M30B35 swap notes

I wanted to leave this up here as a reference for every little snag I solved during my motor swap(s).

    1. Temperature gauge sender (TBD):
      1. This is the black connector on the coolant neck, not the blue DME coolant temp sensor/CTS. This sender must match the chassis, since it provides the gauge cluster temperature readout. Here’s the problem. The early E24 sender has two incompatible connectors with the E35 harness. They’re both male spades in the early car. I believe the smaller one is the variable sender, the larger one is the switch. So I should have a dual output sender for my ’86 chassis, but the B35 harness doesn’t have those wires as far as I can tell.  – two circuits, grounded through the block. One circuit is the variable resistance output for the temperature gauge. The other circuit is a simple binary switch for an E24 exclusive…the ‘overheating’ light in the red zone of the temperature gauge.
      2. The B35 harness (’90 535i) is also grounded through the block but it only has a single gauge output. MyE28 explanation is here. At some point in time, like ’86, the gauge overheating light function was incorporated into the Check Control system. The net result is that the B35 variable output is on the wrong pin in the B35 engine harness connector. Swapping the harness pins inside the socket should solve the problem for the outputs, I might make a jumper just to leave the B35 harness unmolested. I’m also not sure the sender uses the same range as the gauges are expecting. I’ve heard a rumor than an M20B27 SuperEta or late M20B25 (Motronic 1.1/1.3) sender can alternatively be used to adapt the B35 harness to the E24 chassis without re-pinning the sender connector.
    2. Oil level sender (TBD):
      1. This sender should have three wires for my E24 chassis. MyE28 explanation is here. Two outputs (dynamic and static oil levels) and a floating ground. I’m told the static switch is closed when the float is up, dynamic is open. They flip-flop when the oil level drops. The E34 B35 motor has a different connector (square three-pin) to replace the earlier-style two-pin round type. I suspect that both these connectors are grounded externally, but some ETMs show a floating ground. I liked the E34 connector bracket, it bolts so nicely onto the driver’s motor mount arm, so I decided to keep the E34 setup if possible. IIRC the E34 has a three-pin connector but only two pins in the harness. The E24 chassis expects two signal wires, but my Euro engine harness C101 isn’t the same (of course). It doesn’t even fit into the correct pins on the NA ’86 fuse box. TBD. I moved a wire or two, but no change yet.
      2. I took a chance on moving the pin in the Euro C101, IIRC it was a brown/red wire moved from socket 11 to 4. No change.
      Dynamic Oil Level Blue/White 13 2 Dynamic oil level Blue/White
      Oil Pressure Light Brown/Green 14 23 Oil Pressure Light Brown/Green
      Service Indicator White/Blue 14 19 Goes to data link connector pin 7 White/Green
    3. CEL (TBD): R3v link here. Likely that there is a diode on the cluster leg. RMEuropean has a good writeup here, including a great M52B28 recipe. Pin 11 on the E30, described here at R3v:
    4. Pin#11 – White/Blue – Service Reset – This wire connect from C101 straight to pin 7 of the diagnostic connector from the gauge cluster. By grounding this it resets the service indicator located in the gauge cluster. This will not work correctly if your SI batteries are on their way out. In e36 engine swaps this function is maintained by connecting to x20 pin 19. For most other engine swaps you are going to have to find another way to ground out this pin conveniently. I have used the OBD port before.
        1. iv. Diagnostic plug wiring (same except needs power)
          In order to be able to check codes and communicate with the DME, we wanted to keep as much of the diagnostic plug of the S38 B38 engine wiring harness intact as possible. What we did not do, is wire in a check engine light into the dashboard, although this would be entirely possible to do with the right wire output, and the DME has this capability.In order to be able to reset the SI lights, we had to connect the C101 plugs through the X20 plug to pins 7 and 16 on the diagnostic plug. In reality, you only need pin 7, but pin 16 is needed to use the Peake reset tool.
    5. There are some other considerations for the oil sender and the A/C system. The A/C clutch is automatically disabled at WOT. Here’s some details at M535i.org, along with the information about running a connection for the SI lights to the C101 for reset computers to work properly:

v. AC wiring
As far as AC is concerned, currently I have the AC on Signal spliced into the AC wiring of the car. The AC on signal from the switch is spliced to the DME via pin 6 on X20. In the future I will have to add a relay for the compressor control. Basically the AC compressor on is going to run into pin 30 of the relay. It will also run into pin 86 and be spliced into the DME. Then pin 85 will be grounded into the DME as the full throttle switch off. And then pin 87 will run out to the clutch. These will use pins 4,5,6 on X20 to control the A/C, where pin 4 is the AC compressor on signal, pin 5 is from the A/C pressure switch, and pin 6 is the AC on signal.

  1. I did manage to wire up a CEL in the ’86. I used a spare spot in the dash, I believe it’s for traction control? Wiring is easy, just get yourself a spare gauge bulb harness. Run one leg from the grey wire in pin #12 of the C101. Run a ground wire to the other leg. Pull the bulb harness through a convenient hole in the firewall, ziptie it into the gauge harness, done!