Friday night. Five minutes in to what was sure to be yet another three hour crime spre.. ahem.. 'cruise', I suddenly heard a soft pop of complaint from the quad exhaust, my dash lit up like a Christmas tree, and my throttle response all but disappeared to the chime of the car's diagnostic warning tone. Bing..... Bing..... The red line on the tacho came crashing down from 8250 to 4450rpm like a fụcking anvil!
My focus was immediately drawn from the road ahead to the great big blinking yellow engine icon front and center of the dash binnacle.
"Oh great!", I exclaimed to no one in particular as I lifted my foot off, what was at the time, about twenty percent of full throttle..
During all this I was entering one of the many round-abouts near my abode. This afforded me the opportunity to turn around and head back toward the garage. As I dialed in more lock than originally planned, I was once again subjected to what was quickly becoming the most annoying sound in the world. Bing... Bing...
This time it was the I-Drive system informing me of more impending doom.
Good to know that I had no Dynamic Stability Control now too. Especially worth considering as the car had already entered a heavily restricted limp mode and the power on tap had become, for want of a better term, embarrassingly low. Honestly, where I had suddenly found myself, it was highly doubtful that DSC was going to be called upon to do anything but whinge.
Whilst I limped back towards home, the exhaust note sounding somewhat odd, I quickly navigated to the control messages information screen on the I-Drive and found the following issues listed.
Some additional information, but not really anything more specific.
I got home, parked up, and broke out the trusty Schwaben Scan Tool.
A few minutes later I was feeling somewhat more relaxed as the scan tool had quickly pointed me in the direction of the nature of the fault at hand.
The car was throwing a fit because one of the throttle actuators (there are two of them) that drive the ten independent throttle butterfly valves of the S85 was misbehaving itself.
This is a fairly common fault on M3, M5 and M6 vehicles of the era that sport these drive by wire systems.
I also looked into the DSC and Start Assist systems, they had gone offline due to a lack of input from the DME (ECU). This car has some forty-seven separate control sub modules (computers) that are heavily interdependent due to the level of automation inherent in the vehicle. Presumably the missing input was that of throttle position, specifically those throttles on bank two, which on RHD cars, is on the passenger side of the engine.
Further investigation into the issue using live data diagnostics and activation tests revealed that the actuator on bank two had suffered catastrophic electronic failure, no drive/control current was being fed to the little motor that opens a bank of five throttles. No sound could be heard from the engine bay when running the passenger side bank through its paces. In stark contrast the whir of the electric actuator could be clearly heard when probing the bank on the driver's side.
The two images below paint a fairly desperate picture:
No pressure on the throttle pedal provides exactly what you would expect. Zero percent throttle actuator position on both banks.
With the pedal fully depressed (engine off), you get a clear idea of why they car wanted back home, and was making such a fuss about it happening as quickly as possible. Zero percent on the left, and close to one-hundred percent on the right bank. In hindsight, I am quite suprised that the engine was running at all, let alone relatively smoothly.
So... $911.20 later, I have ordered a replacement pair of throttle actuator units, and am expecting them to arrive from the United Kingdom in the next couple of weeks. In the meantime I will be tackling the removal of the current ones. I will post updates as they become available. It should be somewhere around three hours of work for the change-out.
That is all I have for now. The engine bay awaits my attention.
Peace!