Engines covered:
Pre-Optispark small block Chevy V8s with TPI or TBI injection and HEI ignition with electronic spark timing (seven or eight pin HEI module)
Much of this article will apply to other 1980s era GM cars including injected big blocks and even fire V6s.
TPI and TBI
The Tuned Port Injection and Throttle Body Injection versions of the small block Chevy and used very different hardware, but similar electronics. Not only do they show up in many trucks such as the C1500 pickup, but also Camaros, Firebirds, and Corvettes, and other cars as well. Also these two injection systems are also very popular for swaps into street rods, S10 pickups, and muscle cars. This article will show you how to set this up whether you’re dealing with a car originally equipped with this engine or swapping it into a vintage machine.
For these engines, we recommend using the Megasquirt-II. This ECU installs on ’80s era GM engines like it was designed for them, which isn’t far from the truth since it comes pre-calibrated for all GM sensors. It can control a HEI ignition and the stepper motor idle control found on these engines using its standard hardware. For those of you who are looking to do a less expensive installation, you can use the Megasquirt-I, but this will not have provisions for controlling the IAC. When using a Megasquirt-I, you will need to adjust the idle speed screw to obtain a fast enough idle in cold weather.
We’ve recently developed a HEI mod kit that gives a stronger RPM signal in cars with noise problems. For the pre-mod kit version of this article, click here.
This article also mentions the relay board. While factory injected will not need this, the relay board is very helpful when you are swapping an injected motor into a car that never came with fuel injection from the factory.
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Note that this does not allow sequential injection, as HEI provides no cylinder identification. You do not need any mods to make this work.
External Ignition Wiring
- The R pin is the HEI module’s tach output. Connect it to pin 24 on the Megasquirt main board, or the Tach pin on the relay board. Note that the DIY Autotune wiring harness has a shielded wire – connect only the inner wire to this pin!
- Connect the E pin to MS3X pin 14 to send the timing signal to the HEI module.
- Connect the B pin MS3X pin 33.
- If you are using our wiring harness, connect the IAC using the four IAC wires. If you are using a relay board, the IAC wires will come out on terminals S1 through S4.
TunerStudio Ignition Configuration:
- Spark mode = Basic trigger
- Trigger angle / offset = 10 (this will vary, depending on the distributor orientation, see notes at the end of the article)
- Ignition Input Capture to ‘Rising Edge’
- GM HEI / DIS options to ‘GM Bypass on SpkB
- Spark hardware in use to MS3X spark
- Dwell type to ‘Standard dwell’
- Spark Output to ‘Going High’
Dwell depends on the coil; 2.5 to 3.0 ms is usually a good starting value.
More information on setting Trigger Offset:
You must also set the initial position of the trigger (called the ‘trigger offset’), then check it using the Trigger Wizard in TunerStudio (Tools Menu). The trigger offset setting will vary according to your distributor position (where it is in rotation) but you’ll need to set it properly… Basically you use the Trigger Wizard and adjust the ‘trigger offset’ and/or twist your distributor until the advance number in the Trigger Wizard matches what you’re reading with your timing light. The +/- buttons on the trigger wizard will adjust your trigger offset. You’ll need to use these buttons and a timing light to make the number on your light, and the big number on the left in the Trigger Wizard, match up.
Here’s the information on this:
Before tuning your advance table, be sure to use a timing light to verify that your ‘trigger offset‘ is calibrated. Changing the Trigger Offset in TunerStudio will not change the displayed advance, instead, it changes the actual advance as seen with a timing light. Your goal is to make these two match.
To do this, get your engine warmed-up (otherwise the timing moves as the temperature increases) and idling, then use a timing light to verify to be certain your actual advance as shown by a timing light equals your the advance display on the advance gauge in TunerStudio. (8, in this case). (Note that positive numbers denote BTDC, and negative numbers denote after TDC.)
For further reading, check out the MSExtra forum on GM HEI ignition modules. |
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This one can be used with both B&G code and MS2/Extra, although the settings aren’t quite the same as the ones in the regular MS2/Extra manual. For the version covered in the MS2/Extra manual, see this write up instead.
