MFI Pump - Open Heart Surgery

[Jeff Higgins]

I had an interesting conversation with a buddy and very well respected local race car wrench over dinner and beers last night. We were talking about my (finally running) 3.0 liter MFI motor, and my efforts at dyno tuning it. Essentially, it runs too rich between 3,000 and 4,000 rpm, with the high and low speed mixtures spot on (all dyno verified).

I think I need a different space cam. He tells me there are actually adjustments inside of the aft cover, the one that goes over the space cam and clamshells, that may correct this for me without having to change the space cam. Apparently the one outside low speed adjustment and the high speed one under the cap screw are the the ones Bosch trust duffers like us to make; they hide the other ones inside where only the experts can find and utilize them.

So, the question of the day is this: have any of you fooled around with these adjustments? Any sage advice (other than "don't")? I have two extra pumps just sitting around, one functional and one siezed. I'm going to take one apart and see what is in there before I risk the one running on the car. Does anyone know which adjustments do what?

[Rot 911]

I personally don't know. I would call Gus at Pacific Injection and ask him.

[304065]

It's too fat during a 1,000 RPM band but OK at the top? I would leave it alone.

Most MFI pumps run lean at the high end, so if yours is OK, I wouldn't upset the balance. A little fat we can live with, what is the AFR?

To answer the question, I am not aware of any internal adjustments, nor does the MFI repair manual mention any that would correct that single area. You might be able to move the whole fuel curve up or down, but I dont' think there's anything specific.

[David E. Clark]

Jeff,

I am not aware of any internal adjustments (or any other turn-screw adjustments for that matter) that would effect only a specific RPM range. I've heard early racers would substitute different shaped cams to get better performance at different RMP ranges to give them advantages for passing on certain tracks but as far as I know that type of "adjustment" is way, way beyond what a "duffer" should attempt. I second the advice to get in touch with Gus at:

Pacific Fuel Injection Service
153 Utah Avenue
South San Francisco, CA 94080
(650) 588-8880

If anyone would know, he would. Perhaps Grady Clay will see and respond to this thread. He's got more MFI knowledge that the rest of this board combined! If you figure this out, please post your conclusions.

[David E. Clark]

Jeff,

You might find some help in the publication called Bosch MFI Repair Instructions, Supplement 2. Some adjustments are apparently available on the Porsche 2.4 engines which change the relationship between the 3-D cam and the follower lever which modifies the mixture control governor. This in turn seems to effect the mixture to different degrees at different RMP levels. The instruction is beyond my level of expertise. I don't know what specific changes you made to adapt your pump to a 3.0 motor but this technique may be adaptable to your pump. According to the manual, these adjustments require an "adjustment bushing ... which is inserted into the bushing of the measuring ring." You are a better man than I if you have all the necessary tools and can follow these directions! Good Luck!

[Jeff Higgins]

Thanks, guys. I spent my lunch hour perusing all of the Bosch MFI manuals and parts diagrams over on the tech info page. I can't find any internal adjustments, either. I'll see my buddy again on Saturday (I hope) and grill him a bit more. He is a 935 mechanic (had a couple of cars at Rennsport and Monterey, the white "BP" and the yellow "Road Atlanta" liveried cars). He may be thinking of something unique to 935 pumps.

John, I have the idle A/F all the way down to 14:1; about as lean as this pump will go. The high speed mix goes as lean as 13:1 at 6,000 rpm (as high as I wanted to take my new motor just yet). Off-idle to about 2,800 rpm runs acceptably, in a gradually richening progression from the idle 14:1 to about 12.5:1 at 2,800. Then it takes a real dive into the mid-range fat spot that occurs between 3,000 and 4,000 rpm and goes as rich as 10:1. Once over 4,000, it rapidly recovers to about 12:1 before it begins that typical high rpm progression towards ever leaner. This is at full throttle, mind you, and I'm really not sure there would ever be a reason to "floor it" much below that 4,000 rpm spot. Part throttle in that rev range runs about 11:1; still not great, but better. I have put about 400 miles on it in the last week and honestly cannot detect the rich condition anyway.

