Author Topic: W108 250SE injection pump- teach me  (Read 337 times)

K-Jet

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W108 250SE injection pump- teach me
« on: December 29, 2021, 19:59:00 »
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.
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K-Jet

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Re: 250SE injection pump- teach me
« Reply #1 on: December 29, 2021, 20:00:51 »
The remaining pictures. Sorry for the clumsiness- I wish I knew how to put the pictures in line with the descriptive text!

ja17

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Re: W108 250SE injection pump- teach me
« Reply #2 on: December 30, 2021, 04:33:06 »
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.
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2006 Mercedes Sprinter Van
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1982 300TD Wagon turbo 4spd.
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback

ja17

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Re: W108 250SE injection pump- teach me
« Reply #3 on: December 30, 2021, 04:34:02 »
Your pictures are very good. Just ask questions and we will teach you!
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2006 Mercedes Sprinter Van
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1982 300TD Wagon turbo 4spd.
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback

K-Jet

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Re: W108 250SE injection pump- teach me
« Reply #4 on: December 30, 2021, 21:36:51 »
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

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Re: W108 250SE injection pump- teach me
« Reply #5 on: December 31, 2021, 07:21:10 »
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 !
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2006 Mercedes Sprinter Van
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1982 300TD Wagon turbo 4spd.
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback

K-Jet

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Re: W108 250SE injection pump- teach me
« Reply #6 on: January 13, 2022, 20:18:37 »
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

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Re: W108 250SE injection pump- teach me
« Reply #7 on: January 14, 2022, 00:01:22 »
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.
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2006 Mercedes Sprinter Van
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1982 300TD Wagon turbo 4spd.
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback