MPS- delving into it's secrets?, Update January 3, 2011 Options

[jk76.914]

So if Bosch does a rebuild kit over a complete rebuild I've got buy a AFR and a laptop, cut holes in my exhaust, and learn to weld? Or, I guess I could buy a rebuild kit and then try to find a mechanic that knows Djet and is willing to do the tuning at a reasonable price.

Ugg, doesn't make sense for 95% of the 914 owners out there.

It'd never be an either/or. Bosch would never do a rebuild kit only over a complete rebuild. So you'll never have to face this situation.

[Bleyseng]

Even when Bosch comes out with a new or rebuilt MPS, everyone should do as Brad suggests..put it on a dyno and check your AFR at part load and WOT.

of find a friend who has a LM1 to check it.

The original MPSs were set up for brand new engines off the VW line. No one has a brand new engine, most rebuilds are mostly new or reconditioned parts..and who has brand new injectors, fuel pump, etc.

[3d914]

Any update on this? Curious 914 owners are watching!

[jk76.914]

Any update on this? Curious 914 owners are watching!

Not much at the moment from me. I'll get back into this this winter. Rebuild of my front end will pre-empt much else for a while, though.

I was able to confirm presence of Be in my stock diaphram, using EDS at work. That's Energy Dispersive Spectroscopy. Like XRF, it also can't determine component %-age in an alloy for elements below atomic number 5 or 6, because it also depends on X-ray. The only way I've found is a "wet" process, where the sample is dissolved in nitric acid, then separated somehow into component elements, and measured. I haven't pursued where I could get this done, or for how much. But at least this is confirmed this to be a beryllium alloy. Probably any of a couple of the Brush-Wellman sheet stocks would be suitable.

Also, since I have several "good" diaphrams to work with, and I've characterized their ranges of adjustment, I'll be concentrating on how to tune them to my engine. In May, I replaced the original muffler on my Bursch system with a much quieter one, and added an O2 sensor bung. I have a lambda meter from PLX devices ready to install, along with 1K pot to replace the ballast resistor, and some assorted other parts. I'm thinking of making up a console where a co-pilot can tune some settings on the road, even (potentially) simulate an MPS with a variable inductance to establish "ideal" curve for my engine. Then see how close I can come to mapping on on the bench. Getting all the way through this process is my goal for next summer- after the front end is done.

I'll update from time to time along the way.

[trfrick]

This is what I received from Bosch regarding rebuilding 041 MPS:



The refurbishing of a 0 280 100 041 will cost 349 EUR gross (incl. 19% German VAT) plus shipping costs.

If interested please send the MPS to my hands:

Robert Bosch GmbH
Matthias Klumpp (AA/ATR)
Auf der Breit 4
76227 Karlsruhe
Germany

I will then forward the part to our plant where the refurbishing is done. Please contact me again so that I can send you a so called "pro-forma invoice" for customs duty. Shipping should be done by TNT Express.

-> If the part is not repairable you will get it back unrepaired.
-> If it's okay (within its tolerances) we will bill you with examination costs of 19 EUR.
-> If it's defective but repairable you will have to pay the refurbishing costs by buying a special item in our eBay store http://stores.ebay.de/Bosch-Klassik-Teilvermittlung - you can pay via PayPal or via bank transfer. The refurbishing will start once the money has been transferred.


P.S.: If you have a VAT ID we can create an invoice without sales tax.


Mit freundlichen Grüßen / Best regards

Matthias Klumpp

Robert Bosch GmbH
Automotive Tradition (AA/ATR2)
www.bosch.com
www.automotive-tradition.de
stores.ebay.de/Bosch-Klassik-Teilevermittlung

Tel. +49(0)721 942-1660
Fax +49(0)721 942-2000
Automotive-Tradition@de.bosch.com

Sitz: Stuttgart, Registergericht: Amtsgericht Stuttgart, HRB 14000;
Aufsichtsratsvorsitzender: Hermann Scholl; Geschäftsführung: Franz Fehrenbach, Siegfried Dais;
Bernd Bohr, Rudolf Colm, Volkmar Denner, Wolfgang Malchow, Peter Marks,
Peter Tyroller; Stefan Asenkerschbaumer, Uwe Raschke, Wolf-Henning Scheider

[r_towle]

fantastic news

[jk76.914]

Well, I guess it's time to get back at this. Here's my plan for the near term-
- make some new gasket sets on a laser cutter. I have a sheet of .100" neoprene, and I'll try cutting out the big ring seal and the smaller ring that goes around the outer adjustment nut. Then I can assemble a test MPS using one of the diaphrams that gave a lot of adjustment range, with no leaks (fingers crossed).