Looking at the A/F charts sure gives a graphic representation of where the space cam kicks in and "does its stuff", then when it finally becomes ineffective at 4,000 rpm. I'm kind of guessing here, but the A/F chart seems to show the pump delivery being governed by the low-speed adjustment up to just below 3,000 rpm. The high-speed adjustment seems to kick in about there, with the space cam fighting to keep it initially lean, until the air demands catch up to the "perceived" (by the pump, through its main rack position) fuel demand.

It's quite revealing to see the mix make such rapid changes as various parts of the governing mechanism kick in, and then quit. "Reading between the lines" screams "new space cam"; one that will lean the mid range out more. Which makes sense, considering there is a "T" cam in it now. With the lowest high-speed fuel requirement of the bunch, the "T" space cam probably has the least affect on rack position in the mid-range. I would imagine T, E, and S motors would all have similar part-throttle and full-throttle fuel demands in the mid-range. The S, with its far greater fuel demands at high rpm's, must have the most "aggressive" space cam, to push that main rack further from its richer high rpm setting and down into an acceptable range for a mid-range mix. So, I think that is what I need. My 3.0 liter has even greater high speed fuel requirements, so if I back that high end screw out enough to meet them, the space cam has to deflect the rack further to achive an acceptable mid range. Make sense?

Edit- Dave, I looked at that supplement for the 2.4 pump, along with the drawing of the adjustment bushing. Not quite as simple as turning mixture screws, that's for sure. I would have to have one made, then figure out how to use it. Probably beyond me as well...

[69911e]

I believe there are two adjustments which will affect the relationship between the cam and rack movement.
One is the adjustment for the thermostat. This one but may be what your friend is thinking of as it is internal only. I believe this will do similar things as the pressure sensor adjustment below.
The other is the shims under the barometric pressure sensor. I need to change this to get my car to run right (2.7 with E cams). If I remember correctly more shims will increase the gain of the cam compensation. Think of this as making the fuel delivery curve steeper.

[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 (high speed) screws - the 2 x black screws (low speed) 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 Higgins]

Good stuff, jcge. By the way, "B. Buschen" is my friend Bernie, the guy I have been having these conversations with. Very knowledgable, local R Gruppe member, and all-around good guy.

[jcge]

Originally Posted by David E. Clark

You might find some help in the publication called Bosch MFI Repair Instructions, Supplement 2.

The column titled "Adjustment" refers to "Spring" to affect the necessary adjustments in the Control spring pre adjustments and Part throttle settings. The "Springs" that these refer to are acted on by the Black and White adjusting screw pairs.

[jcge]

Jeff - Bernie's photo essay on pbase provides heaps of insight into these pumps, if your prepared to stare at the images long enough....

I don't know Bernie directly, but if you're in contact with him, I'd love to see a few more images of the boost pressure compensator on top of the 935 pump....an interesting addition for turbo cars..I assume is adapted from some other Bosch diesel application, but I've not been able to find any other info on its origin - I've seen it in 935, 917T and the "baby" engine photos

[David E. Clark]

Originally Posted by jcge

From what I can tell based on discussions with some Mercedes Benz guys ...

First of all, thanks for the great information. I can see how these adjustments are made for the Bosch pumps used on Mercedes engines but I can find no reference to these same adjustments being available on the Bosch pumps for Porsche engines. Below is the only reference I can locate and it appears to be specific to Mercedes. Do you have any reference to doing this on a Porsche? I'd love to have a copy.


© Harold T. Glenn, Glen's Diesel and Gasoline Fuel-Injection Manual, page 5 (1973). Posted here for educational purposes only.

[jcge]

David - nothing specific to Porsche...as I said, my info was based on Mercedes...but they are the same regulators....the same capsule and screw set exist in the MB and Porsche versions. The adjustments are specific to each model - as per your spec sheet in the previous post.

The MFI repair manual on you ultimate resource page refers to the Test Instructions VDT-WPP 711/1B (ref Section 3.0 Inspection & Repair)- which details the "how to" of these screw settings - but I don't have a copy. This is THE document used to set up the pump on the pump dyno - (in conjunction with individual pump spec sheet) the "missing link" to all of the collective Porsche MFI documentation.

