::: nBlog :::
I’ve been servicing our 2003 Saab 9-5 Aero myself for the past few years, mostly out of technical interest but recently also since Saab no longer exists as an automobile manufacturer, sadly enough.
The 2.3 liter, flexible fuel turbocharged engine is managed by an onboard computer called Trionic 7, which adjusts fuel injection, air flow, boost pressure, ignition timing, lambda values and various other parameters, based on tens of different measurements around the engine, but also including outside air temperature and pressure. Some of these values are now delivered to BaseN Platform, in real time.
The Trionic core is all about “maps”, which are predefined curves defining optimal adjustments correlating with different driving conditions. In modern cars, most tuning happens through these maps, even without hardware modifications.
Last week I exchanged the turbocharger, as it was leaking tiny amount of oil to the intake piping, causing issues with valves in the throttle housing. It had, anyway, served well for 380.000 kilometers; more than expected.
After some 4 hours the new turbocharger was installed, oil-primed and ready for a test drive. Initially, everything seemed fine, except for a longer-than-expected boost pressure ramp-up. I assumed the turbocharger right from Mitsubishi factory required some adaptation to fully spin up.
When the issue didn’t go away after some 50km, I enabled the diagnostic interface (Saab enthusiasts call it Open SID) and realized that the mReq (requested airmass) and mAir (actual airmass) didn’t follow each other, especially during the said boost ramp-up. As the intake piping is a semi-closed circuit, this was a clear indication that some air was getting in (and out) past the airflow meter next to the air filter.
And yes, I had slightly misplaced the large intake pipe toward the turbocharger. After re-sealing it the engine was like new again.
What was interesting though was that the Trionic did not consider this as a major issue by lighting up the ‘check engine’ warning or issuing a fault code, even though fuel consumption was significantly higher than normal. mAir and mReq thresholds must be fixed to allow for quite some leaks.
These relaxed thresholds are due to local memory and processing constraints. When these values are sent to our platform, it’ll be far easier to make accurate diagnoses based on much larger datasets. In this particular case, it would have been very simple to detect a major change in mReq/mAir ratio after swapping the turbocharger.
This operation again made me think more about our eHealth initiatives (and my aging), as it happens that many cardiovascular issues can be detected by.. the ratio of requested airmass (oxygen) by brain/heart and the amount lungs can actually deliver. Then there are numerous other parameters like blood pressure, haemoglobin, adrenalin.. just add the Platform to analyze all this.