MRT - Link ECU Tuning Tips

Thru the hundreds of ECU's that MRT Performance have fitted tuned and updated, we have found many ways of learning the hard way and learning also from others. Here we offer some limited data that will hopefully allow you to do some tuning of your own. Maybe it will assist you to do it yourself and save some time and money, maybe there is a trick upgrade that will make your car even better.

However at any time if you are unsure please contact us for advise.

DISCLAIMER: We accept no Liability whatsoever should you encounter any problems using this information.

97 98 Subaru Impreza WRX /GT model - Idle tips
If clamp figure is too low it will give poor idling as clamp is the point at which the ecu stops trying to read vacuum and controls fuel off only set zone mixtures. Generally about 40 to 50 works. That figure is actually vacuum in kpa. So if a car idles at 35 kpa with air con and lights etc 40 is good. Although for whatever reasons the car doesn't make that kind of vacuum at idle the figure needs to be slightly above what it makes. Every car is different in slight ways for various reasons, inc. engine condition and good or not so good intercooler design and size

97 98 Subaru Impreza WRX /GT model - Idle tips #2
ECU requires the idle motor to be adjusted to at, or as close to 30% duty cycle to function properly as the setting in both zones 18 and 19 are duty cycles which the ECU defaults to when the tps registers as being away from idle position. Hence if zone 18 (being Hot Idle) is at 34 (recommended) when away from idle it will default to 34% duty cycle and rpm , upon back off of throttle, should go to around 1100 (34% duty) and then slowly work its way back idle of around 900 (30% duty cycle). So if the base idle figure is at for example 50% duty upon back the idle will still default to what is set in to zone 18 and if it is lower than your actual idle duty cycle there absolutely no chance of being able to catch the rpm on its way down as the ECU has told it to do so. This is exactly the same theory with zone 19 (Cold Idle) although for obvious reasons it needs to be a higher figure, generally anywhere between 42 and 48 works fine depending on mods, intercooler design and cold start enrichment.

General tip
In no circumstance EVER adjust idle by releasing the throttle stop screws.
If you do wish to adjust the Throttle Position switch or re set from repair the position should read 10 in the TPS setting of the select zones and 100 for full throttle.
IF YOU DO MOVE The THROTTLE do this.
Always make sure throttle butterfly is closed then crack open 1/4 turn Adjust idle speed controller to 35 36% using hand controlled in adj idle screen (ver. 3 or 4 only) Then after that check hot idle settings ZONE 18 This should be approx 35 36 37 if its too high the idle will not drop. And will stay high too long. if it DOES NOT respond, then there is something wrong like above OR also check chocky brown relay under dash this is the ign relay and provides power to the idle speed motor
if the car is hard to start at cold this will be the same prob fit new relay OR back off the idle manually as a last resort.

General tip, or CAR will not fire or start on initial installation of new ecu
DIP switches on ecu board for OE immobiliser
If the switch is set incorrect immediately when Ignition is turned on the car will backfire out the exhaust
(even before the engine is cranked) Then there will be no spark at all for cranking If in doubt switch the switches the opposite way to test if your car does not start as in above NO HARM can be done with either setting.

General tip on use of lambda targets
LAMBDA TARGETS
MRT Performance don't recommend the sole use of Lambda targets, (zones 26, 27 28 29 30 & 31) basically because the factory O2 sensor is a narrow band device and the Ecu can not get an accurate reading and you CAN will end up with terrible settings. This feature may be used as a rough guide only. (MRTP suggests always aim rich!)

Unusual miss fire or running FACTORY o2 SENSOR
This sensor MUST be fitted and working otherwise poor performance will result.

Subaru Impreza WRX/GT ver. 5 6 with stepper motor idle control ZONE 17 (over run vacuum) general notes
This is the point where it registers what a trailing throttle is and it wont try to control idle typically set at 24 (24kpa) Idle is normally around 40kpa So on a training throttle when you back off the vacuum goes below 24kpa, the ECU will ignore the reading hence stopping it from trying to control idle via the idle control motor. This stops the engine from having a fluctuating idle when the situation occurs that you do end up at idle it wont have to massively re open the idle motor to compensate.

Subaru Impreza WRX/GT ver. 5 6 with stepper motor idle control ZONE 18
(default stepper motor figure for off idle position) general notes
These notes are only relevant to later model chips fitted to this ECU Typically a "magical" number of steps, and idle should be approx 60, so as this setting should be then set to 70 - 80. So when you step off the throttle the motor is at 70 - 80 and has not got far to move to a satisfactory idle setting.
The number in the idle screen in select zones, will be in brackets, is the number of steps at idle.

There is five symbols that also appear in this screen
neg (-) means the stepper motor is trying to pull idle down
pos (+) means the stepper motor is trying to pull idle up
V (V) means overrun vacuum condition, actual engine vac has gone below set amount (see notes on Zone 17)
T (T) means the throttle is off idle (and open)
= (=) means the idle has achieved the idle you chose
(IE if idle rpm (zone 8) was set to 800 and the car IS
idling @800 then (=) will appear)
NOTE re zone 8 idle rpm
The number displayed is double divided by 10
IE if idle is 800 the display is 16
IE if the idle is 1000 the display is 20

all Subaru models except 01/02 WRX. WASTE GATE BASE To set waste gate BASE
This is a GUIDE only
4th gear 80,90 km/hr
To set base go to waste gate base screen
Hit full throttle default number in brackets the lowest number
should equal roughly what the waste gate base number should be set at
this will be around 35 36 for 97 on incl ver. 5 (maybe 38 - 40)
for older models 95 96 with tdo5 turbo = 45
Liberty will be 41 with suss engine 50 or even 60
The higher the number effects turbo spool up (IE higher is faster) although if you go too, high it wont
hold the desired boost level it will over shoot (big time!) Basically set the number high until it wont hold a steady boost
WASTE GATE RPM
The level the wastage starts to open......
(WRX) approx 3000 rpm, any lower it wont catch the boost and it over boost

General notes MAP sensors
The OE sensors have weird mapping and are not interchangeable The cosworth unit (as at 6/3/00) is not suitable, ONLY the link unit is available or the high range "555" unit. Both available from MRT Performance

INTERFERENCE
Some models suffer this with the hand controller fitted, or the ribbon cable, remove and re test, IE spikes on tacho, etc etc Also mobile phones can cause it.

Subaru Impreza WRX/GT Series 5/6 2000 model Zone 17 18 19
The id hot setting ZONE 18 and 19 is redundant
Zone 17 is air tem / fuel compensation only for STi models with temp sender in air box/inlet

If you find some useful information, that others, or MRT Performance may
benefit of, please contact us via info@MRTrally.com.au

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