M70 DK feedback resistance material repair possible?

[shogun]

My wrenching buddy has an Alpina B12 E32 with the M70 engine. Idle is not the best, the rest is fine, nothing to complain about the power. We just finished re-sealing the intakes and re-setting the timing, new spark plugs, new fuel hoses in engine bay, new ignition wires, new ignition coils, new fuel pumps, new fuel regulators, fuel injectors tested, new engine ground cable, tested CPS, CID, MAF etc pp.
All is fine except the idle, it goes slowly up and down.
Having read about the throttle valves, we also cleaned them up as good as we could. But we assume the problem could be the black stripes of resistance material where the wiper makes contact with the resitance material, especially in that area where the wipers run most of the time, idle position.
MWrench writes:
The black stripes are resistance material that is deposited on a substraight. Attached to the throttle boy shaft is a set of wipers that make contact with the resistance material. The wiper position is preset at the factory. As the throttle plate moves, the wipers also move along the resistance material and the resistance value changes.
Major concern on this DK set is the amount of wear on the resistance material. When the wipers wear thru the resistance material, the resistance readings sent back to the EML will not longer be correct or may fluctuate wildly during throttle plate movement. This certainly would set off the EML light and may initiate “limp home” mode
More here, see especially the last pic http://www.mwrench.com/Whitepapers/DKMotorcleanup.pdf

Easiest would be to replace the throttle valves, we have plenty on stock, but that would be too easy, we would like to find a way to repair this area of resistance material.

Did somebody already do that? How? Which material and procedure?

Test procedure for the DK is on my website in German and English, someone on the German forum got these data from Bosch in Germany years ago, see http://twrite.org/shogunnew/topmenu.html reference data >>>>control systems>>DK input details, there is a small pdf file

[dragon850]

Shogun, this is what I specialize in when rebuilding the throttles.
It's the main problem with these DK motors, anyone can clean them up but that does not help when the feedback from the open encoder is wrong.
My approach is to move the encoder whiskers fraction of the mm at a time so they hit unused encoder surface then re test each time to see if the fluctuation was reduced till they are close to factory spec as possible.
It's a precise and time consuming procedure to say the least but it works.
That said throttles can be rebuilt this way only once, no replacement surface material works, I tried several, it's not hard enough and wears fast. I have commissioned an encoder manufacturer in the past to reverse engineer this open encoder design with the Bosch spec sheet you have in your post, after much back and forth it was not worth doing financially.

[shogun]

Thanks, the way you do it is exactly what has been proposed more than 10 years ago on the German forum and we have done that already on some DK's before to move the encoder whiskers a fraction of the mm at a time so they hit unused encoder surface.
That works, but I hoped meanwhile someone had found a solution to replace the surface contact material with a long lasting material.

[kce1900]

I have commissioned an encoder manufacturer in the past to reverse engineer this open encoder design with the Bosch spec sheet you have in your post, after much back and forth it was not worth doing financially.

How much money are we talking about here? Given that a single new DK costs around three thousand US dollars some people might be willing do dish out some good money for a reliable fix that makes an old DK as good as new.

[SergeBMW]

I am not sure what the resistive material on our DKs is made of, but could very well be a more basic carbon based material since it really just is a potentiometer. I am sure there must be a way to re-surface the carbon or whatever resistive material it is that they use. Proper resistance between the 2 ends would have to be crucial. That must be due to the compositon of the material.


Some info on resistive materials used in potentiometers:

Carbon composition

• Carbon composition ink molded on a substrate(phenolic resin). Most common material, low cost and reasonable noise and wear characteristics.

Wirewound

• Wirewound pots can handle high power,are long lasting and can be very precise. They have however a limited resolution and rough feel. Most used in high power applications (rheostats are often wirewound) or as precision pots.

Conductive plastic

• Very smooth feel and high resolution, can be constructed to perform millions of cycles. Can only handle a limited power and are expensive. Often used in high-end (audio) equipment where a high resolution and low noise are important.

Cermet

• Very stable, low temperature coefficient and handles high temperatures well. On the other hand quite expensive and often limited amount of cylces allowed(special long-life cermet pots also exist). Often used for trimpots which do not have to be adjusted often.
  

[kce1900]

Serge, here are links to two images showing the carbon part and the slider mechanism:
http://www.km5tz.com/images/850i/850iDK10.jpg
http://www.km5tz.com/images/850i/850iDK9.jpg
You can clearly see the grooves that the slider cut into the carbon. Attached are close-ups of those claws. Since these things are constantly moving, the carbon needs to be very hard. And since the sliders are quite solid, I'm curious how they could be moved or bent in order to run in a different track.

