Petrol F20 – why does it fuel on the overrun?
Discussion
Just got a 2019 118i and am learning how it works.
If the live fuel consumption gauge can be trusted, some fuel continues to be fed into the engine on overrun.
Why might that be? Is it trying to raise the exhaust temperature for better GPF regen? Does this also happen on pre-GPF (pre-2018) F20s?
If the live fuel consumption gauge can be trusted, some fuel continues to be fed into the engine on overrun.
Why might that be? Is it trying to raise the exhaust temperature for better GPF regen? Does this also happen on pre-GPF (pre-2018) F20s?
Sorry for the slow reply. I didn’t get an email notification of your post.
Automatic. Speed well above idle, but maybe not much over 1500. Will have to see if it does this around 2000 RPM and up too – I think it does, from memory (that is, consumption drops to around 2.5 L/100 km rather than zero as I expected).
No big deal, but I’d like to know how my new car works and why.
Automatic. Speed well above idle, but maybe not much over 1500. Will have to see if it does this around 2000 RPM and up too – I think it does, from memory (that is, consumption drops to around 2.5 L/100 km rather than zero as I expected).
No big deal, but I’d like to know how my new car works and why.
Not sure if the F20 got the coasting function when ECO Pro is used (puts the transmission in neutral effectively and idles the engine rather than use the fuel cut-off), could it be this one? If not, perhaps the transmission is in too high a gear to engage the cut-off? I'll have a look at mine (3-series, B48 engine but autotrans too) to see when it cuts off.
My car does indeed have that coasting feature, but it was turned off (was in “Comfort” mode) and the car was driving the engine when I noticed this. Or so I thought!
How would the GPF regenerate if the car always coasts when it would otherwise overrun? Because the GPF needs oxygen to regen, something it won’t get from a petrol engine running under its own power.
I don’t have access to the car for a few days to check further. Would be curious to hear at what RPM your 3 Series cuts off the fuel … if it ever completely does.
How would the GPF regenerate if the car always coasts when it would otherwise overrun? Because the GPF needs oxygen to regen, something it won’t get from a petrol engine running under its own power.
I don’t have access to the car for a few days to check further. Would be curious to hear at what RPM your 3 Series cuts off the fuel … if it ever completely does.
Tried it on mine this morning, when the instantaneous consumption in the cluster -the Efficient Dynamics display- was showing "charge" (=cutoff to me), the other reading in the cluster menu showed 99.9mpg (have mine set to miles, I'll try km on my way back). This was in all gears I could try, and effectively from anything above high idle. It could be that that reading doesn't go over 99.9mpg (=2.8l/100km), does your ED display go to the blue section?
I'll hook my obd reader up to see what it's actually doing, but I suspect it's just the way the displayed calculation works.
I'll hook my obd reader up to see what it's actually doing, but I suspect it's just the way the displayed calculation works.
This continues to intrigue and slightly bother me.
When I take my foot off the accelerator pedal, I want appropriate engine breaking to occur (proportional to RPM). Instead, my car often continues to fuel the engine.
This often leads to the absurd situation where I’m dragging the brakes down a hill against a driving engine.
Why do car reviewers never talk about things like this? I have discovered so many little things about this car that should have been in every review.
Two things make me certain it really is feeding petrol to the cylinders on the overrun, and that it’s not just a calculation or display error:
1. On some occasions, the fuel-economy gauge drops all the way to 0 litres per 100 km, as I would expect every time.
2. On these occasions, engine breaking is noticeably stronger.
What I don’t understand is why it sometimes fuels and sometimes doesn’t. Both behaviours have happened with the engine cold or warm, in cold or warm weather, with the battery probably charged or probably a bit depleted, in automatic or manual shift mode, and with or without cruise control activated, at any RPM over a high idle.
Also, both behaviours have happened in all of the drive modes (Sport, Comfort, and Eco Pro if it decides not to coast in neutral).
Hmm.
When I take my foot off the accelerator pedal, I want appropriate engine breaking to occur (proportional to RPM). Instead, my car often continues to fuel the engine.
This often leads to the absurd situation where I’m dragging the brakes down a hill against a driving engine.
Why do car reviewers never talk about things like this? I have discovered so many little things about this car that should have been in every review.
Two things make me certain it really is feeding petrol to the cylinders on the overrun, and that it’s not just a calculation or display error:
1. On some occasions, the fuel-economy gauge drops all the way to 0 litres per 100 km, as I would expect every time.
2. On these occasions, engine breaking is noticeably stronger.
What I don’t understand is why it sometimes fuels and sometimes doesn’t. Both behaviours have happened with the engine cold or warm, in cold or warm weather, with the battery probably charged or probably a bit depleted, in automatic or manual shift mode, and with or without cruise control activated, at any RPM over a high idle.
Also, both behaviours have happened in all of the drive modes (Sport, Comfort, and Eco Pro if it decides not to coast in neutral).
Hmm.
Here’s a photo of the typical scenario, coasting down a long, shallow hill.
When the RPM is a bit lower, the consumption is also a bit lower (because of lower air-pumping losses) but still in the range of 2.5 litres per 100 km.
But sometimes (one in five times, maybe?) it will drop to zero.
Any ideas? I’m not suggesting something is wrong, just curious what the heck is going on.
When the RPM is a bit lower, the consumption is also a bit lower (because of lower air-pumping losses) but still in the range of 2.5 litres per 100 km.
But sometimes (one in five times, maybe?) it will drop to zero.
Any ideas? I’m not suggesting something is wrong, just curious what the heck is going on.
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