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How to MegaSquirt your Chevy LT1, LT4 or L99 with Optispark Ignition

Getting MegaSquirt to work with the Optispark

Updated 7/3/2012 - Added MS3!

Thanks to "Mobythevan" for his notes on the settings!

Application(s): All Chevrolet LT1, LT4, and L99 engines with the Optispark distributor. This includes Camaro, Trans Am, Corvette, and B-body (Caprice, Roadmaster, Fleetwood) applications.

Level of control:  Full Standalone EMS-- Fuel and Ignition Control

 

When GM went looking for a new ignition design for the LT1, they went with a somewhat unlikely source - Mitsubishi. They bought an optical distributor system that was already in use in many Mitsubishi, Chrysler, Subaru, and Nissan applications. The stock ECU uses the 360 slot ring to determine crank angle and the inner ring of eight slots to identify the cylinders.  If you're using MegaSquirt-II, the ECU does not need or use the information provided by the second ring of 360 slits or the length of the inner slits, so you just need to obtain a signal from the trailing edge of the ring of 8 slits.   This writeup covers using a BIP373 Ignition Driver for controlling the coil.

MegaSquirt-III has a new, dedicated Optispark mode. This uses both wheels.

If you would prefer not to use the Optispark, check out our page on crank triggered ignitions. This can be used for either a distributorless ignition or using the Opti strictly as a distributor.

ECU Modifications

You can run this engine on MegaSquirt-III or MegaSquirt-II depending on your needs. It's stepper IAC motor control can drive the stock idle air control valve, which is one feature MegaSquirt-I does not have. For those looking to build this on a budget and who want to figure out another route to control your idle speed, we also have a write-up covering MegaSquirt-I.

Using the MS-III PCBv3.0 or V3.57 ECU with MS3X

  • In step 22, install the stepper IAC jumpers (all of our assembled MS3 units are by default configured this way).
  • Build the ECU up to trigger for inverted VR output. On a V3.0, wire TachSelect to VRIN and TSEL to VROUTINV. On a V3.57, put main board JP1 in the 1-2 position and J1 in the 5-6 position.

That's it!

Using the MS-II PCBv3.0 or V3.57 ECU

  • In step 22, install the stepper IAC jumpers (all of our assembled MS230-C and MS2357-C units are by default configured this way).
  • Build the ECU up to trigger from the Hall/Optical Input (all of our MS230-C and MS2357-C units are by default configured this way, too.).
  • We will need a 12 volt pull up on the ignition input. Solder a 1K resistor between S12 and TachSelect (for a V3.0 board) or pin 3 of the JP1 jumper (for a V3.57 board). It's best to wrap this resistor in heat shrink tubing and put it on the underside of the board.
  • The only change to the output side is to enable the IGBT High Current Ignition Coil Driver Circuit to directly drive the coil.  (If you're buying an assembled unit, we'll gladly do this for you for just a few bucks, shoot us an email)
    • Remove the jumper from JS10 to IGN (on a V3.0 board) or from JS10 to the center hole of Q16 (V3.57).  Some MegaSquirt ECUs may not have this jumper installed if they were not originally setup for ignition control.
    • Jumper IGBTIN to JS10
    • Jumper IGBTOUT to IGN (on a V3.0 board)
    • If Q16 is not fitted, install a BIP373 Ignition driver in the Q16 slot using a mica insulator.

(This will enable the BIP373 Ignition Coil Driver)

That's it!

 

Using the MS-I PCBv3 with MSnS-E firmware

Note the separate instructions for v3.0 and v3.57 PCBs

This will let you control fuel and ignition, but not the IAC valve.

MegaSquirt-I PCBv3.0 Mods Required: 

  • 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.
  • Flash ECU with MS1/Extra version 029v or later.
  • Install the Hall / optical input circuit (step 50A)
  • We will need a 12 volt pull up on the ignition input. Solder a 1K resistor between S12 and TachSelect. Wrapping the resistor in heat shrink tubing will protect it from accidental shorts.
  • Jumper IGBTOUT to IGN to send to IGBT ignition coil driver signal out of pin 36 on the DB37.
  • 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).
  • Get a 330 ohm 1/4w resistor and cut the leads down to about 1/2" at each end. Maybe a bit less.
  • Tin each end of the resistor with a bit of solder.
  • Cut a 5" piece of hookup wire (22ga is fine) and strip just a 1/8" or so. Tin the stripped wire with solder.
  • Melt the tinned wire tip to one end of the tinned 330 ohm resistor tip and let it cool.

  msnse_led17-d14_thru_vb921005.jpg (67542 bytes)

  • Heatshrink wrap this wire/resistor assembly.

