Megasquirt on 205 GTI
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Thread: Megasquirt on 205 GTI

  1. #1
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    Default Megasquirt on 205 GTI

    I just got back from short test drive of my UK spec 205 GTI 1.9 with Megasquirt ECU (with MAP sensor) replacing the L Jetronic.
    It has not been tuned at all, I just left in the program that had worked in the 505 GTI but reduced overall fuel richness (so that the idle mixture was OK) to suit the different injectors, fuel pressure and of course engine.
    Even so there is a big improvement, better torque, 500 RPM better top end and much more drivable (no jerkiness etc.)
    Of course, much of this would be down to wear in the old L Jetronic system, but still very impressive, especially as there should be more to come.
    Graham

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  2. #2
    1000+ Posts Dave's Avatar
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    How hard is it to build one of these megasquirts?
    I'm pretty good with DIY jobs, and dad is an electronic engineer, so should be able to manage it. How does it control the idle?

    Cheers,

    Dave


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    Quote Originally Posted by Dave
    How hard is it to build one of these megasquirts?
    I'm pretty good with DIY jobs, and dad is an electronic engineer, so should be able to manage it. How does it control the idle?

    Cheers,

    Dave
    Unlike the Si (with stepper motor) the GTI has no special way of controlling idle speed at running temperature so the Megasquirt adds nothing to this.

    In the GTI the cold start idle speed is controlled by a water temperature controlled air valve and additionaly the mixture is richened by the ECU. The Megasquirt also enrichens the mixture until the engine has warmed up and simply takes advantage of the mechanical device for speed. The Megasquirt does have an output which can be used to trigger a solenoid operated fast idle air valve.

    If you can solder small components onto PCBs and have an understanding of electronics this is not a hard project. There is heaps of information and advice on the Megasquirt website.
    The kit costs $200 Aus and includes the MAP sensor. You will need to buy a Throttle Position Sensor, around $110, Air Temp sensor $15, and Oxygen Sensor $100. I managed to fit the ECU without adding any under dash wires, just the vacumn line for the MAP sensor. Of course you will need to have access to a lap top with serial port to tune it.

    Graham

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    1000+ Posts Dave's Avatar
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    mmm, just had a read about megasquirt 2 which controls ignition aswell. Ah well maybe i'll have a play next time i have a decent holiday.


    Thanks for the info,

    Dave


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    Quote Originally Posted by Dave
    mmm, just had a read about megasquirt 2 which controls ignition aswell. Ah well maybe i'll have a play next time i have a decent holiday.


    Thanks for the info,

    Dave
    Don't complicate things too much, the appeal of Megasquirt is its simplicity.
    If you set your sights too high you may never get around to actually doing anything.
    Graham
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    1000+ Posts parry's Avatar
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    How and where did you install the TP sensor, also why cant we use the standard oxygen sensor.

    I am asking as I am thinking of trying it as well on the 205 race car.
    90 205 Gti Cherry Red(Track Car)
    2009 207gti
    1985 505gti (Shitbox Rally) Sold

    PBs:

    Oran Park: 1:27:9
    Wakefield: 1:05.6 (July 2015)
    Eastern Creek: 1:54 (8v) 1:48 (16V)
    Mt Huntley: 34.44 (2004 stock 205)
    Ringwood: 35.06 (30/10/2005)
    Winton: 1:33.6 (2017)

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    Quote Originally Posted by parry
    How and where did you install the TP sensor, also why cant we use the standard oxygen sensor.

    I am asking as I am thinking of trying it as well on the 205 race car.
    Sorry, I forgot the local cars had oxygen sensors, probably worn out by now though.
    The TP Sensor mounts in the same spot as the original TP Switch. I had to shorten the throttle body spindle and make an aluminium adaptor plate.
    I have the part number of the TPS that I used if anyone is interested.
    Graham

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    i'm thinking of modifying a volvo setup to use megasquirt and nissan injectors

    i haven't gone through everything i need yet so im am looking hard at these threads to see what others are doing
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    Quote Originally Posted by pugrambo
    i'm thinking of modifying a volvo setup to use megasquirt and nissan injectors

    i haven't gone through everything i need yet so im am looking hard at these threads to see what others are doing
    This would be very interesting!
    I saw Graham converting his 505 GTI (L Jetronic) to Megasqirt and it was quite straightforward & reversible. He tuned it with his kids school laptop as I drove around.

