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Thread: Motronic 35 Pin to 55 Pin Adapter

  1. #1
    Join Date
    Jun 2009
    Location
    Co Spgs/ Denver CO
    Posts
    753
    My Cars
    1991 325iX

    Motronic 35 Pin to 55 Pin Adapter

    Hey all,


    This idea stemmed from a discussion on mye28.com, some of you don't frequent that forum so I am posting here. I come from the e30 world and was turned on to the shortcomings of Motronic 1.0 when i bought a euro 325iX that ran Motronic 1.0 and a 073 ECU (35 pin). I started modifications and learned it did not come with all of the sensors necessary to upgrade to the later Motronic 1.3 in order to run a 55 pin ECU and/or a Megasquirt unit built into a 55 pin board.


    I ultimately performed an engine harness upgrade and supporting sensor upgrade to make my car run the 55 pin M1.3 and Megasquirt for forced induction. I was and still am surprised nobody has made an adapter for the 35 pin ECU's to the 55 pin so they could plug and play a 179 or similar ECU (megasquirt). I also learned at that time that the M20b27 (325e/s,528e) uses the 35 pin board and is the basis for the 2.7i stroker engines that is common in e30 circles. Why not have the ability to fully tune spark and fueling without having to change engine wiring harnesses or buy multiple pricey EPROM chips?


    So I decided to look into the adapter and found the correct 35 pin male connector that allows this possible and am currently waiting on the 55 pin connector to see if this will work. Assuming I found the correct adapter, the next step would be wiring the circuit up correctly and building a prototype to test. Also something to note is the db37 cable is not needed with this setup so the unit does not have unnecessary cables and should be able to fit in the factory space. Here is a simple graphic to show you how it would work.





    In case you are unfamilar with Megasquirt, here is the DIYPnP 55 pin kit that you can buy unassembled, or you can buy prebuilt running the Microsquirt module and MS2/E v3.0.3 or later.
    https://www.diyautotune.com/product/...assembled-kit/





    Some features of megasquirt if you are unfamiliar:
    Speed Density, Alpha-N and Hybrid Alpha-N (both SD and A-N algorithms hybridized) Supported
    Onboard 2.5 bar MAP sensor
    2 Ignition Inputs (for dual wheel ignitions)
    4 Spark Outputs (Up to 4 Cylinder Coil On Plug, up to 8 Cylinder Wasted Spark)
    Natively support two fuel outputs for batch or bank-to-bank fueling. Optionally upgrade to 4cyl sequential or 6/8 cyl semi-sequential with this module.
    Enhanced Acceleration Enrichment (EAE)
    Boost Control
    Knock Control
    Launch Control
    Flat Shift
    Tachometer Output
    Fully Adjustable Rev Limiter
    Table Switching
    4 General Purpose Outputs
    4 General Purpose Inputs (2 analog, 2 digital)
    Support for Flex Fuel
    Optional Realtime Baro Correction
    Closed Loop O2 Correction
    Plenty of Proto Area, add your own customizations!


    Some other suppliers of 55 pin Megqsquirt units include Sssquid Tuning (http://sssquid.com/v2/shop/tunes/bmw/megasssquirt/), Whodwho's 55 pin unit on R3vlimited.com (http://www.r3vlimited.com/board/showthread.php?t=202653), Dedericms.com (his site is down now though)


    What will you need to fit megasquirt to your e28?
    - Variable TPS off of an e34 automatic, or variable TPS from an e36 with adapter bracket (I found a supplier and maybe able to provide these also)
    *Note one wire usually needs to be swapped to make this TPS work, so I am looking into a TPS to vTPS adapter as well)
    - 60-2 toothed wheel/harmonic balancer and CPS/bracket from e34
    - Intake Air temp sensor (GM, or the sensor in the factory AFM unit)
    - Vacuum line to the ECU
    - 55 Pin ECU (Megasquirt or BMW ECU)
    - High Impedence Fuel Injectors (or i read low impedence injectors could possibly be used with certain megasquirt settings)
    - 55 pin engine Wiring Harness OR this 35 pin adapter
    - (Not necessary but a wideband oxygen sensor like the AEM UEGO or Innovate LC-1 is recommended.)


