Using DIYAutoTune.com’s Nissan Optical Trigger Discs

Converting your Nissan distributor to a more MegaSquirt friendly design

Updated 12/18/2014

Many Nissans used a distributor or CAS with a set of four or six inner slits and 360 outer slits. Current MS3 firmware supports the SR20DET, RB series, and VG30DE/DETT trigger wheels, but MS1 and MS2 are only able to use this type of trigger wheel for a basic distributor. To get around this limitation, we’ve come up with a set of bolt in trigger wheels for many Nissan applications, including the L28ET, VG30E / VG30ET, KA24E / KA24DE, and SR20DE / SR20DET.

These motors use a fairly easily replaced trigger wheel. You just need to remove the distributor cap and rotor, or the CAS cover. There’s a single Philips head screw that holds the trigger disc and its mounting plate in place. Just unscrew this, remove the disc and put ours in its place, and bolt it back together. Our trigger discs are meant to be installed in the orientation shown below; if they are installed upside down, you’ll need to change the trigger angles and some other settings.

tw-sr20TW_L28ET

Note that some motors may use different angles from the ones shown in this writeup, as we haven’t been able to test the trigger wheels in-house on all possible applications. If you find one of the engines needs trigger angles that are off significantly, please contact us and we’ll add the information to this article. Because the CAS or distributor has some built in adjustment, it’s likely that many installs may need as much as 20 degrees of adjustment, so you will need to check your timing with a timing light. Treat these values as a starting point, not the definitive, final numbers.

The RB motors, VG30DE / VG30DETT, and CA18DET use a different cam angle sensor that is difficult to take apart. DIYAutoTune.com currently does not make a bolt in disc for those, although we could add this if demand is there. The current MS3 code supports these stock trigger wheels on these motors, without swapping out a trigger wheel.

ECU Modifications

We have articles that cover the input side and wheel decoding. There are several possible ways you can set up the output side, including using BIP373 internal ignition modules, the QuadSpark external ignition module, or an MS3 with MS3X outputs running LS1 coils or our IGN-1A directly.

Also note that MS2 and MS3 can use this to get more resolution over the standard trigger wheel when running as a distributor.

Using the MS-I V3.0 or V3.57 with MS1/Extra

Wasted spark ignition

Hardware mods – V3.0

  • This is assuming you are starting with an ECU built up like I build my assembled MS130-C MegaSquirt-I PCB3.0 units.  If you are building your unit up from a kit you can implement these changes during assembly.
  • Make sure it is set for Hall / optical input (TachSelect to OptoIn, TSEL to OptoOut).
  • Flash ECU with MSnS-E version 029v or later.   
  • Cut out C12 and C30.  (Only needed when triggering from the – terminal of the coil, which you are not)
  • Remove D1 and jumper it, or just install a jumper wire across it’s leads.  (Only needed when triggering from the – terminal of the coil, which you are not)
  • Cut out R57 if fitted (this won’t be there on my units though).
  • Connect S12 to TachSelect using a 1K resistor. (Or you can use a 1K pull up in the wiring, between pin 24 and a 12V source.)
  • Install the spark output of your choice. BIP373 or QuadSpark output mods are two possible choices. You can use the “5V pull up” mods if using a stock SR20DET ignition module.

Hardware mods – V3.57

  • For a V3.57, you’d have to remove a lot of parts to use the Hall / optical input, so we’ll just bring this in through the VR conditioner instead.
  • Place the JP1 jumper in the 1-2 position.
  • Place the J1 jumper in the 5-6 position.
  • Put a 1K resistor in the R57 slot (Or you can use a 1K pull up in the wiring, as above.).
  • Install the spark output of your choice. BIP373 or QuadSpark output mods are two possible choices. OEM Nissan SR20DET ignition modules can use 5 volt logic level outputs – this link covers the V3.0, but the V3.57 uses the same schematics.