    Was there ever a PRV V6 with L Jetronic - as this would be very simple to Megasquirt if you could get a manifold with injectors & Air flow meter.

    Didnt the Volvos use Lambda? Does this mean they had oxygen sensors for mixture control like the Pug 505 SLIs? Perhaps this could be incorporated.

    A very worthy project; so please keep us posted.
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    So many projects - so little time.

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    oxy sensors can be placed in the exhaust

    any other sensors will need to be put in place

    i think it all should work

    i will head out to the shed tomorrow and have a look through what i have

    i do have a complete early crab type volvo unit and a twin plenum setup but it's missing the fuel dissy for the mechanical injection

    i'd prefer to use the twin plenum setup if possible as it flows better
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    Quote Originally Posted by 604 tragic
    This would be very interesting!
    I saw Graham converting his 505 GTI (L Jetronic) to Megasqirt and it was quite straightforward & reversible. He tuned it with his kids school laptop as I drove around.

    Was there ever a PRV V6 with L Jetronic - as this would be very simple to Megasquirt if you could get a manifold with injectors & Air flow meter.

    Didnt the Volvos use Lambda? Does this mean they had oxygen sensors for mixture control like the Pug 505 SLIs? Perhaps this could be incorporated.

    A very worthy project; so please keep us posted.
    The even fire was the first to get EFI.
    The 505 V6 rally car which I have been involved with has an Autronic ECU fitted, more sophisticated than the Megasquirt as it controls spark as well.
    You don't have to use the O2 sensor if you don't want to but you will need to have the car dyno tuned and even then they like to use an O2 sensor.
    An exhaust shop will fit a mounting device on your exhaust pipe for $20 or so.
    Graham

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    Graham,
    Have you removed the airflow meter. If so are you still using standard induction system and aircleaner?

    Jarrod

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    Quote Originally Posted by jarrods
    Graham,
    Have you removed the airflow meter. If so are you still using standard induction system and aircleaner?

    Jarrod
    Yes, I am about to fit a length of 65mm diameter plastic tube (available from a hardware shop) to take its place!
    Graham

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    Default Oxygen sensor?

    Graham,
    WHat tyoe of oxygen sensor is able to be used with the Megasquirt.
    3 wire or1 wire??
    Chris
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    Quote Originally Posted by HONG KONG PUGGY
    Graham,
    WHat tyoe of oxygen sensor is able to be used with the Megasquirt.
    3 wire or1 wire??
    Chris
    Best to use 3 (4) wire as they don't have the warm up problems of the 1 (2) wire devices. The Megasquirt would be happy with the 1 wire otherwise .
    Graham

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    Graham, just as a point of interest;

    Do you have to put in a lookup table for the Lambda sensor, or does it just assume a linear transition between lean and rich.

    Also, is there any sort of compensation factor for different sensors?

    Ken

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    Here's the reference voltages for an NTK sensor:

    mV AFR
    900 11.5
    890 12
    860 12.5
    850 12.7
    820 13
    780 13.5
    710 14

    It's difficult to measure above 14:1 as there is a severe point of inflection around 14.7:1 (610mV). For best performance, you want to tune between 12.5:1 and 14:1 anyway. Best to use an analoque meter. Digital reacts too fast.

    I would imagine any narrow band sensor to be very similar.

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    Quote Originally Posted by AxGT
    Graham, just as a point of interest;

    Do you have to put in a lookup table for the Lambda sensor, or does it just assume a linear transition between lean and rich.

    Also, is there any sort of compensation factor for different sensors?

    Ken
    No calibrating required, the reading just comes up on the computer screen as a string of simulated LEDS, Red in the rich region and Green for lean. There is also a simulated analogue display of the EGO voltage. You can select closed loop mode where the EGO will control the mixture or open loop where it just follows the VE table exactly.
    As Peter says oxy sensors are all pretty similar.
    Graham

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