- I'm going to try and set up to map vacuum vs. lambda on the fly. I've been thinking about this all summer off and on. I picked up a Pico Technology PicoLog 1012. This is a data logger that plugs into, and is powered by a USB port in a laptop. It actually has 12 channels, but I only will use 2. One channel will be connected to the linear output of my PLX AFR sensor module. This outputs a voltage from 0-5vdc that is proportional to AFR. This is one of the reasons I got the PLX. The second output will log vacuum. To do this, I still need to buy a GM MAP sensor. These were used in many GM models in the early to mid-90's, and they output a voltage 0-5vdc that is linear with manifold pressure from 0-1bar. (There are also 2 bar and 3 bar versions for turbo applications, but I only need 1 bar and they're cheaper- about $35).

I got set up for this with the purchase of the PLX (actually a Christmas gift that I haven't tried out yet, 50 weeks later), and the install of my Walker SS muffler on my Bursch exhaust that I documented in another thread last May While I had the muffler welded up, we installed the bung for the O2 sensor.


I'm thinking the only thing left is the GM MAP sensor, and then hooking it all up.

The data logger came with software that I can set up to capture data (voltages, actually) from both channels simultaneously at pretty much my choice of speeds. It can only capture 8000 data events in it's memory, across both channels, so I'll probably start with 100 events/second, which will give me 40 seconds of data. So as I drive down the road, I'll have someone else with the lap top who can download the data once every 40 seconds or minute or so, and then start collecting again.

The raw data can be downloaded into Excel, and then plotted as a scatter diagram. I'll plot each point with X axis as voltage from the MAP, and Y axis as voltage from the PLX. I expect that as I move the throttle, the points will be all over the place because there is a lag between when the vacuum changes (throttle opens or closes) and the AFR settles in to the new point. But if I drive smoothly, with constant throttle, they should cluster about a horizontal line that roughly represents AFR at each vacuum level. I'll vary speed and even gears to get 40 second long samples at various loads.

By overlaying the calibration curve from my MPS, I can visually see where the MPS curve needs to change to bring lambda better into alignment with desired. The work I did mapping MPS adjustment ranges will feed into my selecting the right diaphram and setup to tune the whole thing in iteratively.

At least that's plan.

[jk76.914]

I've set aside trying to make diaphrams for now. Since they're available in rebuilds from Bosch (albeit at big $$), or can be harvested from 1.7 MPS's for a bit less, the common problem now seems to be how to tune the MPS to a specific engine. Whether it's a new MPS, a good used one, or a rebuild, factory settings are at best a compromise. Our engines are old and worn, or rebuilt with tweaks from original. Even a newly blueprinted engine should have it's MPS checked, because even original factory settings were a compromise in the first place.

I had a scheme where I would use a Type 3 MPS (no diaphram, only aneroid cells) as a slave, and measure vacuum level that resulted in desired AFR. This could then be translated into inductance to plot desired MPS curve. I think it would have worked, but it would have been very awkward. Then I hit on this idea.... We'll see.

[jk76.914]

I also toyed with the idea of making a test diaphram out of the sheet neoprene. It would have been an interesting experiment, and I'm sure it would have worked, at least at high vacuum and low vacuum, but I had no idea how it would behave in the transition region, or the impact of temperature or aging.

If I do decide to dabble in diaphram fabrication again, I'm sure this will be my first try. Just to find out.

Bung with sensor-

[jk76.914]

Here's a loose end from last spring. I dissected that riveted, non-leaking Volvo MPS to find a pristine diaphram. But I never showed the adjustment range, so here it is. It beats any other diaphram I tested-

[SirAndy]

I've set aside trying to make diaphrams for now.

