MFI Pump - Open Heart Surgery

[michel richard]

Fantastic thread, I agree.

And thank you for the space cam picture.

Michel

[Jeff Higgins]

Well, I ran the car on our local chassis dyno last Wednesday. Here is the resultant chart. The upper graph shows horsepower and torque; the lower shows A/F. Note that this is full throttle only. It does show the typical (for MFI) tendency towards leaning as rpm's climb. In light of that, I did fatten it up a bit from my last LM1 runs, to ensure adequate fuel at higher rpm's to avoid detonation.



The motor is essentially a stock '83 3.0, save for the conversion to MFI, JE 9.5:1 pistons, and some custom cams from John Dougherty ("camgrinder" here on Pelican). The throttle bodies and stacks are 36mm "S" and the exhaust consists of SSI's and an old Leisritz sport muffler. The intake ports were opened up to 38mm and MFI ports drilled by Monte Jarvies up here at Redmond European. I'll do a full write-up on the motor on another thread.

[356RS]

Jeff, The information that you have shared with all of us has taken so much of the mystery out of the MFI pump. Thank you for all the time and energy you put into this thread.

[beepbeep]

Wow!

I never had any MFI car but I must say I really enjoyed reading this thread and understanding how that little mechanical fuel gadget works!

LM-1 is really a nice tool and a must when fiddling with fueling. Be it MFI or EFI...it's little "pocket dyno". AuxBox that logs RPM, MAP, AFR and accelleration can be even used to optimize the ignition, once fueling is in check. It's a matter of doing repeatable pulls and comparing the graphs. Accelleration is proportional to torque, and power is torque x RPM. Once you have maxed torque, you have maxed the power as well

Anyway, great stuff and pleasure to read!

[rswannabe]

Jeff,

I had heard you had broken the code of MFI tuning, but only just now had the time to read this post. To you and all those who contributed to this thread, I have this to say:


BRAVO! BRAVO! BRAVISSIMO!!!

['71 911E Coupe]

Jeff,

Great to hear that you know for a fact that you have achieved your goal with the air-fuel ratio.

You weren't lying when you said a lot of oil is down in the bottom of the pump. I took the idle screw cover off today because the idle screw would not push in or turn at all. I was replacing my alternator today anyways so I had more angles to get my hands in there. I put a bunch of rags down to catch the oil and boy they got all soaked up.

The main idle screw is out past the pieces of metal next to it, and I have not ever adjusted that since I've had the car. I'm guessing this means its really leaned out at idle??? Maybe this is true cause I think it is running a little to lean at idle and I tried doing what Jeff did and used the part load to compensate for it and was going through fuel way to fast. So I guess I should screw it in a little bit. Maybe later on I'll mess around with the white and black screws, but this thread has helped me with this case. If this thread did not exist, I wouldn't have even tried to take that cover off.

[Mr9146]

Good work, Higgins. I'm extremely impressed with the work you've done on your car since our initial conversations in SLO. Can't wait to see her in person once again.

[kenikh]

Originally Posted by jcge

From what I can tell based on discussions with some Mercedes Benz guys (and please dont take this as gospel !!!) the internal adjustment screws on EP/RLA regulators are located on the

1) Rack head (overall adjustment) - internal adjustment
2) Caspule - centre screw - idle adjustment/CO - accessible without disassembling the pump.
3) Capsule - 2 x black screws 450-1000rpm (pump rpm)- internal adjustment
4) Capsule - 2 x white screws >1000rpm (pump rpm) - internal adjustment

The screws and springs in the capsule control the amount of fore/aft movement of the space cam with changing engine speed. The throttle control lever provides the rotational position of the fuel map



The picture clearly shows the center (CO) screw and the 2 x white (low speed) screws - the 2 x black screws are too black to see, but are the remaining 2 screws on the capsule head

Heres the screw on the rack head for the "overall" adjustment (top of image - it also shows the position of the capsule between the flyweights of the governer.



I'm sure it would all be explained in the Bosch document VDT-WPP 711/1B....anybody care to share a copy ???

Note that some racing pumps use modified flyweights (lightened) to further alter the relationship between pump speed and space cam fore/aft movement.
This ones from a 935 pump (c) B.Buschen.

Jeff did you ever edit this? I thought you found the adjustments to be the opposite of this?

[Jeff Higgins]

I found this part to be accurate:

1) Rack head (overall adjustment) - internal adjustment
2) Caspule - centre screw - idle adjustment/CO - accessible without disassembling the pump.
3) Capsule - 2 x black screws 450-1000rpm (pump rpm)- internal adjustment
4) Capsule - 2 x white screws >1000rpm (pump rpm) - internal adjustment

This part contradicts the role of the white screws stated above, and is incorrect:

The picture clearly shows the center (CO) screw and the 2 x white (low speed) screws - the 2 x black screws are too black to see, but are the remaining 2 screws on the capsule head

It should read The picture clearly shows the center (CO) screw and the 2 x white (high speed) screws - the 2 x black (low speed) screws are too black to see, but are the remaining 2 screws on the capsule head

[jcge]

Edited the original post to make this correction

Regards
John

[Roland911]

Hi Jeff,

I had similar problems.
I never understood 100% why it is not possible to make such fine-tune adjustments apart from the main idle-/ and part load screw adjustments.
Nobody could help!!
4 years of pain are over.

