Rover Gauge Airflow reading

[V8Mad]

Seems a bit low at 3%? This is on warm idle...



Paperwork that came Rover Gauge suggested should range between 32-35% at idle. She has difficulty holding a steady idle from cold, as in RPM varying between 500-2000 RPM. Wonder if there's a loose connection? Any Rover gauge/14CUX experts here that could clarify if the above looks 'normal'?

Thanks

Edited by V8Mad on Tuesday 21st June 21:58

[blitzracing]

You are in the wrong mode- "Linear". This converts the AFM signal to a one the ECU can use to meter the fuel that removes the logarithmic response to airflow that the hot wire AFM exhibits. Select "direct" to get a decent reading at idle as per the notes. The rest looks OK, but check the long term trim as well- this will show any underlying fuelling issues if the values are high.

Edited by blitzracing on Wednesday 22 June 09:44

[davep]

All the RG screenshots I've seen show 'Linear' MAF reading as 4 to 6% at idle rising to 34 - 36% when engine is blip revved. IMO your screenshot looks fine.

RG Help file states:

MAF reading: Displays the reading from the mass airflow sensor as a percentage of its maximum range. This display has two modes:

Linear: Shows a percentage of the maximum airflow. It will vary linearly as the sensor measures more mass.

Direct: Shows a percentage of the maximum sensor voltage (5VDC). It will vary logarithmically as the sensor measures more mass.

For example, in Direct mode if idle is showing 30% the ECU is reading 1.5 Vdc from the AFM at idle.

Edited by davep on Wednesday 22 June 09:57

[blitzracing]

The advantage of direct mode is you get a far wider voltage swing around the idle point with very small changes in airflow, so its easier to get an accurate reading without the results being "compressed" into linear mode. Problem is AFMs do fail (I think due to heat) , and typically the output will go higher than needs be, resulting in high fuel trims or over fuelling, but this is easy spotted in direct mode as the output will be far out of spec'. It should be in the region of:

1.62 volts for a 3.9 litre engine or 32.4 %
1.75 volts for a 5 litre engine or 35%

The reading will depend on the idle RPM, and these vary a bit depending on the engine application and ECU map. The TVR idle is a bit higher than the Range Rover, so within a couple of percent of these readings should be OK- it will be a long way out if the AFM has failed, and this should also show up with very high long term fuel trim as well. Interestingly I dont use the lambda feedback (green map) and I get significant mixture shifts at idle after a long run, so I need to carefully monitor the idle voltage AFM on mine to see if this moves with temp. You wont see this effect on the catalyst map as the ECU simply moves the trim value to get the mixture correct again.

[davep]

^^^^^^
Thanks for that Blitz.

Edited by davep on Wednesday 22 June 11:48

[V8Mad]

Brilliant, thanks guys - will have to change the setting from linear to direct then and report back.