TunerStudio settings

  • Under Codebase and Output Functions, set Wheel Decoder to Generic Wheel, all other outputs off.
  • Set LED17 (D14) function to Spark Output A.
  • Set LED19 (D16) function to Spark Output B.
  • On 6 cylinder applications, set LED18 (D15) function to Spark Output C.
  • Do not turn on any further spark outputs.
  • Trigger angle: 75  (This varies slightly between individual engines. Check with a timing light and adjust as needed.)
  • Four cylinder wheel decoder settings:
    • Wheel decoder base teeth: 12
    • 2nd trigger enable: Off
    • Missing teeth: -1
    • Trig pos A: 10
    • Trig pos B: 4
    • Set all other positions to zero.
  • Six cylinder wheel decoder settings:
    • Wheel decoder base teeth: 12
    • 2nd trigger enable: Off
    • Missing teeth: -1
    • Trig pos A: 10
    • Trig pos B: 2
    • Trig pos C: 6
    • Set all other positions to zero.
  • Spark Output Inverted will depend on your output mods. BIP373s and the QuadSpark both require setting Spark Output Inverted to Yes. Getting this setting wrong can damage the ignition module and/or coils. If the ignition module or coils get hot with the key on and the engine off, turn the key off immediately and select the opposite output setting.

Using the MS-II V3.0 or V3.57 ECU with MS2/Extra

  • Make sure it is set for Hall / optical input (TachSelect to OptoIn, TSEL to OptoOut).
  • Cut out C12 and C30.  (Only needed when triggering from the – terminal of the coil, which you are not)
  • Remove D1 and jumper it, or just install a jumper wire across it’s leads.  (Only needed when triggering from the – terminal of the coil, which you are not)
  • Cut out R57 if fitted (this won’t be there on my units though).
  • Connect S12 to TachSelect using a 1K resistor. (Or you can use a 1K pull up in the wiring, between pin 24 and a 12V source.)
  • If you want sequential coil on plug (or sequential injection with the 3.2.1 code), you’ll also need a second trigger input. Solder a 1K resistor onto a length of wire, and cover the resistor with heat shrink tubing. Connect this resistor-on-a-wire combination from JS10 to SPR1.
  • Solder a 470 ohm resistor onto a length of wire and cover with heat shrink tubing. Run this resistor-on-a-wire from the 5 volt terminal in the proto area to SPR1.
  • Connect a 0.1 uF capacitor from JS10 to SG or the proto area ground.
  • Install the spark output of your choice. BIP373 or QuadSpark output mods are two possible choices. OEM Nissan SR20DET ignition modules require 5 volt logic level ignition outputs.

Hardware mods – V3.57

  • For a V3.57, you’d have to remove a lot of parts to use the Hall / optical input, so we’ll just bring this in through the VR conditioner instead.
  • Place the JP1 jumper in the 1-2 position.
  • Place the J1 jumper in the 5-6 position.
  • Put a 1K resistor in the R57 slot (Or you can use a 1K pull up in the wiring, as above.).
  • If you want sequential coil on plug (or sequential injection with the 3.2.1 code), you’ll also need a second trigger input. Solder a 1K resistor onto a length of wire, and cover the resistor with heat shrink tubing. Connect this resistor-on-a-wire combination from JS10 to SPR1. You could also use PAD7 if you’d rather bring the input in through the DB15.
  • Solder a 470 ohm resistor onto a length of wire and cover with heat shrink tubing. Run this resistor-on-a-wire from the 5 volt terminal in the proto area to SPR1 (or PAD7 if you used this in the preceeding step.).
  • Connect a 0.1 uF capacitor from JS10 to SG or the proto area ground.
  • Install the spark output of your choice. BIP373 or QuadSpark output mods are two possible choices. OEM Nissan SR20DET ignition modules require 5 volt logic level ignition outputs.

