
This is a 230sl pumpI'm trying to fix.
The picture shows a similar spring which need to be attached to the knop in the background.
Hope this helps.
Bart