THANKS!!!

Even in Germany (apart from Koller & Schwemmer) nobody has the knowledge.
And K&S is apparantly making a secret out of it.

Roland

[Jandrews]

*** Specific Picture Request ***

I thought I would use this great thread to request a specific picture of the MFI system. Jeff, or someone else, do you have a picture of the "back" of the idle speed plate that houses the sprung adjusting "bolt"? In looking at your pictures, the internal piece on the governer that gets engaged by the sprung idle adjustment bolt is clearly a hex-sided slotted screw. What I am looking for is the part on the back of the sprung adjusting bolt that actually engages the slotted screw. In other words, when you gently depress the spring on the exterior bolt for idle mixture adjustment, what happens internaly to engage the slotted screw? Is there basically a slotted screwdriver on the back of that adjusting bolt?

Does my question make sense and describe what I am looking for?

Thanks,

JA

[356RS]

JA,
Yes, that is exactly what is on the other end of the spring loaded adjuster. A small screwdriver head that fits into the slotted hex screw head.

[jcge]

Picture showing idle CO adjustment screw in the center (10a ) and interaction with the capsule via the spring loaded adjustment screw (10b) at the rear of the pump governor

(picture from Mercedes Benz, but identical internal equipment used by Porsche. Ignore the "t" bar screw (actually a dipstick) and large hex nut in the picture - they are just parts of the rear pump cover in the Mercedes)


(C) Mercedes Benz

Rough translations...

10a Adjusting screw (black) for no-load (idle CO) operation until approx. 1000 engine revolutions
10b Spring loaded adjustment knob (idle CO)
11a Adjusting screws (black) for part-load and intermediary number of revolutions area from approx. 700 to approx. 4000 engine revolutions
11b Adjusting screw (white) for part-load and upper number of revolutions area starting from approx. 2000 engine revolutions

Pushing the spring loaded adjustment knob (10b) in and turning engages the flat "screwdriver" head in the idle CO adjusting screw (10a)

The cover plate needs to be removed to access the other screws.

Regards

John

[michel richard]

So that according to this document, there is some overlap in the 2,000 to 4,000 engine rpm area . . . the black screws having an impact from 700 to 4,000 and the white from 2,000 to redline.

This is interesting.

Fantastic thread, I agree !

[Jeff Higgins]

Great information, John. It's nice to see verification from a published source. It is really nice to see that they acknowledge some overlap in the adjustments; it really has to be that way to work in a progressive manner.

Anyway, I've been busy since I last visited this thread. There have been some changes to the motor; it is now twin plugged with a bit more compression. Here is the dyno chart generated three days after I got it all back together. A/F was measured with both the dyno shop's equipment, and my LM 1 concurrently. They agree within less than 1/10 of a point.

[jcge]

Great to hear you have good correlation between your LM1 & dyno AF numbers...another vote of confidence for the LM1 and your pioneering work in tuning your MFI "on the fly".
Regards
John

[Phoffren]

Great job in all facts
I have follewed this messageboard for several years
but only now joining in


Now for deeper knowledge, has anyone find out the dimesions of the space cams in diffrent variations?
I have six pumps on stock
2pcs of ....005 (69S)
one ...013 (72S) on my car
one....009 (70S)
one ...014 (72E)
one ...014 modifided for euro 2,7 rs engine spare for my 72 s

I have the ...005 on my workshop to opened and i have plans to make a 3-D modellin out of the space cam of it

On my knowledge is that 69-71 space cams are narrower than the 72-73 ones? is this correct information
and is the widernes the only main measurement which varies in cams or also the shape of the surface?

Sorry about a little bad english



Best Regards
from Finland

Pekka

72 2,4S
71 2,2T
70 2,5 (R replica)

[jcge]

Here are the two different widths of space cams (no dimensions sorry..) Early model on the left - narrow - (2.0L, 2.2L & factory racers) uses a roller type follower, later style on the right - wide- (from 2.4L & 2.7L motors) uses a ball stylus type follower (other differences exist too in the internal transmission ratio to the rack)



Each cam has a different surface profile to match the air flow characteristics of the specific engine. Here's a development map from a mercedes benz engine (220er)

]

And links to space cam part numbers by model & application

Porsche MFI

[obrut]

Jeff,

Firstly, let me add my thanks to those already offered.

Secondly, you mentioned going back and making some corrections in the thread regarding the function of the black and white screws.

Can you please confirm that this para is correct:
"So, in a nutshell: White screws to adjust high rpm full throttle delivery. Black screws to adjust low to mid range full throttle delivery. Part load (main rack) to adjust, well - part load at all rpm's. The center idle screw for - wait for this - idle. It all makes sense now. It is all predictable and repeatable. "X" number of clicks on the white screws affect the high end A/F ratio by "Y", and so on for the black screws and the idle screw. The role of the "part load" is what clouded the matter for me. I had been shown to, and always used it as a "high speed" adjustment. It most decidedly is not."

I'm currently battling a very rich 1000-4000 rpm condition. Am I correct in thinking my first adjustment is to back out the black screws?