TunerStudio settings (Batch fire / wated spark or single coil)

  • Settings under Basic Setup -> Tach Input / Ignition Settings:
    • Spark mode: Toothed Wheel
    • Ignition input capture: Falling Edge
    • Spark output will depend on what output setup you’re using. BIP373s and QuadSparks both use Going High / Inverted.Getting this setting wrong can damage the ignition module and/or coils. If the ignition module or coils get hot with the key on and the engine off, turn the key off immediately and select the opposite output setting.
  • Settings under Basic Setup -> Trigger Wheel Settings:
    • Trigger wheel arrangement: Single wheel with missing tooth
    • Trigger wheel teeth: 12
    • Missing Teeth: 1
    • Tooth #1 angle: 345 (This varies slightly between individual engines. Check with a timing light and adjust as needed.)
    • Wheel speed: Crank wheel

TunerStudio settings (Sequential coil on plug and / or sequential fuel)

  • Settings under Basic Setup -> Tach Input / Ignition Settings:
    • Spark mode: Toothed Wheel
    • Ignition input capture: Falling Edge
    • Spark output will depend on what output setup you’re using. BIP373s and QuadSparks both use Going High / Inverted.Getting this setting wrong can damage the ignition module and/or coils. If the ignition module or coils get hot with the key on and the engine off, turn the key off immediately and select the opposite output setting.
  • Settings under Basic Setup -> Tach Input / Ignition Settings:
    • Trigger wheel arrangement: Dual wheel with missing tooth
    • Trigger wheel teeth: 12
    • Missing Teeth: 1
    • Tooth #1 angle: 345 (This varies slightly between individual engines. Check with a timing light and adjust as needed.)
    • Wheel speed: Crank wheel
    • Second trigger active on: Rising edge


Using the MS-III V3.0 or V3.57
ECU with MS3X for full sequential

  • The MS3 manual generally favors the VR input, so we’ll be using that.
  • Place the JP1 jumper in the 1-2 position for a V3.57. For a V3.0, jumper TachSelect to VRIN.
  • Place the J1 jumper in the 3-4 position for a V3.57. For a V3.0, jumper TSEL to VROUT.
  • Put a 1K resistor in the R57 slot on a V3.57. For a V3.0, run a 1K resistor from S12 to TachSelect. (Or you can use a 1K pull up in the wiring from a 12 volt source to pin 24 of the main board.)
  • The second trigger input also needs a pull-up. Install JP7.

TunerStudio settings (Sequential coil on plug and / or sequential fuel): All are under Ignition Settings -> Ignition Options / Wheel Decoder.

  • Spark mode: Toothed Wheel
  • Ignition input capture: Rising Edge
  • Spark output will depend on what output setup you’re using. QuadSparks use Going High / Inverted; so do OEM SR20DET ignition modules. Getting this setting wrong can damage the ignition module and/or coils. If the ignition module or coils get hot with the key on and the engine off, turn the key off immediately and select the opposite output setting.
  • Trigger wheel arrangement: Dual wheel with missing tooth
  • Trigger wheel teeth: 12
  • Missing Teeth: 1
  • Tooth #1 angle: 345 (This varies slightly between individual engines. Check with a timing light and adjust as needed.)
  • Wheel speed: Crank wheel
  • Second trigger active on: Poll Level

Wiring notes

Nissan used several different wire setups over the years. Here are several known examples. The primary trigger always wires to pin 24 on the main board DB37. For MS2, the second trigger wires to pin 3 on the main board DB37, or pin 7 on the DB15 if using the optional V3.57 DB15 input. For MS3, the second trigger wires to MS3X pin 32.

Distributor Wire Colors: 280ZX and Z31 300ZX

Colors of the wires on the distributor side of the 4 pin round connector, versus on the harness side.  You can connect in from either side. Colors shown are for factory wiring harnesses

Distributor SideHarness SidePurpose
RedB/W12v+
WhiteG/BPrimary (Crank) Trigger
GreenG/YSecond (Cam) Trigger
BlackBlackGround

 

Distributor Wire Colors: 240SX

’89-’90’91 and laterPurpose
B/WB/W12v+
G/BWhitePrimary (Crank) Trigger
G/YBlackSecond (Crank) Trigger
BlackBlackGround