How to MegaSquirt Your Dodge Neon or Other Car With the Chrysler 420A Engine

Applications: This works for the first generation Chrysler / Dodge / Plymouth Neon (both SOHC and DOHC motors), second generation Diamond Star cars (Mitsubishi Eclipse or Eagle Talon) with the 420A motor, and several other applications of this motor such as the various “cloud cars” (Chrysler Cirrus, Plymouth Breeze, and Dodge Stratus) in both 2.0 and 2.4 liter variations, and 2001-2002 PT Cruisers (later ones use the “second generation Neon” settings). This can also be used for second generation Neons, including the SRT4, with slightly different settings detailed in this write-up.

This write-up uses the BIP373 coil drivers instead of the HEI modules mentioned in the Extra documentation. The VB921s around when the Extra documentation was written would burn up if you tried to get enough dwell out of the coils. BIP373s don’t have this problem.

Using the QuadSpark on a Megasquirt-III V3.0 or V3.57 Board with MS3X

Hardware setup required:

This one uses the VR conditioner for input. On a V3.0, jumper TachSelect to VRIN and TSEL to VROUT. On a V3.57, put main board jumper JP1 in the 1-2 location and J1 in the 3-4 location. Install the cam pull-up jumper (JP7) on the MS3X card.

External wiring:

  • Connect the crankshaft position sensor to pin 24 of the main board DB37 connector.
    • This sensor needs a pull up. There are several ways to do this:
    • External pull up: Wire a 1K resistor in between pins 24 and 26 in the main board wiring harness.
    • Internal pull up on a V3.0: Solder a 1K resistor to a length of wire and connect it from TachSelect to S5.
    • Internal pull up on a V3.57: Install a 1K resistor in the R57 slot.
  • Connect the camshaft position sensor to pin 32 of the MS3X DB37 connector.
  • You’ll wire up the QuadSpark according to the MS3 QuadSpark directions. Spark A goes to cylinders 1 and 4, and spark B to cylinders 2 and 3.
  • Injector A goes to cylinder 1, B to cylinder 3, C to cylinder 4, and D to cylinder 2.

 

TunerStudio settings required:

Under Ignition Options / Wheel Decoder:

  • Set Spark Mode to “420A/Neon” (Second generation Neons: Use “36-2+2” instead.)
  • Set the trigger angle / offset to 0.
  • Set Ignition Input Capture to “Rising Edge.”
  • Set Spark Output to “Going High (Inverted).” Setting this wrong can overheat the QuadSpark or damage the coils.
  • Set Number of Coils to “Wasted Spark.”
  • Set Spark Hardware in Use to “MS3X spark.”
  • Set Cam input (If used) to “MS3X Cam in.”
  • Set Dwell Type to “Standard Dwell.” Start with 4.0 ms dwell; this may need to be adjusted depending on your coil.

 

Direct Coil Control Distributorless Ignition on a Megasquirt-II V3.0 or V3.57 Board

Using MS2/Extra firmware, version 2.0.0 or higher

Hardware mods required:

If you’re building this from a kit, be sure you add the stepper IAC jumpers.

V3.0 input mods:

  • Remove C30.
  • Replace R12 with a 470 ohm resistor.
  • Wire the top hole of C30 to S5 or the 5 volt spot in the proto area.
  • Jumper TachSelect to XG1 (remove the XG1-XG2 or TachSelect to anything else jumpers, if fitted)
  • Jumper TSEL to OptoOut.

V3.57 input mods:

  • Remove C30.
  • Remove the pull-off jumpers from XG1 to XG2 and in the JP1 slot.
  • Put the main board J1 jumper in the 1-2 position.
  • Use a jumper such as the one in our jumper.1 package to connect the 5 volt spot by the boot jumper to the #3 hole of JP1.
  • Use another such jumper to connect XG1 to the #2 hole of JP1.