msnse_led17-d14_thru_vb921007.jpg (79951 bytes)

  • Use this wire/resistor combo to jumper the 'top' (top as in when you facing the silkscreen side of the PCB, with the text so that you can read it normally) lead of R26 to IGBTIN on the opposite side of the PCB.

msnse_led17-d14_thru_vb921011.jpg (149401 bytes)

 

 

MegaSquirt-I PCBv3.57 Mods Required:  \

  • We will need a 12 volt pull up on the ignition input. Solder a 1K resistor between S12 and pin 3 of the JP1 jumper (for a V3.57 board). It's best to wrap this resistor in heat shrink tubing and put it on the underside of the board.
  • Get a 330 ohm 1/4w resistor and cut the leads down to about 1/2" at each end. Maybe a bit less.
  • Tin each end of the resistor with a bit of solder.
  • Cut a 5" piece of hookup wire (22ga is fine) and strip just a 1/8" or so. Tin the stripped wire with solder.
  • Melt the tinned wire tip to one end of the tinned 330 ohm resistor tip and let it cool.

  msnse_led17-d14_thru_vb921005.jpg (67542 bytes)

  • Heatshrink wrap this wire/resistor assembly.

msnse_led17-d14_thru_vb921007.jpg (79951 bytes)

  • Run this resistor on a wire combination from the right side of R26 (I know, it's kind of tricky to solder to a surface mount resistor if you haven't done much of this type of work) or pin 7 of the Ul socket (which is a lot easier to solder to) over to IGBTIN.
  • Install a BIP373 transistor in the Q16 slot, using a mica insulator.

That's it!

 

Wiring - MS3

Usually, the MS3 uses pin 32 for the cam input signal. Because of the high frequency of the Optispark, you'll be using PT4 (pin 31) instead.

Optispark pin out

Pin Purpose
A Low Resolution Signal (MS Pin 24)
B High Resolution Signal (MS3X pin 31)
C 12 volt power
D Ground

You will also need to connect 330 ohm, 1/4 watt resistors from TPS VREF (pin 26) to both the low resolution signal and the high resolution signal to provide a pull-up in the wiring harness. Wire spark output A (MS3X pin 14) to the stock ignition module. Alternatively, MS3 allows you to use the Optispark to trigger a distributorless ignition.

For the injector outputs, use the following pins.

MS3X pin Injector letter Cylinder
19 A 1
16 B 8
13 C 4
10 D 3
7 E 6
4 F 5
1 G 7
20 H 2

Wiring - MS2 or MS1

The output is quite straightforward - you will just need to connect the negative terminal of the coil to pin 36. The positive terminal of the coil you can just leave wired to it's stock location. For the ignition input side (tach signal into the ECU), wire the low resolution input signal from the Optispark pin A (this is usually either black with a red stripe, or red with a black stripe) to the MegaSquirt pin 24.

Optispark pin out

Pin Purpose
A Low Resolution Signal (MS Pin 24)
B High Resolution Signal (Not used with MS2 or MS1)
C 12 volt power
D Ground

 

 

Idle Air Control

LT1s used a stepper idle air control motor. If you have a MegaSquirt-II, you can drive it from the MegaSquirt pins 25, 27, 29, and 31. GM used several different idle air control valves on the LT1 series; they don't all have the same connector design. This picture from the MegaManual shows which wire goes where on GM idle air control motors. 

Other Things the ECU Controls

The stock ECU controls a couple other devices in these cars besides the injectors, ignition, and IAC valve. Here's what to do about the ones you will need to control.

Fuel pump: This is a standard output on the Megasquirt. Wire the Megasquirt pin 37 to the fuel pump relay wire that went to the stock ECU.

Cooling fans: These cars generally had two cooling fan control outputs. MS3 can use any of its medium current outputs on the MS3X for fan control. If you're not using MS3, use one MK-RelayCtrl mod kit for each of them if you want to control the fans. If you have an MS2, you can use the on/off IAC output on pin 30 for one of the fan controls, and use just one relay control mod kit for the other fan output. We recommend using PA0 - Knock Enable for the output, wiring the input of the transistor to pin JS11, and using SPR3 to bring the output out to pin 3 of the DB37 cable. See here for a picture of an installed relay control mod kit.

Vehicle speed output: Some Corvettes use this for features like active suspension control, and it is linked to the cruise control. MS3 has a vehicle speed output option you can use. If you're not using MS3, the easiest way to keep this active, if you want to use these features, would be to leave the stock ECU in place, just disconnected from what you have the Megasquirt controlling.

