MFI Rack Movement

[MY911S]

Hi All,

Been trying to figure out how movement at the throttle hinge mechanically translates to movement at the rack. See 2 red arrows. I've been watching videos and pics of what I can get a hold of but can't seem to figure out the mechanical linkage that allows for this movement. When I move my hinge nothing else moves...and nothing seems to be mechanically connected from that hinge to the rack. Thanks in advance for any insight.




At 9:23 in this video you can see the movement I'm referring to.
https://www.youtube.com/watch?v=LTs2qhfXNtU&t=200s

[Tyson Schmidt]

I can see your main rack moving when you move the throttle lever.

Pull the rubber cap off the back of the pump. That is the back side of the main rack. It doesn't move that much, but you will feel it move when you move the throttle lever.

The way it works is the space cam rotates with throttle, and plunges fore/aft with rpm. The stylus rides on the space cam, and as it moves topographically on the 3D space cam, that causes movement of the main rack.

[MY911S]

Hi Tyson, thanks for taking time to respond! That video isn't of my pump. I just linked it to illustrate what I was referring to. When I pull the throttle lever as shown in the video my rack does not move at all. It is frozen for sure because it won't budge with pushing against it on the other side (where you remove the cap as you pointed out).

But I think your response contains the answer to what was puzzling me : "space cam rotates with throttle, and plunges fore/aft with rpm. The stylus rides on the space cam, and as it moves topographically on the 3D space cam, that causes movement of the main rack" - and so the linkage that I was trying to figure out is that moving the throttle lever causes movement of the stylus which moves the rack.

And I think the answer to my question is the mechanical linkage between the stylus and the main rack...is what causes the rack to move...maybe. I'll take a look again...Here's a video of my actual pump -019 .. the rack doesn't move...i dont see the stylus moving as well

https://photos.google.com/direct/AF1QipNmXPRGbKt1JUVBubkpAOK9Zfb6M6iMFf3V1A1mNSJj2f PGrl8T7uZUozM3iGcISw/photo/AF1QipM-9pwACwYttDfRJQsZe62AlKKJxtXiBi7WpVjF

[Jonny042]

The stylus moves a very small amount - if your rack is frozen it's possible something else in the system is moving, like the baro cell, the thermostat, etc.

[MY911S]

I see thanks Jonny. Doesn't even look like the stylus is touching the space cam. I'll take a closer look at the entire system again. Thank you.

[Jonny042]

If the inner working of the pump are "gummed up" that's certainly possible and would explain the lack of movement.

[356RS]

One or more of the plungers are frozen in they're cylinders. Main rack will not move, stylus will not move. Everything else will look ok.

[MY911S]

Thanks guys. Yep the plungers are frozen for sure the springs don’t move. Now I have to figure out to unfreeze them

[Jonny042]

The answer is one post above yours...... send it to Mark!!

[MY911S]

I'll probably need to send it for calibration anyway.

[r lane]

WD 40 is your friend, amazing the things it can fix. If it is all gummed together, you might get lucky, corrosion, rust probably not. They are very robust units, but their tolerances are critical and don't like things other than fuel. I possess general knowledge, Mark significantly more. Bob

[MY911S]

When the plungers do move up and down does the big red circle. move or the medium circle or the small (looking into one of the inline ports with the check valves removed). I was reading in the mercedes forum of someone pushing down the plunger with a golf tee which makes me think the small circle.

https://photos.app.goo.gl/CXDJszRGQphQzCGs9

[Jonny042]

Yes, the small circle. If you are going to push down on it you will want to make sure the cam that actuates the plungers is out of the way and not holding it up.

If the rack is stuck and the plungers seized (you can tell by that picture they are all stuck in the fully raised position) you would be wise to soak it in some penetrant before going any further.

I would suspect that unless you are planning to do all the work on the pump you;d be wise at this point to seek professional help.

Not to say it can't be done by a resourceful individual with plenty of time, tools, and knowledge, but it's a long road......

[MY911S]

Thanks Jonny appreciate the confirmation! Yes I've been doing the soak, poke, rotate the sprocket cycle. It is taking some time

[47silver]

Send it to 356rs and install it. Save you time and money

[MY911S]

I actually thought about doing it very similarly as this:
Technical Tips - The Home of the DIY Step-by-Step Porsche 911 Guide

[356RS]

Originally Posted by MY911S

I actually thought about doing it very similarly as this:
Technical Tips - The Home of the DIY Step-by-Step Porsche 911 Guide

Yes you are on-track. This is the best way to remove the frozen plungers. Removing the camshaft will make this a lot safer. Damage to the bottom of the plungers/camrollers can occur when the camshaft is left in. I also use a hardened wood drift to tap out the plungers if there are not to tight in the cylinders.

[MY911S]

Thanks Mark!

[MY911S]

Got my plungers unfrozen basically using the above technique. Now I have to do the same with the rack

[356RS]

Did you remove the flyweights, space cam and the camshaft so you could remove the plungers? If the main rack is still frozen or very hard to move you still have plungers that are binding/draging and that will affect the rack movement. I have never seen just the main rack frozen. Plungers mess-up up the main rack movement.