22-03-2020, 09:44 PM
Hi Ed,
This was a pretty new car at the time, and it was a one-off incident caused entirely by software. It stopped as normal immediately before this, then when it restarted, it went mad. Pressing the start/stop switch had no effect because the ECU wasn't responding to normal inputs because it was in some weird state. Once the engine had been forcibly stalled and then restarted in the normal way, it behaved perfectly, and never did it again (we kept the car for several years after this). It wasn't running on its own oil, and I'm confident that if it had a normal ignition switch that shut the fuel pump off with no software involved, then it would have stopped just fine.
I'm sure it wouldn't have happened if auto stop-start was not being used to turn the engine on and off literally every few seconds. Think of the electrical disturbances that happen during and immediately after cranking - it's remarkable that computers in cars are as reliable as they are, frankly. That poor battery and starter motor must have been really suffering on that journey.
I've seen sources suggesting how long you need to be stationary before auto start-stop causes any tangible savings in fuel, and it's a figure that ranges from 10-60 seconds, depending on who you believe - and of course there are lots of assumptions and generalisations behind those figures. All of which ignores the extra wear on the starter and battery, and you only have to replace the starter once to wipe out any savings in fuel you might have made over the years.
Obviously it's a different thing for hybrids with their generator-based starters, but expecting a standard starter motor to reliably do this for 20 years is optimistic at best.
I accept that these systems might improve air quality in town centres, but only if drivers change their habits and stop creeping forwards an inch at a time every few seconds - easier said than done! I guess most don't care because their car is on a lease or PCP deal for the duration of the warranty, so mechanical sympathy is not something they need to worry about.
This was a pretty new car at the time, and it was a one-off incident caused entirely by software. It stopped as normal immediately before this, then when it restarted, it went mad. Pressing the start/stop switch had no effect because the ECU wasn't responding to normal inputs because it was in some weird state. Once the engine had been forcibly stalled and then restarted in the normal way, it behaved perfectly, and never did it again (we kept the car for several years after this). It wasn't running on its own oil, and I'm confident that if it had a normal ignition switch that shut the fuel pump off with no software involved, then it would have stopped just fine.
I'm sure it wouldn't have happened if auto stop-start was not being used to turn the engine on and off literally every few seconds. Think of the electrical disturbances that happen during and immediately after cranking - it's remarkable that computers in cars are as reliable as they are, frankly. That poor battery and starter motor must have been really suffering on that journey.
I've seen sources suggesting how long you need to be stationary before auto start-stop causes any tangible savings in fuel, and it's a figure that ranges from 10-60 seconds, depending on who you believe - and of course there are lots of assumptions and generalisations behind those figures. All of which ignores the extra wear on the starter and battery, and you only have to replace the starter once to wipe out any savings in fuel you might have made over the years.
Obviously it's a different thing for hybrids with their generator-based starters, but expecting a standard starter motor to reliably do this for 20 years is optimistic at best.
I accept that these systems might improve air quality in town centres, but only if drivers change their habits and stop creeping forwards an inch at a time every few seconds - easier said than done! I guess most don't care because their car is on a lease or PCP deal for the duration of the warranty, so mechanical sympathy is not something they need to worry about.