[RobertRO]

I wonder if it may be worth developing a turn-key kit, field installable by the car owners, which would convert from fly-by-wire gas pedal and DK motors to mechanical, cable actuated throttle bodies.
This approach would obviously also require certain changes in the ECUs, therefore a pre-tuned plug-and-play Megasquirt unit may be a suitable workaround.
Such a solution would bite into the originality of the car, but, as these cars age, it may be a cost-effective way to keep them in a good running and reliable condition.

[dragon850]

Re positioning the encoder whiskers takes time and alot of practice, you are going by feel and retesting the resistance for stability.
After doing this on 300+ pairs I have gotten damn good at it lol.
Cost to re manufacture the encoder was in the mold, we were taking about 20k plus, I did not want to spend this much the ROI would not make sense.

[shogun]

Here is a company which repairs Maserati wiper material carbon track with a contactless system: Fixing the Maserati's Throttle Body - Wheeler Dealers https://www.youtube.com/watch?v=w2FMq5DEvQU
The website of the company http://www.maseratished.co.uk/

[shogun]

anyone meanwhile contacted maseratished in the U.K., if they can do that for the M70 engine Bosch DK's?
I personally still have plenty of stock of M70 DKs for me and wrenching buddies, but for those which do not have, might be worth to start action.

[shogun]

someone from the German E32 forum contacted the company in the U.K., reply: "I'm sure that a solution can be developed, but, I only work on Italian cars, I'm afraid. Sorry. Yours, Mike Roberts www.maseratished.co.uk"
-----------------
looks like no interest in the development of this for the M70 DK

[kce1900]

Three weeks ago I looked that the "maseratished" video a bit more carefully and checked their website. I don't have the impression that they manufacture the part. Googling Maserati 3200GT Throttle Body led me to an eBay offer with some pictures that showed the name of the manufacturer in China: sacer. Apparently the same part has been used in many Volvo models.

At that time I also found a Canadian company that does similar things: xemodex. Since they have a product request form on their website, I sent them an email asking what it would take to start a project for the M70. So far no reply.

[rjjablo]

Three weeks ago I looked that the "maseratished" video a bit more carefully and checked their website. I don't have the impression that they manufacture the part. Googling Maserati 3200GT Throttle Body led me to an eBay offer with some pictures that showed the name of the manufacturer in China: sacer. Apparently the same part has been used in many Volvo models.

At that time I also found a Canadian company that does similar things: xemodex. Since they have a product request form on their website, I sent them an email asking what it would take to start a project for the M70. So far no reply.

Here is the Maserati https://www.ebay.com/itm/MASERATI-32...-/174065263593

My Encoders are worn on MY E31 and causing intermittent Limp Mode and i was trying to chase down anyone who has replaced them with a solid state version

[shogun]

One of my wrenching buddies had today to drive to the bi-annual roadworthy test (Shaken) here in Japan with his E32 750. Before that he made a exhaust gas test with his own exhaust gas analyzer for CO/HC and found that the result of the exhaust gas exceeding the max permitted values. In Japan this test is done at engine idle run. He found out that one throttle valve was the problem, the wiper material in the area where the the encoder whiskers are running often = in the idle/low RPM area was apparently damaged. As he had a used spare DK on stock, he installed that one, tested and found good and passed the Shaken test and got the sticker for the next 2 years.
Looks like the problem with the wiper material on the M70 DK's is getting more and more. A new throttle housing assy EML 13541736856 costs nowadays $3861.42 (MSRP) !
Looks someone has to come up soon with a solid state version like the Maserati/Volvo contactless throttle body position sensor (TPS), which is only around $100/piece from these shops. I found these
car_clusters on Ebay for the Maserati 3200 GT https://www.ebay.com/sch/car_cluster...B&rt=nc&_dmd=2
fiesta-tech United Kingdom for the Volvo V70 C70 S60 S70 S80 XC http://www.fiesta-tech.co.uk/

[dragon850]

Cleaning the throttles is just part of the issue, the bigger problem especially on early E32 750il and an indication of what's to come on all M70 and S70 powered cars at some point is the failing throttle body encoder plate.
It fails in 2 ways:
1) Encoder surface is too badly scorn by the encoder brushes, result is gradual decline in responsiveness over the years and then dead throttle and eml light.
2) Second, there are several resistors molded into the encoder plate body under the encoder plate itself, after 30+ years they fail and the resistor value either shows infinite or very high resistance, again dead throttle.
There is no solution to this problem other than buying new throttle from BMW at $4200 or finding a used throttle.
Good news, solution was developed by E31-V12throttle and is in production currently. It will be available end of the year....