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

Hardware setup required:

This application 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.

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:

• 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.

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:

• 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.