    What cars will this theoretically* work on?
    *this assumes the pinout will work and I have not yet verified all of the models listed below are 35 pin, but it should include m30b35 models through mid 1987 with the 35 pin ECU connector. This also assumes you can find a 60-2 CPS wheel/sensor which is available for the e23/e24/e28/e30. I believe you can use an m30b35 cps/wheel on the s38 and/or s38b36 cps/wheel on the s38b35 but i am not aware of an option for the s14. The m42 could possibly fit but I have not heard of anybody trying it yet.
    Code:
    325e/es
    E30
    M20/B27 (122hp)
    9/84-12/86
    0 261 200 027
    Bosch Motronic Basic M1.0
    
    
    325i/ECE
    E30
    M20/B25 (171hp)
    85-87
    0 261 200 081
    Bosch Motronic M1.0
    
    
    M3
    E30
    S14/B23 (195hp)
    86-08/89
    0 261 200 071
    Bosch Motronic M1.0 Motorsport
    
    
    M3
    E30
    S14/B23 (215hp)
    09/89-90
    0 261 200 091
    Bosch Motronic M1.0 Motorsport
    
    
    M3 - Evo2
    E30
    S14/B23 (220hp)
    88
    0 261 200 090
    Bosch Motronic M1.0 Motorsport
    
    
    M3 - Evo3
    E30
    S14/B25 (238hp)
    01/90-05/90
    0 261 200 092
    Bosch Motronic M1.0 Motorsport
    
    
    533i
    E28
    M30/B32
    84
    0 261 200 008
    Bosch Motronic M1.0 Basic
    
    
    528e
    E28
    M20/B27
    9/84-12/86
    0 261 200 027
    Bosch Motronic M1.0 Basic
    
    
    535i/is
    E28
    M30/B34
    85-87
    0 261 200 059
    Bosch Motronic M1.0 Adaptive (24 pin)
    
    
    535i/is
    E28
    M30/B34
    88
    0 261 200 059
    Bosch Motronic M1.0 Adaptive (28 pin)
    
    
    535i/is
    E28
    M30/B34 (218hp)
    85-87
    0 261 200 061
    Bosch Motronic M1.0
    
    
    M5/M635CSI
    E28/E24
    S38/B35 (260hp kat)
    87-88
    0 261 200 079
    Bosch Motronic M1.0 Motorsport
    
    
    M5/M635CSI
    E28/E24
    M88 (286hp)
    84-87
    0 261 200 055
    Bosch Motronic M1.0 Motorsport
    
    
    633csi
    E24
    M30/B32
    84
    0 261 200 008
    Bosch Motronic M1.0 Basic
    
    
    635csi
    E24
    M30/B34
    85-87
    0 261 200 059
    Bosch Motronic M1.0 Adaptive
    
    
    635csi
    E24
    M30/B35
    86-88
    0 261 200 150
    Bosch Motronic M1.1
    
    
    733i
    E23
    M30/B32
    84
    0 261 200 008
    Bosch Motronic M1.0 Basic
    
    
    735i
    E23
    M30/B35
    09/80-09/82
    0 261 200 001
    Bosch Motronic M1.0 Basic 
    
    
    735i
    E23
    M30/B34 (218hp)
    84-87
    0 261 200 011
    Bosch Motronic M1.0 Adaptive
    
    
    735i
    E23
    M30/B34
    84-87
    0 261 200 059
    Bosch Motronic M1.0 Adaptive
    
    
    745i
    E23
    M102/B34 (252hp)
    83--86>
    0 261 200 013
    Bosch Motronic M1.0

    I was able to find a 35 pin connector and received it in the mail today. Here are a few (sorry for the poor quality) pictures of the connectors I received and the test fit into my 35 pin engine harness. One shows the connector next to my 35 pin 073 ECU.

















    As mentioned above, on top of this adapter, I am considering sourcing components to create a TPS to vTPS adapter. This would be a similar male to female adapter that could plug into the factory engine harness wiring for the TPS and would allow you to run the e36 vTPS without having to rewire anything. All you would need is the variable TPS from a later BMW.


    I could do a similar adapter that would plug in to the factory AFM connector and could be wired to a GM open element IAT sensor. The benefit to all three of these adapters is that they would make everything reversible and you could install a 55 pin ECU, or 55 pin Megasquirt and if you decided you wanted to sell the car without it, or return the vehicle to stock for one reason or another, you could return it back to the factory electronics very easily.