Air conditioning: MS3X can use a spare digital input and a spare medium current output to run the A/C and provide an idle up. While the stock ECU controls the air conditioner, you don't need a computer to make this work. Wiring the A/C request wire running to the ECU to the A/C compressor relay should make this work, although we have not tested this one for ourselves.

Automatic transmission: The Megasquirt itself does not control the 4L60E, but the GPIO board has this capability. You will also need a MegaShift mod kit. Otherwise, if you have an automatic you will need to either control it with the stock GM ECU or a stand alone transmission controller.

If you're doing a parallel installation to keep the stock ECU in control of the transmission, see this article for tips on parallel installs.

TunerStudio Configuration for MS-III

Under the ignition setup menu, set the following.

  • Spark mode: Optispark
  • Trigger Angle / Offset: 0 (adjust as needed if your timing doesn't line up)
  • Ignition input capture: Rising edge
  • Spark output: Going High / Inverted if using stock ignition module
  • Number of coils: Single coil
  • Spark hardware in use: MS3X spark
  • Cam input: MS3X

TunerStudio Configuration for MS-II

Set ignition capture to "Falling Edge," and coil charging to Standard Coil Charging. Dwell will depend on exactly which coil you are using. Cranking trigger time must be set to Calculated. If using MS2/Extra, set the ignition type to Basic Trigger. Trigger angle is in the 90 degree range; this may vary depending on production tolerances, so confirm this with a timing light.

Important when using the BIP373:  On the 'Ignition Settings' menu make sure to set 'Spark Output' to 'Going High (Inverted)' and set 'Coil Charging Scheme' to 'Standard Coil Charge'.

If you use someone else's .msq file we do recommend you check the firmware version the .msq file was built on as you cannot always use a file built on one firmware version with an ECU running a different version-- it's best to use the .msq files with the same version of the firmware that the file was built on.  Alternately you can manually copy the settings over from the borrowed file.

 

TunerStudio Configuration for MS1/Extra

On the 'Spark' menu choose 'Spark Settings' and set 'Spark Output Inverted' to YES.  It is critical to get the Spark Output Inverted setting correct, as setting this wrong can result in damage to the BIP373 or coil. For Trigger Angle, start with 68 degrees with a Trigger Angle Addition setting of 22.5 degrees. This may vary a little depending on production tolerances, so check this with a timing light. Dwell settings will depend on the coil used.  A typical rule of thumb is to back off the dwell until you can just barely detect a misfire under lean cruising conditions, then add 0.2 ms of dwell time.

If you use someone else's .msq file we do recommend you check the firmware version the .msq file was built on as you cannot always use a file built on one firmware version with an ECU running a different version-- it's best to use the .msq files with the same version of the firmware that the file was built on.  Alternately you can manually copy the settings over from the borrowed file.

 

 

Suggested parts

As stated above, we recommend a MegaSquirt-II V3.0 or V3.57 to have full control over the engine. You will be able to use your existing sensors except for the MAP sensor which is built into the MegaSquirt.

ECU options:

Mod kits discussed in this article:

  • MK-BIP373 if you are using a V3.57 board
  • MK-RelayCtrl will give you a relay control output. You'll need two of them for the cooling fans.
  • MK-Pullup will provide the pullup resistor needed for the internal mods described above

Other recommended parts

 

 

 

Making Your Order Easy

We've taken the above list of suggestions a step further, and used it to create two single part#'s you can order by to get everything you need, either in kit or assemble form.  So all you need to answer is, are you a hardcore DIY Build-It-Yourself from a kit kind of guy?  Or would you like it to arrive prebuilt, with all hardware mods completed, and ready to wire up with all the accessories you'll need?  (we'll even toss in a free t-shirt)

 

 

Note we left a Wideband O2 System OUT of these packages to keep your initial cost down, but as with any engine management system you'll definitely appreciate a wideband system during tuning.  We highly recommend the Innovate LC-1 with or without a gauge. 

Innovate LC-1 Wideband with DB Gauge Blue  Innovate LC-1 Wideband with DB Gauge Red Innovate LC-1 Wideband with XD-16 Gauge

Innovate LC-1 with Sensor, without Gauge$199

Innovate Standalone Gauge Kit w/ LC-1 & Blue DB Digital Gauge - $229

Innovate Standalone Gauge Kit w/ LC-1 & Red DB Digital Gauge$229

Innovate Standalone Gauge Kit w/ LC-1 and G2 Analog Gauge - $289

Innovate Standalone Gauge Kit w/ LC-1 and G3 Analog Gauge - $289

Innovate Standalone Gauge Kit w\ LC-1 & XD-16$329

 

Click Here if you have questions or would like to contact us!
 

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