Now for constructing the outputs…

  • Install a BIP373 transistor with a mica insulator in the Q16 slot. For a V3.0 board, jumper IGN to IGBTOUT.
  • 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.
  • Heatshrink wrap this wire/resistor assembly.
  • 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. (On a V3.57, this is kind of tricky. It’s easier to use pin 7 on the U1 socket instead.)
  • Now, you will be constructing duplicates of this BIP373 circuit for each coil output you need. You will be using outputs A and B. You can mount the additional BIP373s on a second heat sink stacked on top of the first, attached on top with long screws. Or you can mount the BIP373s to the case.
  • Each BIP373 will need a resistor-on-a-wire assembly, running to its left leg. You will get the BIP373 input signal from the following locations:
OutputInput Location (V3.0)Input Location (V3.57)
Spark ATop of R26U1 pin 7
Spark BTop of R29U1 pin 8
  • The center leg of the BIP373 is its spark output. This one uses the stepper IAC connections, so we’ll need to use the SPR wires for spark output B. Wire the center leg of the second BIP373 to SPR4, then flip the board over and wire SPR4 to pin 6 of the DB37. The SPR traces are too thin to carry the current on their own, so you have to reinforce them
  • Connect the right leg of the second BIP373 to a ground, such as the proto area ground or SG pins. It’s best if you can find a separate ground for each BIP373.
  • Second generation Neons have a PWM idle control valve. Use these mods if you are running a V3.0 on one of these:
    • Remove Q20 and D8.
    • Remove R39 and install a jumper in its place.
    • Install a TIP120/121/122 in place of Q4. For more information, see our MK-PWMIAC page.
  • V3.57 boards and first generation Neons do not need the PWM idle control mod.

External wiring:

  • Connect the crankshaft position sensor sensor to pin 24.
  • Use DB37 pin 36 for spark output A (cylinders 1 and 4) and 6 for spark output B (cylinders 2 and 3)

 

TunerStudio settings required:

Under Ignition Options:

  • Set Spark Mode to “420A/Neon” (Second generation Neons: Use “36-2+2” instead.)
  • Set the trigger angle / offset to 0.
  • Set Ignition Input Capture to “Falling Edge.”
  • Set Spark Output to “Going High (Inverted).” Setting this wrong can overheat the BIP373s or damage the coils.
  • Set Number of Coils to “Wasted Spark.”
  • Set Spark A output pin to “D14.”

Under Dwell Settings:

  • Set Dwell Type to “Standard Dwell.” Start with 4.0 ms dwell; this may need to be adjusted depending on your coil.

 

Direct Coil Control Distributorless Ignition on a Megasquirt-I V3.0 or V3.57 Board

Using MS1/Extra firmware – Does not support second generation Neon!

Hardware mods required:

V3.0 input mods:

  • Remove C30.
  • Replace R12 with a 470 ohm resistor.
  • Wire the top hole of C30 to S5 or the 5 volt spot in the proto area.
  • Jumper TachSelect to XG1 (remove the XG1-XG2 or TachSelect to anything else jumpers, if fitted)
  • Jumper TSEL to OptoOut.

V3.57 input mods:

  • Remove C30.
  • Remove the pull-off jumpers from XG1 to XG2 and in the JP1 slot.
  • Put the main board J1 jumper in the 1-2 position.
  • Use a jumper such as the one in our jumper.1 package to connect the 5 volt spot by the boot jumper to the #3 hole of JP1.
  • Use another such jumper to connect XG1 to the #2 hole of JP1.

Now for constructing the outputs…

  • Install a BIP373 transistor with a mica insulator in the Q16 slot. For a V3.0 board, jumper IGN to IGBTOUT.
  • 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.
  • Heatshrink wrap this wire/resistor assembly.
  • 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. (On a V3.57, this is kind of tricky. It’s easier to use pin 7 on the U1 socket instead.)
  • Now, you will be constructing duplicates of this BIP373 circuit for each coil output you need. You will be using outputs A and B. You can mount the additional BIP373s on a second heat sink stacked on top of the first, attached on top with long screws. Or you can mount the BIP373s to the case.
  • Each BIP373 will need a resistor-on-a-wire assembly, running to its left leg. You will get the BIP373 input signal from the following locations:
OutputInput Location (V3.0)Input Location (V3.57)
Spark ATop of R26U1 pin 7
Spark BTop of R29U1 pin 8
  • The center leg of the BIP373 is its spark output. Wire the spark output on the second BIP373 to IAC2B.
  • Connect the right leg of the second BIP373 to a ground, such as the proto area ground or SG pins. It’s best if you can find a separate ground for each BIP373.

