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2000 E46 323i, 3.0L, 2.8L and 2.0L Z3's
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I've had a good look at the test results.

The design of the MDK is interesting.
  • There are 2 sets of Potentiometers. This allows the DME to compare one with the other to create a fail-safe system.
  • Within each set, one potentiometer is biased the opposite to the other. This allows for mathematical checks within the potentiometer set. More fail-safe features.
  • All connections within the potentiometer sets are available to the DME. This allows for mathematical checks between the potentiometer set. Yet more fail-safe features.
  • The potentiometers within a set are connected in parallel. From the test results we can conclude that the individual potentiometers have the same resistance, that is twice the resistance of the paralleled pair, so that is 2,000 ohms.
  • The test results show that the minimum resistance on each potentiometer is 1,000 ohms.
  • This makes sense. Engineers like using easy numbers, so a 2,000 ohm Potentiometer with a 1,000 ohm minimum reading, gives a 1,000 ohm range for 100% travel, or 10 ohms per every 1% of travel.
  • The potentiometer supply is 5V. This means that the maximum current draw is 5/1,000 = 5mA and the minimum current draw is 5/2,000 = 2.5mA on any leg of the system.
  • We test for resistance but the DME measures Voltage.
What we do not know, is what mathematical checks the DME does to ensure that the MDK is safe to use. There are a lot of options with the layers of fail safe in the design.

We do know that the MDK has problems with poor electrical connections. The added resistance upsetting the checks and balances (fail-safe) that the DME does.

If you look at it from a resistance perspective, you get these results. This shows that your MDK is out of spec.
Font Material property Parallel Screenshot Rectangle


Remember that this is a test sample of 1 and we are trying to do something new and different. We could be doing this all wrong.
 

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I've tested my 2nd TB:

2 - 4 : 1048
1 - 7 : 1041

2-5 1834 - 1154
2-3 1952 - 1173
1-6 1965 - 1191
1-8 1812 - 1124

4-3 1228 - 1958
4-5 1165* - 1831
7-6 1229 - 1968
7-8 1163 - 1821

*4&5 pins are very sensitive, on different TB (as a whole) positions the starting value was changing in the 50 Ohm range.
Re-tested the 1st TB, got different values for 4&5: 1237 - 1865 instead of old 1040 - 1725.
Could've been my error during the first measurements. The values were not changing like in the case of the 2nd TB when I was moving around the TB.

Generously applied wire cleaner by ABRO. Interesting to see if values will change tomorrow.
 

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2000 E46 323i, 3.0L, 2.8L and 2.0L Z3's
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Here is the updated Resistance table for the first MDK
Font Rectangle Material property Pattern Parallel


Here are the test results from the second MDK
Font Rectangle Material property Pattern Screenshot

  • All of the high resistances are within tolerance.
  • All of the low resistances are not in tolerance.
  • You have noted 50 ohm resistance jumps/changes between pins 4 and 5 with the MDK closed. This is a sign of a faulty MDK.
The M52TUBXX engine runs on the Idle control valve for lots of the low rev's operation. My testing has shown that for steady speed operation, the Throttle body does not start opening until about 50kph (30 mph). The throttle body does open during acceleration around those speeds, but the results are related to steady speed conditions. At a steady speed of 100 kph (60 mph), the throttle body is only open 12%. This means that the throttle body spends most of its time operating in the 0% to 30% opening range. This is the area of most wear on the carbon resistance strip and probably why you have detected damage on the second MDK at the start/closed position for pins 4 and 5.

I've been doing some more work on testing the MDK. It's not finished. Looks like I'm going to have to pull a known working MDK and do some testing to confirm my thinking.
 

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2000 E46 323i, 3.0L, 2.8L and 2.0L Z3's
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Had some time to test my cars with the Foxwell NT530 scanner with BMW software. Interesting results. Got all this data from the scanner. Still working my way through it, but thought that you may like to see it in in the raw.

Car was stationary during the tests, key in position 2 with the engine off.

Font Material property Parallel Number Pattern
 

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I've just remembered that during resistance measurements when I was rotating the axe (which is connected with the cable) the values were always changing BUT when I was rotating the smaller metallic part (the one that overrides cable-axe position) on some pins the values were not changing. Is this a sign of a problem?
 

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The metal arm that over-rides the cable cam is connected to the throttle valve/butterfly side. You were putting forces on the spring coupling between the butterfly and the cable cam in reverse. There will be some slop in the system, so by turning the system with reverse forces, the potentiometers will be turning slightly differently.
 

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If you are having jumping resistance with the MDK closed try this.