Too bad. That's the one item that could help a lot of people keep their original FI ... (IMG:style_emoticons/default/popcorn[1].gif)

[Bleyseng]

Here's a loose end from last spring. I dissected that riveted, non-leaking Volvo MPS to find a pristine diaphram. But I never showed the adjustment range, so here it is. It beats any other diaphram I tested-

Wish you would make em like this! They have better transition than any of the other made.

[jk76.914]

I know. Something had to give. If I focus on making new ones somehow, I don't get my car "finished" for a while. I'm 58, and I've set an objective of having it "done" by the time I'm 60. (I started taking it apart when I turned 50, btw, after owning it and driving it for 20 summers.) So I only have 2 summers left to meet my goal. Figuring out how to tune it to a specific engine (mine, for now) helps me get there, while tooling for a new run of diaphrams doesn't. So that's the story.

I'm mulling over how to get diaphrams from Bosch. Doesn't seem right that they have them sitting over there in bins while our 35+ year old ones are dying one-by-one....

[Bleyseng]

I know. Something had to give. If I focus on making new ones somehow, I don't get my car "finished" for a while. I'm 58, and I've set an objective of having it "done" by the time I'm 60. (I started taking it apart when I turned 50, btw, after owning it and driving it for 20 summers.) So I only have 2 summers left to meet my goal. Figuring out how to tune it to a specific engine (mine, for now) helps me get there, while tooling for a new run of diaphrams doesn't. So that's the story.

I'm mulling over how to get diaphrams from Bosch. Doesn't seem right that they have them sitting over there in bins while our 35+ year old ones are dying one-by-one....

What, that's your car and its not done?
I am 58 too and miss driving my car and can't decide if I want to ship it to Suriname. There are few twistys here but there are the Saturday night drag races!

[realred914]

Wow, really great info! With your permission and credit to you, can I use some of the photos and data on my MPS page (see link in sig)?

You mention the full-load diaphragm provides altitude compensation. This is only true under heavy and full-load conditions. The only MPS's that provided part-load altitude compensation were the 0 280 100 100 series that was used on the MB's. These units lacked the full-load diaphragm (full-load was sensed by the throttle switch) and had an altitude compensation cell that was connected to the atmosphere through a holow screw.

I agree with your observation that the lower the "stiffness", or spring constant of the diaphragm, the less effect it will have on the transition characteristic. For any material used, the thickness and pleat design will vary. Reliability and resistance to fatigue failure is also an important consideration in the material selection.

Crafting the aneroid cells out of a different material and/or a different pleat design would be tricky. The issue here is to identically duplicate the pressure vs. displacement characteristic of the OEM cells. It would interesting to compare the SS cells to the OEM cells for this characteristic.

Positioning of the full-load stop is also critical to defining the transition region, setting the proper full-load mixture, and reducing the mechanical stress on the full-load diaphragm. Bosch sets most MPS to a 2 in. Hg engagement, though I have seen some units set to 4 in. Hg.

Again, great stuff, thanks for sharing it with us.

On the data and photos- you're welcome to them, with one caveat. We're using beryllium in a project at work, and one of the characteristics is that it is transparent to X-rays. So I need to verify that our XRF is capable of detecting Be in alloys. If not, those numbers may not be right. I'm travelling until the end of the week, so it'll be Friday before I can get with the lab guy. We have other means of measuring alloys that I can pursue that don't use X-Rays. The brass and stainless alloys should be correct.... Sorry to everyone if my info was premature. I'll be sure to confirm or correct it shortly.

That makes sense about the full load only altitude compensation. The diaphram has to lift off the stop for any compensation to occur.... makes sense. I have a 0 280 100 120 MPS from a Cosworth Vega that is like the MB MPS you described... but then it is, as you said, part of the 100 series... Interesting that Chevrolet licensed the technology directly from Bendix, not Bosch, but all the comonents are Bosch.

