Megasquirt wiring
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    1. #1
      Junior Member
      Join Date
      Oct 2012
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      19

      Megasquirt wiring

      Couple of questions for the experienced megasquirt installer. I am installing a MS 2, 3.57, on a 1971 P1800E with relay board and am a little confused. Do the wires for the stater solenoid - 18/29 need to be routed back tot he FIDLE relay? Does the cold start relay/valve still need to be used or is the MS controlling the cold start RPM? Any suggestions on how to wire and control a SPAL fan into the relay board? Can the trigger on the distributor be used for tach input or too unstable and would be better to just pull off of the negative on coil?

      Eric

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    3. #2
      Member
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      May 2013
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      Saskatchewan, Canada
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      I can't advise on the specifics of the relay board because I repurposed most of the existing D jet harness and used a main relay / fuse box from a Lexus E300 for most of my relays and fuses. The Lexus box fit better in the location where I wanted it, came with a weather tight lid that was retained by easily removable clips and looked like it belonged in the engine compartment.

      Now to the easy stuff.

      The D jet's cold start valve and associated relay are not used in an MS implementation. I am currently using the MSExtra code (I started out with the B&G firmware) so, depending on which firmware you are using things may be slightly different, but, should be pretty close. MS opens the injectors for a for defined period when you first turn the ignition key on to wet the intake manifold with a 'priming' pulse. Once you start cranking the engine MS switches to a temperature defined 'cranking' pulse width which injects fuel to each cylinder on each cylinder combustion cycle. The combination of the prime pulse and cranking pulses replace the function of the D jet cold start valve. You can blank the port for the cold start valve off with a piece of aluminum if you want to eliminate the valve. Don't throw the valve away. If it works you can probably sell it on Ebay to some other D jet owner who needs one - new replacements are very expensive.

      The connection from the starter solenoid is not required by MS. On the D jet, the cold start valve only injects fuel during cranking. It does not operate once the engine is running and has no role in controlling idle speed during engine warm up. Idle speed during engine warm up on the D jet is controlled by the auxiliary air valve which is mounted in the front of the head on a B20E or B20F engine. If your aux air valve still works, the easiest way to do warm up idle speed control is to continue to use the aux air valve. In this case, the FIDLE relay in the relay board will not be used for idle control. If your aux air valve is dead, then you will need to replace it with an simple idle air solenoid, a stepper solenoid or something like a Bosch 2 or 3 wire PWM idle air valve which take over the function of the aux air valve. The FIDLE relay can control a simple on off idle air solenoid. If you use a stepper type solenoid or a Bosch PWM idle air valve the FIDLE relay is not used in the idle control function. With the B&G MS firmware, the idle solenoid / idle air valve is temperature controlled. There is no direct engine speed control. With a simple on - off idle solenoid this gives you no additional speed or fast which gets faster as the engine warms up to the point that the MS shuts the solenoid off - much better to use the aux air valve if it still works. With the MSExtra firmware you can do closed loop engine speed control; but, don't even dream of attempting to do this until you have the engine set up and running well with a steady hot idle.

      If you use the Djet aux air valve for warm up idle control you can use the FIDLE relay to control your radiator fan. In Tuner Studio, click the Boost/Advance button on the top bar and then select Programmable On/Off Outputs on the drop down box. Select FIDLE under ports, tick Enable and then select the conditions. Your probably want the fan to turn on with a coolant temperature of around > 85 C with a hysteresis of 2 or 3 C (shuts off when the coolant drops to 85 - 3 = 82C). Select the additional condition of RPM >700 because you don't want the fan running unless the engine is running. If you are using the FIDLE valve for idle speed control, you can repurpose any one of the three LEDs (D14, D15, D16) or the IAC! and IAC2 outputs to control the relay for the fan. This does require some additional wiring / modifications on the mother board. I suggest that you get a .pdf copy of the MSExtra hardware manual

      http://www.msextra.com/manuals/

      It is not 100% applicable if you are not using MSExtra; but, because you can get it in .pdf form it can be a little easier to go through than the B&G on-line mega manual. The section on wiring up extra outputs should be 100% applicable.

      Do not attempt to use the old D jet trigger contacts to generate an RPM signal. Even if the pulse rate was correct (I have a feeling it isn't), there is no voltage present on those wires and you would have to modify the OPTO IN circuit with pull up resistors and other stuff to have it work. If you have a conventional coil arrangement with points or a Pertronix like ignition module taking the RPM signal off of the coil - terminal is easiest. I am presuming that you are doing batch fire fuel control with no ignition timing control? If you are thinking about doing ignition timing control, attempting to do ignition timing control on a distributor using the ignition points for spark timing is not advisable. The Tooth #1 Advance Angle required for ignition control results is a problem where the distributor rotor has poor alignment with the towers on the distributor cap resulting in weak spark or no spark under certain conditions.
      Last edited by 142 Guy; 01-27-2019 at 12:51 PM.
      A 142 of course. What do you expect? I'm the 142 guy. / 1971 142 E 102 color

    4. #3
      Junior Member
      Join Date
      Oct 2012
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      19
      Quote Originally Posted by 142 Guy View Post
      I can't advise on the specifics of the relay board because I repurposed most of the existing D jet harness and used a main relay / fuse box from a Lexus E300 for most of my relays and fuses. The Lexus box fit better in the location where I wanted it, came with a weather tight lid that was retained by easily removable clips and looked like it belonged in the engine compartment.

      Now to the easy stuff.

