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Rb25Det Vct With Microtech Ecu

JetVL

By JetVL,
in Engines & Forced Induction

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Rolls Grand Master

Rolls

Posted
Posted

you always need to disable O2 feedback whilst tuning, then re-enable it once you're done.. however I just leave it off completely on the idle/cruise cells.

Yeah I mean leave it off and manually tune stoich at cruise? Doesn't it make it impossible to get it right all year around, eg humidity, altitude changes temperature etc?

Dose Pipe Sutututu Grand Master

Dose Pipe Sutututu

Posted
Posted

Yeah I mean leave it off and manually tune stoich at cruise? Doesn't it make it impossible to get it right all year around, eg humidity, altitude changes temperature etc?

that's right, but how often are you going to drive to the alps? lol

and remember, RB25DETs and SR20s don't have an intake air temp sensor so you can't correct much anyway.

If you're concern about all those factors just tune it to stoich, then re-enable the O2 feedback.. however I do find that the stock ECU takes a while to stoich hence I just leave it off usually

GTSBoy Grand Master

GTSBoy

Posted
Posted

Altitude and temperature should have no impact except maybe that as you go up in elevation then the turbo has to work harder to get the same boost, so exhaust manifold back pressure will increase and the compressed air temperature should also increase, which might require some richening of the mix to stave off pinging.

Humidity will have an effect, but it is probably smaller than the resolution of tuning anyway - or at worst only about like having the mixtures 0.3 or so :1 wrong. Well I'd hope so, without knowing for sure. But there is not a massive range in the mass% of water in air between 0% and 100% RH. At normal temperatures (like 20-30°C) you can only hold about 3% water in air at 100% RH. So assuming you tune near the middle of that range then you only have a possible swing of +/- 1.5% or so from where you tuned it. Enough to be noticeable perhaps, not enough to cause big dramas.

Dose Pipe Sutututu Grand Master

Dose Pipe Sutututu

Posted
Posted

I got a microtech and my idle control valve works and my revs increase when I turn on ac

it's not closed loop however it "may" appear to work correctly but it's far from perfect

sky30 Mentor

sky30

Posted
Posted

it's not closed loop however it "may" appear to work correctly but it's far from perfect

You set your desired idle rpm, and it will control the valve to acheive that rpm, air con on it can idle up. Never had an issue with mine either.

  • Like 1
SkudR33 Proficient

SkudR33

Posted
Posted

Closed loop idle control and closed loop mixture control are 2 different things anyway.

Lol to be honest I got no idea what closed loop idle control is - I read it doesn't increase idle when you turn on ac, so I argued that mine does....

Can someone provide a brief explanation of what closed loop idle control and mixture is?

Ben C34 Grand Master

Ben C34

Posted
Posted

Lol to be honest I got no idea what closed loop idle control is - I read it doesn't increase idle when you turn on ac, so I argued that mine does....

Can someone provide a brief explanation of what closed loop idle control and mixture is?

Closed loop briefly explained is it aims for a target, checks result, adjusts accordingly.
Rolls Grand Master

Rolls

Posted
Posted (edited)

Lol to be honest I got no idea what closed loop idle control is - I read it doesn't increase idle when you turn on ac, so I argued that mine does....

Can someone provide a brief explanation of what closed loop idle control and mixture is?

Closed loop idle control means a feedback loop eg ignition_adjustment = (ideal idle speed - actual idle speed) * tuning factor

Eg it is constantly adjusting the idle speed based on it's current speed by adding or subtracting both fuel and ignition.

Same with closed loop O2 feedback, it constantly adjusts the fuel at cruise to obtain stoich 14.7:1 air to fuel ratio, eg the injector pulse adjustment = (14.7 - current o2 reading) * tuning factor

The equation is more complicated than that as you actually have a PID controller with 3 tuning factors, but for discussion sake it is essentially that simple.

You can quickly see if you have a error, eg the idle is greater/less than the idle speed you want, it will then add/subtract ignition timing to slow/speed up the idle.

Open loop is where there is no feedback, it just depends on the map of ignition/fuel values, eg great for the conditions you tuned in, but as soon as you switch the A/C on or get the motor really cold/hot it doesn't work.

Edited by Rolls
GTSBoy Grand Master

GTSBoy

Posted
Posted

Just to be clear......real closed loop idle speed control is executed through an idle speed control valve, be that a stepper motor, PWM valve, or whatever. This actually is equivalent to opening and closing the throttle a little bit.

All the ECU does is open the valve a little more if the idle speed is lower than target, and vice versa.

If you have ignition control influencing idle speed, it's kinda technically closed loop idle speed control, because the ECU is at least trying to keep the idle on target, but because the tool being used (ie advancing or retarding the ignition timing) is a bit of crude way to control idle speed, it can't necessarily guarantee good speed control.

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