I measured several (maybe 6) aneroid cells sets using the same MPS, but with the diaphram locked. I set their inductance to a common value at the same vacuum, and then measured and plotted the curves. Their slopes are identical. I plotted them on the same axis, and they are as coincident as I can imagine. These 6 included a set from a 0 280 100 001 (early type 3, no diaphram, probably the simplest MPS out there) AND the stainless steel set.

So now I'm setting up to measure the vacuum/L curves for diaphrams alone. I sacrificed a set of perfectly good aneroid cells by cutting them open and filling them with gorilla glue to set them. I let them harden in my vise with the jaws set to original cell dimension (gorilla glue expands when it hardens, and would have pushed them open). First thing I found was that the cells ARE MANUFACTURED WITH PARTIAL VACUUM INSIDE!! As soon as my cutoff blade broke through, they expanded out and became flacid. Anyway, now that they're hardened up, I'm going to measure inductance curves, which will represent the response of the diaphrams alone.

I'm thinking that I can combine the diaphram and cell responses using superposition and get pretty close to what the finished MPS should be.... getting interesting.

if the x-ray window in your instrument is made of berilium, detecting berilium is out of the question.

[realred914]

looks like i will will be needing to get my mps claibrated soon with teh new 96 mm motor getting built for me.

a wide band O2 sendor seems like a nice way to adjust it by.

i may end up doing this too.

i have mapped four mps untis. me and a friend had using a vacuum pump, gage and a henry meter, each was different, some strikingly so.

the thing is we never tested it otehr than by seat of the pants, so that got me thinking of an O2 sendor, i used on on a triumph for tunning a carb, tricky but doable, it should be fun (IMG:style_emoticons/default/icon8.gif) with the multible screws to turn on the MPS !!!

any advice on which screw does what and so forth when adjsuting?

[jk76.914]

looks like i will will be needing to get my mps claibrated soon with teh new 96 mm motor getting built for me.

a wide band O2 sendor seems like a nice way to adjust it by.


any advice on which screw does what and so forth when adjsuting?

I recommend Brad Anders articles on the D-Jet at http://members.rennlist.com/pbanders/manif...sure_sensor.htm

That will tell you which screws to turn and so forth. There are other adjustments outside of the MPS though-

- fuel pressure. It MAY be interesting to try a regulator that is modulated by manifold vacuum. I'm curious if it'd be possible to use a diaphram-less MPS that is properly set up with such a regulator. That'd be a great way to solve the diaphram availability and reliability issue! Later applications did exactly that- Mercedes and Cosworth-Vega (OMG!) to name two.
- ballast resistor value.
- timing- definitely affects vacuum, and anything that affects vacuum affects MPS and therefore AFR with D-Jet

Some or all of these are documented in other threads by others here at 914world.

As far as MPS is concerned, the mapping I've done with each of these various diaphrams evaluates the range that they can be set within, by pre-biasing the diaphram towards or away from the coil to max limits of the adjustment. As you can see, the pristine stock diaphram has a very w-i-d-e range available. I'm hoping to see where within that wide range is best for my engine.

When I get my data logger running, I should have a visual tool to see what's going on across the range of vacuum the engine sees, and I can try these ideas, one variable at a time...

[914 shifter]

diaphram-less MPS that is properly set up with such a regulator.this sounds too easy.i hope that someone has success with this idea (IMG:style_emoticons/default/chowtime.gif)

[bandjoey]

Yes. I've just read this front to back and it's interesting as hell. But, can anyone tell me why salt makes the ice colder when making ice cream! (IMG:style_emoticons/default/happy11.gif)

I'm also thankful we have a community of scientific types to do this work. It's on the track of keeping our cars on the road. Original parts are getting too $$$ out of hand from mfg's like Bosch. THANKS (IMG:style_emoticons/default/first.gif) First Class Work.

[Bleyseng]

if you are running a stock rebuild motor setting the MPS via a Wavetek is the easiest way and works. We have the known settings for the Wavetek to do this.
if you are running a non stock cam you must adjust the inner and outer screws for the proper AFR and slope, then set the WOT stop screw for the WOT AFR (12.5 to one). Using a LM1 hooked up properly doing multiple runs is the only way I know how to do this. On a roller dyno or on the road works fine.