MB pumps were PES6KL70 series (that is single inline with 7mm plungers vs the Porsche PED6KL60 series - dual inline with 6mm plungers - except for the 917 which used the 7mm elements and boost pressure compensator. 1000+HP requires a fairly high fuel rate !!!

edit - just discoverd there were 7.5mm plungers as well - used by MB 6.3L V8 and Aston Martin V8

[jcge]

On ebay right now is a spare pump for the "baby" turbo engine (from a fellow Pelican)
I note its pump tag is PES6KL60/120 R1Z.....circa 911E2.0 ??
Doesn't show a tag for the Regulator section - think it would look something like EP/RLA 1-VXXXX

Sorry Jeff - didnt mean to hijack your thread - hope some of this discussion helps

[jcge]

Here's the back end of a 911E pump (R1Z)

Note the white screws, black screws and center CO screw - just as per the Mercedes scan David posted above.

Also the flyweights are standard - compare to the lightened 935 flyweights of earlier post

[Jeff Higgins]

jcge, I'll ask Bernie about some 935 boost compensating system photos next time I see him. I don't know the driver (Woody) at all, but Bernie and I were having a little "question and answer" session behind his white "BP" 935 one day at a SOVREN race. Bernie was explaining that particular system to me. He spends a lot of time with that car, so I'm sure getting some photos wouldn't be a big deal.

I pulled the nose piece with the low speed screw off of both of my spare pumps last night. Sure enough, the black and white screws shown above were right there. What is notable is that they were very clearly screwed in to different depths on the two pumps. Being a rather anal half German myslef, I'm pretty sure that's not just sloppy assembly. They are setting a baseline cam position or something with them. Take that big snap ring off in the above photo and the carrier with those five screws comes out, followed by what looks much like a double valve spring accompanied by a smaller inner spring on which the low speed screw bears. I'll play around with them some more and see if I can figure out what is going on with them. Or I'll just stick one in my pocket and head to Bernie's...

[356RS]

I'm all ear's on this thread. Very helpful information Jeff.

[David E. Clark]

Originally Posted by jcge

... The MFI repair manual ... Test Instructions VDT-WPP 711/1B (ref Section 3.0 Inspection & Repair) ... details the "how to" of these screw settings - but I don't have a copy. This is THE document used to set up the pump on the pump dyno - (in conjunction with individual pump spec sheet) the "missing link" to all of the collective Porsche MFI documentation.

Anyone have a copy? There are lots of MFI folks that could really benefit from this document. If someone can send me a copy, I'll make sure it gets posted in the Ultimate MFI resources thread.

davidedwardclark@yahoo.com

[Jandrews]

Subscribed

[jcge]

Originally Posted by Jeff Higgins

jcge, I'll ask Bernie about some 935 boost compensating system photos next time I see him. .....I'm sure getting some photos wouldn't be a big deal.
...
I'll play around with them (edit - the screws) some more and see if I can figure out what is going on with them. ...

Jeff - thanks a lot - photos would be great !!

Back to the screws and flyweights....(more particularly the lightened flyweights of the 935 photo)

Lightening the flyweights will have the effect of extending the rpm range of the pump - the lighter the flyweights acting against the standard springs, the higher the pump shaft speed required to progress the space cam from its idle to redline position (not to be confused with closed throttle vs WOT)

I've seen a few posts on this forum that report the space cam as having no influence on injection volume beyond 4000 engine rpm (tell me if I've misinterpreted), but I don't think this is correct. The following document Y 428 904 601 for 911/72 motor (edit 2.8 RSR motor) shows non linearity well beyond 4000 engine rpm (maybe the reference is to 4000 pump rpm = 8000 engine rpm..)

.
(C) B.Buschen

I've not run up a flyweight assy at speed and verified that the space cam is at full travel at that speed (4000 or 8000rpm) nor do I currently have capability to do so. In any case I'd love to know the spec/drawing for the lightened flyweights.

Again - all observation/speculation on my part - I'm not an authority on this subject (but others on this forum are......)

Regards,
John