What sensor inputs does the ECU use in Open Loop Mode?

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May 29, 2002 | 06:25 PM

Brent V

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What sensor inputs does the ECU use in Open Loop Mode?

and also, when does the ECU kick into open loop? is it above a certain RPM in addition to WOT or is there some other threshold that I'm not aware of.

I'm trying to test all sensors that give input to the ECU to determine if I have a faulty piece of hardware or my software just isn't tuned correctly and I'd rather not have to test more sensors than I really have to.

Thanks,
-Brent
2000 1.8TQMSX +K04 and other stuff

May 30, 2002 | 04:00 AM

Electron Man

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Re: ECU inputs used in Open Loop Mode...

...for Drive By Wire(DBW) engines , ECU determines the throttle is wide open by monitoring the throttle position potentiometers in the throttle body (inside stepping motor enclosure). ECU responds to a WOT condition (ignoring the O2 sensors) regardless of rpm.

Once the ECU sees WOT, it looks at Manifold Absolute Pressure (MAP) and Mass Air Flow (MAF) sensor values to determine air mass. Once air mass is determined, ECU uses preprogrammed values to determine fuel delivery (injector pulse width).

There are also sensors (knock-two and intake air) that the ECU monitors when deciding how much timing advance to use. Ignition timing control is independent of throttle position.

May 30, 2002 | 08:03 AM

Brent V

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Does ecu go open loop under any other circumstance besides WOT?

..like above a certain RPM or anything like that? Does coolant temp sensor get taken into account during open loop or is it only intake air temp sensor?

Thanks!!

-Brent

May 30, 2002 | 09:47 AM

Audiboy

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a little clarification on the motronic system for the 1.8T and 2.7TT, the "map sensor"

or proper term, charge pressure sensure is located before the throttle body (on the intercooler for the 1.8T) and is mainly used to monitor and control boost. I'm assuming this signal may also be used by the ECU for determining fuel and timing specially at WOT were the pressure difference before and after the TB is about zero. But the real main players are the MAF as you pointed out, the air temp and water temp (in open loop). Manifold pressure can be derived knowing air temp and mass.

May 31, 2002 | 01:00 AM

dingster

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Yah.. coolant temp and intake temp is taken into consideration

Especially for timing and fuel control. Montronics also monitors EGT. There's even fuel enrichment when EGT climbs too high.

Audiboy is right about the MAP sensor. There is no MAP sensor. There's a boost sensor that pretty much serves as a feedback for closed loop boost control in dbw cars. On nondbw cars boost control is load based so it's entirely dependant on load calculated from MAF readings.