External wiring:

  • Connect the crankshaft position sensor sensor to pin 24.
  • Use DB37 pin 36 for spark output A (cylinders 1 and 4) and 31 for spark output B (cylinders 2 and 3)

 

TunerStudio settings required:

Under Codebase and Output Functions

  • Set Neon / 420A decoder to “Neon / 420A.” Set all other code types to off.
  • Set LED17/D14 function to Spark Output A and LED19/D17 function to Spark Output B. Turn all other spark outputs off.

Under Spark Settings:

  • Set Trigger Angle to 69 degrees with zero trigger angle addition.
  • Set Cranking Timing to Trigger Return.
  • Set Spark Output Inverted to Yes. Setting this wrong can overheat the BIP373s or damage the coils.

Under Dwell Settings:

  • Set Dwell Type to “Dwell Control.” Start with 4.0 ms dwell; this may need to be adjusted depending on your coil.

Other things the ECU controls

Air Conditioning: MS3 can use its dedicated A/C control code. On other versions, you may control this with a relay.

Alternator control: You’ll need to add an external voltage regulator to control this. A lot of older Mopars use one that you can adapt. The MS3 code incorporates a “high speed field switching” mode that can also control the alternator.

Automatic transmission: The four speed automatic transmission is controlled by the ECU. If you have one of these, you will need to retain the stock ECU for transmission control, or use a MegaShift. Note that the three speed automatic used on SOHC Neons is mechanical. You would just need an on/off output to trigger the lock up torque converter.

Cooling fans: These can be run with a relay control mod or MS3X output.

Fuel pump: Use MegaSquirt pin 37 to control the relay.

Gauges: On the cloud cars, the ECU controls the gauges over a network, so we recommend leaving it in place for gauge control. On the Neon and DSMs, the only ECU controlled gauge is the tachometer. The MS3X’s built in tachometer control can run this. You can modify the ECU for tachometer control if you’re running an MS1 or MS2. See the tach output circuits in the MS1/Extra and MS2/Extra guides.

Idle speed: First generation Neons use a stepper IAC that you can control with either the MS2 or MS3 stepper IAC outputs. MS1 does not control the factory IAC valve. Second generation Neons replaced the stepper IAC with a PWM type.

What to Order

Here’s what we recommend for MS3.

MS330-K MegaSquirt III V3.0 Kit and MS3X expansion card, or MS3X357-C_BL complete MS3 with MS3X

QuadSpark ignition module

JimStim-K JimStim kit or JimStim-C complete JimStim, and StimPower power supply

MSHarness12 12′ wiring harness and MS3X-Harness wiring harness for MS3X board

TuneCable6 serial cable or MS3TuneCable USB tuning cable

 

If you’re buying an assembled MS2 unit, it will need special mods to work with the ignition, as described above. We can install these for you for an extra charge; please contact us for details.

If you’re building your unit from a kit, here is what we recommend for MS2:

MS230-K MegaSquirt II V3.0 Kit

MK-BIP373 to add extra coil driver

MK-RelayCtrl for relay outputs, as needed

MK-PWMIAC if installing on a second generation Neon

JimStim-K JimStim kit

MSHarness 12′ wiring harness (If you are wiring up a kit car from scratch, you could instead use a relay board, relay cable, and 12′ wire bundle, as shown on the kit car on this page)

TuneCable6 serial cable

USB-2920 if your computer doesn’t have an adapter port

If you are doing a parallel installation, we also recommend giving the MS its own coolant and air temperature sensors:

CLTIATwPiggy Closed element CLT sensor

IATwPiggy Open element IAT sensor

We also recommend a wideband oxygen sensor system for tuning.

DIYAutoTune is an MegaSquirt EMS/EFI manufacturing and distribution company.