Wiring Megasquirt into a Punto GT
Parts Needed
Empty GT ecu case
Megasquirt plug
Wire
Heatshrink
Solder
30-40 Ohm 50w Resistor - Used to hold the Idle control Valve shut
12v 30-40amp automotive relay - Used To activate the engine control relay
The wiring
I suppose its time to give away some wiring secrets, I can't guarantee my wiring so anyone using it does so at there own risk.
Ok here goes.
Gt pin 37 to megasquirt pin 28 - This is a switched live that is given power by the engine control relay.
Gt pin 12 to MS pin 26 - Throttle Position Sensor 5v Referance
Gt pin 30 to MS pin 19 - Sensor grounds
Gt pin 53 to MS pin 22 - TPS signal
Gt pin 44 to MS pin 20 - IAT sensor signal
Gt pin 45 to MS pin 21 - Coolant Temp signal
These next two should be wired with a sheilded twisted pair cable to minimise interferance.
Gt pin 47 to MS pin 2 - Crank sensor ground
Gt pin 48 to MS pin 24 - Crank sensor signal
The two above might need to be reversed if the signal is wrong
Gt pin 3 to Ms pin 37 - Fuel pump
Gt pins 16 and 17 to MS pins 34 and 35 - Injectors one and two
Gt pins 34 and 35 to MS pins 32 and 33 - Injectors three and four
I split the stripped ends of one thick wire and used it for each of the above
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Gt pin 1 to MS pin 6 - Coil for cylinder 1 and 2 Only of your using spr4 for the second coil output, If not then use whatever MS pin you connected the second ignition output to.
Gt pin 20 to MS pin 36 - Coil for cylinder 3 and 4
To run the GTs Idle control valve with MS you need to install the diode that came with the PWM Idle kit between pin 37 (+) and pin 4 in the GT ecu casing. This stops any voltage spikes/feedback into the MS from the valve while it is being used.
Gt pin 4 to MS pin 30, this is for idle control
Gt pin 22 to ground through a 30 to 40 ohm 50w resistor, this holds the ICV shut like an electrical spring, the MS can overpower this and open the ICV to increase the idle speed.
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Connect the coil of a 12v 30-40 amp relay to pin 27 of the Gt and ground, this will be energised whenever the ignition is on.
Connect the normally open contacts of the relay to ground and pin 36 of the Gt, this will provide an earth to the engine control relay whenever the ignition is on. This will switch 12v on for the injectors, Megasquirt and the fuel pump relay etc.
Now the coils are directly controlled you must unplug the old coil driver/ignition amplifier or it will be damaged, Bridge pin one and pin seven together and pins 2 and 6 together, this connects the MS directly to the coilpack. Looking at the connector from above the pins go 1234567. If you are making the megasquirt permanent then you can cut off the plug and solder the wires.
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For the grounds I soldered them all to a strip of metal in the original ecu case.
GT pins 14,24,19 are Ground
MS pins 8,9,10,11 and 18 are to be Grounded
Connect the ground of your wideband controller with the megasquirt earths
Connect the 0-5v of the wideband to MS pin 23
Set up your Tacho output in Tunerstudio then connect the ms output to GT pin 6 - This will get the original rev counter working.
Completed Wiring
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You can unplug and remove the AFM as it is no longer used.
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Back in 2007 when I did this I had some problems and solved them with this
Ok some extra information for anyone having problems with the VR circuit on megasquirt.
A few modifications have been shown to help with tach triggering issues:
1. If you experience tach drop-outs at higher rpms when using the VR input circuit, you might need to replace the diode D24. The issue is with the reverse recovery time of a 1N4001, its in the 30µsec region. You can use a 1N4148 diode (1N4148DICT-ND from Digi-Key) which is much faster and should solve this problem. This became the 'standard build configuration' in October of 2008.
2. You can remove the capacitor C32. This is the capacitor in parallel with R47. Although removing this capacitor may cause a ever-so slight phase shift, it will probably not be noticeable.
3. You can use a 0.001µF capacitor in C31 (instead of a 0.1µF capacitor) which may help with high frequency signals (such as high tooth count wheels). Many later kits (post-October 2008) come with a 0.001µF capacitor as standard.
Make sure that your crank trigger is right! use the tooth logger, you should only get one spike for each turn of the trigger wheel.
Myself I removed the capacitors C31 and C32 and it cured all the holding back and missfire problems, i'm going to try a 0.001 capaciter in C31 and see what happens. (Turns out I already had a 0.001 capacitor in place of C1, I put this back and it still runs well with this and with no cap in C2)
Or buy a VR conditioning board such as:
http://www.diyautotune.com/catalog/z...ers-p-378.html
http://forum.jbperf.com/viewtopic.php?f=6&t=78
VR conditioning circuits are available on ebay usually.