If you’re assembling your MegaSquirt-II from a kit (Part# MS230-K):
- For the most part, stick with the standard assembly documentation. We will cover any departures from that doc here.
- Step 22: You will want all of the IAC jumpers.
- The input mods are to invert the input signal from the HEI module’s tach signal. The HEI module will ground pin 24 to trigger a spark input.
- Remove D1 and D2, if they are installed. Replace them with jumpers.
- Remove the jumper between XG1 and XG2 and any jumper leading to TachSelect, if fitted.
- Run a jumper wire from TachSelect to XG1.
- Run a jumper wire from OptoIn to one of the two +5V holes in the Proto Area.
- Remove C30.
- Replace R12 with a 1.3k resistor. You may substitute a resistor from between 1 to 2 k.
- Jumper OPTOOUT to TSEL.
- Step 65: You will not be using the IGBT high current driver; you’re using a logic level ignition output instead. Jumper JS10 to IGN to bring the signal out on pin 36.
That’s it– you’ve got your Megasquirt-II Engine Management System fully prepared to work with a HEI ignition and stepper IAC.
If you’re using a DIYAutoTune.com MS2357-C MegaSquirt-II Assembled ECU:
- You will need to install our HEI input mod kit. This actually drops in without soldering on our current V3.57 boards; we have a YouTube video of how to install this kit. You will remove the JP1 and XG1-XG2 jumpers. Use the red jumper to connect the 5 volt pin next to the processor to JP1 pin 3, and the green jumper to connect XG1 to JP1 pin 2.
External Ignition Wiring
- The R pin is the HEI module’s tach output. Connect it to pin 24 on the Megasquirt, or the Tach pin on the relay board. Note that the DIY Autotune wiring harness has a shielded wire – connect only the inner wire to this pin!
- Connect the E pin to pin 36 (relay board terminal S5) to send the timing signal to the HEI module.
- For the B pin, you will be using a relay, as described in the MSExtra forum section on HEI modules. You will need to wire a relay so that the coil gets power from a wire that is energized with the key in the Run position but not Start. Run a wire from the VREF terminal on the relay board to one of the switch terminals of the relay, and run a wire from the other pin on the relay to the B pin on the HEI module.
- If you are using our wiring harness, connect the IAC using the four IAC wires. If you are using a relay board, the IAC wires will come out on terminals S1 through S4.
TunerStudio Ignition Configuration for B&G code:
- Trigger offset = 10 (this will vary, depending on the distributor orientation, see notes at the end of the article)
- Ignition Input Capture to ‘Falling Edge’
- Cranking Trigger to ‘Trigger Rise’
- Coil Charging Scheme to ‘Standard Coil Charging’
- Spark Output to ‘Going High (Inverted)’
TunerStudio Ignition Configuration for MS2/Extra:
- Spark mode = Basic trigger
- Trigger angle / offset = 10 (this will vary, depending on the distributor orientation, see notes at the end of the article)
- Ignition Input Capture to ‘Falling Edge’
- GM HEI / DIS options to ‘Off’ (because this configuration does not use the ECU controlled bypass
- Spark A output pin to JS10
- Dwell type to ‘Standard dwell’
- Spark Output to ‘Going High (Inverted)’
Dwell depends on the coil; 2.5 to 3.0 ms is usually a good starting value.
More information on setting Trigger Offset:
You must also set the initial position of the trigger (called the ‘trigger offset’), then check it using the Trigger Wizard in TunerStudio (Tools Menu). The trigger offset setting will vary according to your distributor position (where it is in rotation) but you’ll need to set it properly… Basically you use the Trigger Wizard and adjust the ‘trigger offset’ and/or twist your distributor until the advance number in the Trigger Wizard matches what you’re reading with your timing light. The +/- buttons on the trigger wizard will adjust your trigger offset. You’ll need to use these buttons and a timing light to make the number on your light, and the big number on the left in the Trigger Wizard, match up.
