MAP sensor not plugged in to anything?!?! MK4 GTI, 1.8T, SMIC,

[tmh983]

dragging out this old thread.

So can anyone answer the question that how does the ecu sense load if the maf is not plugged in?
My agu runs fine without the maf, boost is lower, but apart from that you would be hard pressed to notice a difference in responsiveness and general running of the engine. So it must have some method of sensing the load??? I can't find a map sensor anywhere on the manifold and there is no map pressure readout in VCDS, so it can't be using speed-density mapping, does this mean it simply uses throttle position as its only measure of load?

[Transporter]

No it doesn't have to. It just uses the back up program for this situation (when the sensor(s) fails).

[tmh983]

No it doesn't have to. It just uses the back up program for this situation (when the sensor(s) fails).

No it doesn't have to what? The ecu back up program still needs a method of sensing the engine load. It can't just guess at the correct injection and ignition timing...
Most other ecus i've seen run static injection timing on primary load sensor failure, this dictates that you can't run the engine under high load or rpm, it injects just enough fuel to keep the engine running and thats all, hence the term limp home mode. The agu ecu MUST have a method of calculatinginjection and ignition timing when the maf fails, and to do that, it must have a method of sensing engine load.

[aprr32]

How about throttle position V engine speed?

[tmh983]

throttle position mapping doesn't work too well in turbo cars because the air flow rate is not predictable enough. If u plant ur foot, initially there is no boost until the turbo responds, so the air flow is low, as the boost pressure rises, so does the airflow and therefore fuel requirement. but the throttle is still in the same position - so throttle position alone is not really enough information to accurately calculate fuel requirement (it can be made to work on non-turbo cars, but isn't used often as it is too sensitive to environmental changes ie. heat, humidity, changing the flow rate for a given throttle position).

[h100vw]

throttle position mapping doesn't work too well in turbo cars because the air flow rate is not predictable enough. If u plant ur foot, initially there is no boost until the turbo responds, so the air flow is low, as the boost pressure rises, so does the airflow and therefore fuel requirement. but the throttle is still in the same position - so throttle position alone is not really enough information to accurately calculate fuel requirement (it can be made to work on non-turbo cars, but isn't used often as it is too sensitive to environmental changes ie. heat, humidity, changing the flow rate for a given throttle position).

If the MAF is bad for whatever reason, boost is restricted and it goes off what it knows. Throttle position. The fact that it isn't a very accurate way of determining flow is why they run rich.

Also the reason that the ME7 has a MAP sensor as well as MAF.

Gavin