      The D jet's cold start valve and associated relay are not used in an MS implementation. I am currently using the MSExtra code (I started out with the B&G firmware) so, depending on which firmware you are using things may be slightly different, but, should be pretty close. MS opens the injectors for a for defined period when you first turn the ignition key on to wet the intake manifold with a 'priming' pulse. Once you start cranking the engine MS switches to a temperature defined 'cranking' pulse width which injects fuel to each cylinder on each cylinder combustion cycle. The combination of the prime pulse and cranking pulses replace the function of the D jet cold start valve. You can blank the port for the cold start valve off with a piece of aluminum if you want to eliminate the valve. Don't throw the valve away. If it works you can probably sell it on Ebay to some other D jet owner who needs one - new replacements are very expensive.

      The connection from the starter solenoid is not required by MS. On the D jet, the cold start valve only injects fuel during cranking. It does not operate once the engine is running and has no role in controlling idle speed during engine warm up. Idle speed during engine warm up on the D jet is controlled by the auxiliary air valve which is mounted in the front of the head on a B20E or B20F engine. If your aux air valve still works, the easiest way to do warm up idle speed control is to continue to use the aux air valve. In this case, the FIDLE relay in the relay board will not be used for idle control. If your aux air valve is dead, then you will need to replace it with an simple idle air solenoid, a stepper solenoid or something like a Bosch 2 or 3 wire PWM idle air valve which take over the function of the aux air valve. The FIDLE relay can control a simple on off idle air solenoid. If you use a stepper type solenoid or a Bosch PWM idle air valve the FIDLE relay is not used in the idle control function. With the B&G MS firmware, the idle solenoid / idle air valve is temperature controlled. There is no direct engine speed control. With a simple on - off idle solenoid this gives you no additional speed or fast which gets faster as the engine warms up to the point that the MS shuts the solenoid off - much better to use the aux air valve if it still works. With the MSExtra firmware you can do closed loop engine speed control; but, don't even dream of attempting to do this until you have the engine set up and running well with a steady hot idle.

      If you use the Djet aux air valve for warm up idle control you can use the FIDLE relay to control your radiator fan. In Tuner Studio, click the Boost/Advance button on the top bar and then select Programmable On/Off Outputs on the drop down box. Select FIDLE under ports, tick Enable and then select the conditions. Your probably want the fan to turn on with a coolant temperature of around > 85 C with a hysteresis of 2 or 3 C (shuts off when the coolant drops to 85 - 3 = 82C). Select the additional condition of RPM >700 because you don't want the fan running unless the engine is running. If you are using the FIDLE valve for idle speed control, you can repurpose any one of the three LEDs (D14, D15, D16) or the IAC! and IAC2 outputs to control the relay for the fan. This does require some additional wiring / modifications on the mother board. I suggest that you get a .pdf copy of the MSExtra hardware manual

      http://www.msextra.com/manuals/

      It is not 100% applicable if you are not using MSExtra; but, because you can get it in .pdf form it can be a little easier to go through than the B&G on-line mega manual. The section on wiring up extra outputs should be 100% applicable.

      Do not attempt to use the old D jet trigger contacts to generate an RPM signal. Even if the pulse rate was correct (I have a feeling it isn't), there is no voltage present on those wires and you would have to modify the OPTO IN circuit with pull up resistors and other stuff to have it work. If you have a conventional coil arrangement with points or a Pertronix like ignition module taking the RPM signal off of the coil - terminal is easiest. I am presuming that you are doing batch fire fuel control with no ignition timing control? If you are thinking about doing ignition timing control, attempting to do ignition timing control on a distributor using the ignition points for spark timing is not advisable. The Tooth #1 Advance Angle required for ignition control results is a problem where the distributor rotor has poor alignment with the towers on the distributor cap resulting in weak spark or no spark under certain conditions.

      Thank you, you are a true aficionado and single source encyclopedia for this information. I have read the majority of what you have advised others and it is inspiring.

      I will be setting the engine up with Batch fire, Pertronix ignition module, no ignition timing control yet.

      Thank you again.

      Eric

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    6. #4
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      May 2013
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      Saskatchewan, Canada
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      When you pull the tach signal off of the coil negative wire, be sure to keep the tach signal wire away from any of the high voltage leads. Make sure the coil tower is in good condition and the boot on the coil wire on the tower is in good condition and that the coil wire is in good condition. I had a new set of the fancy silicon IPD ignition wires on my car. There was a problem with the wire termination on the end that stuck into the coil tower. It resulted in the occasional internal flashovers under the boot.

      When I first set up MS2 I was running the B&G firmware with batchfire, no ignition control and using the coil negative for the tach signal. I was getting erratic ECU resets on the MS2 and I could not figure out where they were coming from. It wasn't till I was standing next to the running engine with the hood open, the laptop hooked up and I heard a little snap, the engine hesitated and sure enough the flag indicating a reset showed up on the laptop. The 'snap' came form the flashover on the coil terminal and the flashover somehow managed to generate a voltage on the coil negative terminal which showed up on the tach wire causing the ECU to reset. I replaced the high voltage wiring with a new set of OEM Bosch wires and the problem went away. Strangest things can screw you up.

      When I switched to MSExtra code I switched to a optical tach and cam sensor which eliminates the potential nasty stuff that can show up when using the coil negative for a tach signal.

      Cleanly done wiring, proper terminations with the correct crimping tool, isolated grounds for all the sensors running back to the MS2 box and a good ground to the engine block are critical. You will likely be using an O2 wideband sensor - make sure that the heater ground is a separate ground wire from the signal ground on the wideband controller. A lot of O2 controllers use pulse width modulation to control the heater and the currents can be fairly high. Pulse width can generate significant electrical noise and you don't want it showing up on the signal line.
      A 142 of course. What do you expect? I'm the 142 guy. / 1971 142 E 102 color

    7. #5
      Junior Member
      Join Date
      Aug 2018
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      24
      Stealthems...

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