Here’s the information on this:
Before tuning your advance table, be sure to use a timing light to verify that your ‘trigger offset‘ is calibrated. Changing the Trigger Offset in MegaTune will not change the displayed advance, instead, it changes the actual advance as seen with a timing light. Your goal is to make these two match.
To do this, get your engine warmed-up (otherwise the timing moves as the temperature increases) and idling, then use a timing light to verify to be certain your actual advance as shown by a timing light equals your the advance display on the advance gauge in TunerStudio. (8, in this case). (Note that positive numbers denote BTDC, and negative numbers denote after TDC.)
Image courtesy of Bowling and Grippo
For further reading, check out MSeXTRA forum notes on stepper idle air control valves and GM HEI ignition modules. |
Using the MegaSquirt-II PCBv3.0 or V3.57 – New MS2/Extra setup
This version requires MS2/Extra, and has the ECU controlling the bypass pin based on engine RPM.
If you’re assembling your MegaSquirt-II from a kit (Part# MS230-K):
- For the most part, stick with the standard assembly documentation in the MS2/Extra manual. I’ll just be covering any departures from that doc here.
- You will want all of the IAC jumpers.
- Set it up for VR input by jumpering TachSelect to VRIN and TSEL to VROUT.
- For the main spark output, run a 1K resistor from the 5 volt source in the proto area or the right side of R24 to the top (negative) lead of D14, and run a jumper wire from the negative lead of D14 to IGN.
- For the bypass output, run a 1K resistor from the 5 volt source in the proto area or the right side of R28 to the top (negative) lead of D16, and run a jumper wire from the negative lead of D16 to SPR4 to bring this output out on DB37 pin 6.
That’s it– you’ve got your Megasquirt-II Engine Management System fully prepared to work with a HEI ignition and stepper IAC.
If you’re using a DIYAutoTune.com MS2357-C MegaSquirt-II Assembled ECU:
- Set it for VR input by putting the JP1 jumper (in the lower right hand corner of the main board) in the 1-2 position, and the J1 jumper (in the middle of the main board) in the 3-4 position.
- Remove the wire from JS10 to the center hole of Q16.
- Run a jumper wire from PAD1 to the center hole of the Q16 slot, and remove Q16 if fitted.
- Run a jumper wire from PAD3 to SPR4.
External Ignition Wiring
- The R pin is the HEI module’s tach output. Connect it to pin 24 on the Megasquirt, or the Tach pin on the relay board. Note that the DIY Autotune wiring harness has a shielded wire – connect only the inner wire to this pin!
- Connect the E pin to pin 36 (relay board terminal S5) to send the timing signal to the HEI module.
- Connect the B pin to pin 6. If using a relay board, this comes out on the small header next to the fast idle relay.
- If you are using our wiring harness, connect the IAC using the four IAC wires. If you are using a relay board, the IAC wires will come out on terminals S1 through S4.
TunerStudio Ignition Configuration:
- Spark mode = Basic trigger
- Trigger angle / offset = 10 (this will vary, depending on the distributor orientation, see notes at the end of the article)
- Ignition Input Capture to ‘Rising Edge’
- GM HEI / DIS options to ‘GM Bypass on D16’
- Spark A output pin to ‘D14’
- Dwell type to ‘Standard dwell’
- Spark Output to ‘Going Low’
Dwell depends on the coil; 2.5 to 3.0 ms is usually a good starting value.
More information on setting Trigger Offset:
You must also set the initial position of the trigger (called the ‘trigger offset’), then check it using the Trigger Wizard in TunerStudio (Tools Menu). The trigger offset setting will vary according to your distributor position (where it is in rotation) but you’ll need to set it properly… Basically you use the Trigger Wizard and adjust the ‘trigger offset’ and/or twist your distributor until the advance number in the Trigger Wizard matches what you’re reading with your timing light. The +/- buttons on the trigger wizard will adjust your trigger offset. You’ll need to use these buttons and a timing light to make the number on your light, and the big number on the left in the Trigger Wizard, match up.
Here’s the information on this:
Before tuning your advance table, be sure to use a timing light to verify that your ‘trigger offset‘ is calibrated. Changing the Trigger Offset in MegaTune will not change the displayed advance, instead, it changes the actual advance as seen with a timing light. Your goal is to make these two match.