    With that said, I would like to gauge interest in this adapter circuit. Who would be interested in one, and if we have enough interest and this first prototype works as expected, maybe we can start a list for a preorder.

    1991 325iX

  2. #2
    Join Date
    Feb 2015
    Location
    Maryland
    Posts
    1,221
    My Cars
    325ix, 325ix, 540i
    Best of luck. That is a really large under taking.
    If your e30 runs bad, switch to Megasquirt first. Then try new spark plugs, cap and rotor, wires, oxygen sensor, crank shaft position sensor, coolant temp sensor, air flow meter, idle control valve, throttle position sensor, digital motor electronics unit, harmonic balancer, fuel injectors, engine harness...

  3. #3
    Join Date
    Jun 2009
    Location
    Co Spgs/ Denver CO
    Posts
    753
    My Cars
    1991 325iX
    Great news. The connectors and pins pins came today so I was able to test fit the components together. The 55 female connector fits properly in the ecu housing and it comes with the locking metal bracket to secure it to the ECU. The female terminal pins seem to fit and slide properly over the male pins of the ECU. They appear to fit but i didn't click a pin into place because I am not sure I could remove it. The next step would be to verify the wiring pinouts and double check whether I need shielded cable for components such as the CPS. I will probably wire this first one up for the 55 pin DIY PNP unit and not the db37 connector.

    Anyway, here are some photos of how it is coming together! Note the metal bracket that slides into the housing and the plastic 'hook' on the opposite side that secures it to the ecu very solid.











    And here is a quick preview of how it should go together. I don't have heat shirnk for the wires yet and probably won't on this prototype model. I may order some 3 pin connectors to assemble a TPS to vTPS adapter too.


    1991 325iX

  4. #4
    Join Date
    Jun 2009
    Location
    Co Spgs/ Denver CO
    Posts
    753
    My Cars
    1991 325iX
    Time for a weekly update. The first step to making the 35 pin adapter work is ensuring you've got a variable Throttle Position Sensor (from an e36) so the MS unit can interpret the signal vs the original switch style sensor that comes with the cars of the era. I found the bosch 3-wire connector that plugs into the wiring harness and thought i had ordered all necessary parts to make my first TPS to vTPS. When they arrived, it turns out i had 2 female adapters instead of one male and one female. I got the wire seals, terminals, and even found the rubber boot to cover the wires. Unfortunately, after some research and contact with the manufacturer, the male version is not available due to some contract with the manufacturer. There is a drawing from the manufacturer for reference only so you can manufacture your own male connector. :shock:





    Here are the 2 connectors I received, probably going to go with the longer run due to pricing differences.





    I was able to sleauth my way into a 3 prong male connector and ordered some of those to make sure I have the right male connector to finish the adapter. Here is an example of how it will look. I am working on putting together a TPS to vTPS adapter kit that would include the wiring adapter, the vTPS sensor, and a bracket to mount the vTPS to the m20/m30 throttle body. I anticipate that kit to be ~$100 shipped, or half of that if you sourced your own vTPS.


    Here are a couple pictures of half of the TPS adapter harness... waiting on the male connector at the moment. The rubber dust cover costs almost $3 per unit and each adapter would have 2, so I may try heat shrink to keep costs down. The rubber wire seals should keep dust and debris out of the connector so I don't think the rubber cover is absolutely necessary. Any thoughts or preferences?


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    1991 325iX

  5. #5
    Join Date
    Jun 2009
    Location
    Co Spgs/ Denver CO
    Posts
    753
    My Cars
    1991 325iX
    I build my first prototype tps adapter and it worked. Here area couple of pictures. I didn't use heat shrink or the rubber dust boots on this one in case I had a problem. Here are a few pictures as well as once I installed it on my car and tested it. Note I am using a homemade adapter bracket not the one that will come in this kit.




















    I did a datalog, but ignore the AFR readings as i am running the engine on basically stock Motronic 1.3 with a narrowband oxygen sensor.

    1991 325iX

  6. #6
    Join Date
    Nov 2018
    Location
    France
    Posts
    1
    My Cars
    325ix

    Additional data

    Hi 02rollin,
    I'm on the way to do the same adapter as the one you did.
    Could you please post the pinout wiring correspondence between the 35 to 55 pins you did ?
    Thanks in advance

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