  • Fit the MDK to the car. Start it up and let the engine warm up to its normal operating temperature.
  • Reach in and adjust the accelerator cable adjuster. Turn it counter clockwise until the RPM just starts to rise. Then turn it back a bit, so the idle is at its normal level (circa 700 rpm).
  • Clear the trouble code and go for a drive. See if that fixed the problem. Let me know how it works out.
 

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I have bought used wiring harness, cut the 10 wires leading to 10-pin connector and am about to re-solder that into my existing harness. Similar to the @Effduration's 4th suggestion. Was practicing soldering during these few days... Any tips before I ruin the harness is appreciated.

My cable is loose, there's no tension at all when gas pedal is in default state, the adjustment part is not functioning. Can this be a cause of the problem?
I'm going to use the MDK that's not having resistance jumping.
 

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The idea of adjusting the cable is to try and lift the potentiometer wipes just a little away from the damaged area that causes the resistance jumping.

That's a good idea to practice our soldering skills before attempting the harness. I'm sure there are you-tube clicks that will give you all the soldering tricks and tips.

There should be a rubber grommet on the "F" mount that the cable adjuster goes through. There was one case, where it was claimed that the lack of the grommet was the cause of the problem due to too much slack. Does your cable adjuster press into a rubber grommet on the "F" mount? The part number for the grommet is 35411164739.
 

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Another question related to soldering is where to cut existing wires from?
Compared to the used wires I have bought existing ones' colors are faded. I am not sure what to make of those faded colors (caused by heat, short? or just dirt...). Cutting from deeper position will make soldering more challenging.
 

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Here are a couple of phots of how the cable should look. It looks like your cable has been replaced at some stage with one from a different car.

Have you tested the resistance of the wires in the harness? I suggest that you do, before you go the effort to change the plug.
  • Locate the connector X60003 at the DME. It's the big 52 pin connector, number 3 counting from the fire wall to the bumper.
  • Remove the outer black plastic cover, 2 tabs and the end.
  • Back-probe next to the wires to get a connection. A metal paper click works. Do not front probe the connectors. You are likely to push the probe into the small connector and damage the connector. This just make another hard to find fault to locate.
  • Attached is a PDF with a form that I use for another part of MDK testing. It gives the DME and MDK pin outs.
  • If your digital multi-meter has a "REL" button. When on ohms, hold the probes together, when the screen say zero or near zero, push the REL button. This will give you a reading relative to zero. It makes the meter more accurate.
  • Let me know what the harness resistance are. My thinking is that anything < 0.5 ohm is good.

Automotive tire Motor vehicle Automotive design Automotive fuel system Rim
Motor vehicle Automotive tire Hood Automotive fuel system Automotive design
 

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I have bought used wiring harness, cut the 10 wires leading to 10-pin connector and am about to re-solder that into my existing harness. Similar to the @Effduration's 4th suggestion. Was practicing soldering during these few days... Any tips before I ruin the harness is appreciated.
I am about to go thru this myself. I have a complete spare harness for my '99 E39 528i with M52tu. Rather than cut and solder, I think I am going to replace the entire harness with the used one I bought. I will put "Stabilant 22" or DeOxit on all the connections of the 10-pin connector for the MDK (throttle body).

This is more work, but I would rather not cut two harnesses if I don't have to... I don't mind having to replace the harness because I need to do the cooling pipes under the intake manifold anyway, and with the intake off, replacing the harness is pretty easy.

If this doesn't work, I will cut and solder the connector on my original harness per:
 

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I am about to go thru this myself. I have a complete spare harness for my '99 E39 528i with M52tu. Rather than cut and solder, I think I am going to replace the entire harness with the used one I bought. I will put "Stabilant 22" or DeOxit on all the connections of the 10-pin connector for the MDK (throttle body).
I'm on the fence regarding the need to change the harness for MDK repairs. You can test the continuity to the harness wires. Test the MDK connector through comparison of the MDK potentiometer resistances both off the car and on the car when tested at the DME. The one area you can't easily test is the DME connections. So just replace the 10 connector pins. Plus, there is already around a 800 ohm resistor in the circuit/series between the potentiometer wipe and the MDK connector. A 2 or even a 10 ohm high resistance joint in series is not going to make very much difference. Rather than highjack this thread, maybe we should discuss this in a separate thread or private conversation?
 

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Fair enough...I wasn't intending to hijack the thread..although I think any discussion of testing the MDK would be less than complete without a mention of the 10-pin MDK connector which seems to be a common source of problems...at least as common as a failed MDK.
 
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