To do this, get your engine warmed-up (otherwise the timing moves as the temperature increases) and idling, then use a timing light to verify to be certain your actual advance as shown by a timing light equals your the advance display on the advance gauge in TunerStudio. (8, in this case). (Note that positive numbers denote BTDC, and negative numbers denote after TDC.) |
Using the MegaSquirt-I (MS1/Extra)
These settings won’t give you control over the IAC valve, but it will let you take control of the ignition as well as fuel delivery. The MSExtra forum has detailed information about how to set up Megasquirt to work with an HEI ignition. This write-up uses slightly different pins to better work with the relay board.
MegaSquirt-I PCBv2.2 Mods Required:
- The input mods are to invert the input signal from the HEI module’s tach signal. The HEI module will ground pin 24 to trigger a spark input.
- Remove D5, D8, and R10.
- Replace D8 with a 1.3 k resistor. You may substitute a resistor between 1.3 k and 2.0 k.
- Remove the jumper from XG1-XG2. Jumper XG1 to the right (non-banded) side of D5.
- Solder a jumper from the lower hole where R10 used to be (the hole nearest U4) to the upper lead of R11. This will provide a 5 volt pull-up.
- You will use LED 17 and LED 19 as outputs.
- Solder a 1 k resistor from the negative lead of D17 (it’s marked with a small – sign) to the right lead of R23 to provide a 5 volt pull-up on the output.
- Run a wire from the negative terminal of D17 to jumper X12.
- Now you will add the equivalent mod to D19.
- Solder a 1 k resistor from the negative lead of D19 to the right lead of R27.
- Run a wire from the negative terminal of D19 to jumper X11.
- That’s it!
MegaSquirt-I PCBv3.0 Mods Required:
- The input mods are to invert the input signal from the HEI module’s tach signal. The HEI module will ground pin 24 to trigger a spark input.
- Remove D1 and D2, if they are installed. Replace them with jumpers.
- Remove the jumper between XG1 and XG2 and any jumper leading to TachSelect, if fitted.
- Run a jumper wire from TachSelect to XG1.
- Run a jumper wire from OptoIn to one of the two +5V holes in the Proto Area.
- Remove C30.
- Replace R12 with a 1.3k resistor. You may substitute a resistor from between 1 to 2 k.
- Jumper OPTOOUT to TSEL.
- You will use two LEDs as ignition outputs.
- Connect a 1 k resistor from the +5V source in the proto area to the negative lead of D14. The negative LED leads are marked with small – signs on the board.
- Run a jumper wire from the negative lead of D14 to the IGN jumper hole.
- Connect a 1 k resistor from the +5V source in the proto area to the negative lead of D16.
- Run a jumper wire from the negative lead of D16 to the IAC1A jumper hole.
- That’s it!
External Ignition Wiring
- The R pin is the HEI module’s tach output. Connect it to pin 24 on the Megasquirt, or the Tach pin on the relay board. Note that the DIY Autotune wiring harness has a shielded wire – connect only the inner wire to this pin!
- Connect the E pin to pin 36 (relay board terminal S5) if you have a V3.0 board. If you are using a V2.2 board, use pin 27 or relay board terminal S2.
- Connect the B pin to pin 25 (relay board terminal S1) with either board.
MSnS-E Ignition Configuration
- Under Codebase and Output Functions, set HEI Ignition to “GM 7pin HEI” and the other options to Off.
- Set LED 17 function to Spark Output A, and LED 19 function to Spark Output B.
- In Spark Settings, set the Trigger Angle to 10 degrees and set Spark Output Inverted to No.
- To set the timing with MSnS-E, go to the Spark Settings menu and set Fixed Angle to 10 degrees. You can then set the ignition timing to 10 degrees with the engine running, using a timing light. Once you have set the base timing, set Fixed Angle to -10. This will tell MSnS-E to use the timing map.
- Under dwell settings, set dwell type to dwell control. The dwell time will depend on the coil used. Typical values will be 3.0 to 4.0 ms.
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