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Documenting a Budget DIY Plug-n-Play Standalone

Old 01-05-2019, 06:39 PM
  #16  
odonnell
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Dare: regarding finding a dead DME, are you a member of any of those 944 Facebook pages? Easiest way to quickly get a part these days. If all else fails drop me a line, I have a buddy with a pile of DMEs and I'm sure he would send you one for very little.

So onto the pin assignments. This is what I have been able to figure out:




Some discussion on the above:
  • The bolded or colored text means that the thicker jumper wires should be used instead of normal 36 AWG. I ordered 28 AWG.
  • You will see there are 'options' for a MAF and for a BMW TPS sensor. I will discuss more on this later. I am using a MAF but this is not typical for most installations, MAP/speed density is fine unless you live in an area with huge elevation changes. The TPS sensor is highly recommended however, as you will get better throttle tip-in response. The stock 944 sensor is not capable of providing this information to MS so an E36 part is used instead. More info to come soon.
  • Pin 11 is the economy signal. You don't need this connected. However, I found references that it has a role in the tachometer signal in the late 944. There is also Pin 21, which is called tach signal, but this doesn't exist on my early 944 harness. I am still looking through wiring diagrams but if anyone knows which of these pins is the true source of the tach signal, please drop a line!
  • Pins 33/34 are only utilized on a late 944. The early 944 has an "auxiliary air valve" which operates independently of the ECU. Late 944 has a PWM-controlled idle valve, which MS will run. To convert the 3-pin IAC into something MS can control, one half will be pulled to ground and MS will just tell it when to open. More on this later.
  • Pin 29 told the DME when the AC compressor clutch was kicked on, and the tune was changed to keep the idle speed proper. MS has many inputs/outputs that are user-defined so we can do the same.
  • The new cam speed sensor will fill the role of the stock speed sensor. However it will need switched 12v from outside the harness. This will be discussed later. The signal from the sensor, as well as its ground, are passed through the stock harness.
Another discovery I made was the stock DME coolant temp sensor (blue connector) and the stock TPS don't ground through the DME. This is not what I had assumed as first, usually you want to give your sensors a dedicated ground back to the ECU for the best possible reading. Instead, they actually ground at the bellhousing. There are 2 ground points there from the stock wiring harness. The larger lug goes to the ground points you see in the chart I posted above, for the DME (except I had 1 pin with no continuity, not sure why). The smaller lug goes to these sensors plus potentially some other stuff. So when installing this ECU, it will be absolutely mandatory that these grounds are taken apart and cleaned until they sparkle!

For physical implementation, I have added the jumpers that don't need the thicker wire since I'm still waiting on those. I tried 2 approached. First, directly soldering the male pin to the DME connector pin. This works but I much prefer cutting off the male pin and stripping the wire to get a bare end. Then, solder this to the pin. In both cases I cleaned the DME pin with acetone (to remove any conformal coating leftover from manufacturing) and used adhesive-lined heat shrink sleeves + heat gun. First 2 pictures show the direct pin soldering, the last 2 show the preferred method.






Last edited by odonnell; 01-05-2019 at 07:34 PM.
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Old 01-05-2019, 09:58 PM
  #17  
Dare
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Michael, I think the choice of adhesive-lined shrink tubing is good, as you'll want a lot of support against vibration for those soldered connections, especially with the leads cantilevered like that. Looking at the pictures I might position the shrink tubing a little more over the wire insulation to make sure there's a good mechanical connection.

Also the solder joints look a little gloppy. Is your iron hot enough? This might be an issue for the DIYer with a low-power iron, as those connector leads will soak up a lot of heat.

Regarding the grounds, its possibly different for the early/NA cars, but on my '86 951 the TPS ground goes to Weld Point 4, which is a pressure weld located roughly in the non-ribbed part of the snorkel. From there there are separate wires to pins 5 and 28 on the DME, and the big wire to the engine block ground point (all detailed in my harness wire list spreadsheet, FYI). Your point about cleaning the engine grounds is spot on, though. Probably save people a lot of trouble down the line.
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Old 01-05-2019, 11:07 PM
  #18  
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Thanks for the feedback - I agree the solder joints don't look great. I will try increasing the temp. I initially bought this adjustable Weller station because in the past, my bad habit was to overcook solder joints. Still learning! Used to wire/wire connection and small through-hole soldering. And I will take your advice on the heatshrink position as well. I may remove all of these and start over, although mechanically they seem very strong.

Regarding the 951 TPS ground, it's a bit different as the TPS signal goes through the KLR. I'll use your spreadsheet as reference material. Thanks!
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Old 01-07-2019, 11:24 PM
  #19  
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Great Article, Michael! Good to see ya back on here! Keep up the great work!
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