How long does it take for an ecu to "learn" SUL?
Discussion
My Octavia vRS is supposed to be run on 98 octane but for several years I've run it on 95 - it goes fine. SWMBO recently started a new job which requires that I collect her at night after her shift as there's no public transport there at 10pm.
The journey doesn't vary much - 15 miles there, mostly clear motorway (M9), and 15 miles back on mostly 60 mph single carriageway and 30 mph in town.
I started to check my fuel consumption and on the trip there - when I'm in no hurry and setting the cruise about 55mph - I regularly average on the trip computer 40-41 mpg. The journey doen't vary much and neither does the consumption.
Last week I decided to experiment, and as the car was nearly empty, filled it up with Tesco 99 (£77!
). I then monitored the consumption. Throughout the week it was at least 2 mpg WORSE than on 95.
Yesterday I had to fill it again. 95 octane. Back up to 41 mpg last night!
Have I given the ecu enough time to "learn" the SUL? I'd have thought that 50-odd litres and getting on for 400 miles should have done it.
The journey doesn't vary much - 15 miles there, mostly clear motorway (M9), and 15 miles back on mostly 60 mph single carriageway and 30 mph in town.
I started to check my fuel consumption and on the trip there - when I'm in no hurry and setting the cruise about 55mph - I regularly average on the trip computer 40-41 mpg. The journey doen't vary much and neither does the consumption.
Last week I decided to experiment, and as the car was nearly empty, filled it up with Tesco 99 (£77!
). I then monitored the consumption. Throughout the week it was at least 2 mpg WORSE than on 95.Yesterday I had to fill it again. 95 octane. Back up to 41 mpg last night!
Have I given the ecu enough time to "learn" the SUL? I'd have thought that 50-odd litres and getting on for 400 miles should have done it.
The ecu will play with timing all the time on boost but cruising along it wont make a difference ecu igntion learn wise as you wont get a car to det/pink on cruise. Therefore ignition learn wise its not going to effect your mpg.
Fuelling adjustments in basic terms are done in two ways, instantly in the short term memory and over time if the short term adjustment is to an extreme (adding fuel, or removing fuel) then it will adjust the long term learn.
The main effect on you mpg will be the fuel trims and adjustments, the ecu uses one or more lambda sensors to measure the amount of unburnt fuel and air in the exhaust fumes to work out what the fuelling was in the cylinder and then makes adjustments.
It is aiming on cruise for 14.7:1 air to fuel ratio (AFR) which is stoich for petrol and gives least emissions and best chance for cats to remove hc and co from the fumes.
It will roll around that number.
The thing is tesco 99 contains an amount of ethonal to increase the ron to 99. In basic terms ron influences how long it takes the fuel mix to explode under compression once ignited by the spark. The earlier in the compression stroke you ignite the fuel, the larger the flame will build to before exploding with a bigger bang (ignition advance see ignition learning earlier).
The problem is ethonal has a different stoich point to petrol so although it will give more power with the extra ignition advance because the ecu is targetting stoich of petrol and stoich of ethonal is different the ecu injects a small amount extra fuel on the tesco99 when on cruise.
On boost the ecu wot use the lambda sensor to adjust the fuelling other than the overall long term learn it gains from cruise.
Therefore of you drove it hard you might notice after a tank or so the extra power and be able to accellerate to your cruise speed quicker and with less throttle and therefore fuel injected.
But because you are trickling along it is unlikely to do more than what you are noticing.
Try esso98 as I believe it doesnt contain ethonal. But I doubt in this particular situation it wont make any difference.
Simon
Fuelling adjustments in basic terms are done in two ways, instantly in the short term memory and over time if the short term adjustment is to an extreme (adding fuel, or removing fuel) then it will adjust the long term learn.
The main effect on you mpg will be the fuel trims and adjustments, the ecu uses one or more lambda sensors to measure the amount of unburnt fuel and air in the exhaust fumes to work out what the fuelling was in the cylinder and then makes adjustments.
It is aiming on cruise for 14.7:1 air to fuel ratio (AFR) which is stoich for petrol and gives least emissions and best chance for cats to remove hc and co from the fumes.
It will roll around that number.
The thing is tesco 99 contains an amount of ethonal to increase the ron to 99. In basic terms ron influences how long it takes the fuel mix to explode under compression once ignited by the spark. The earlier in the compression stroke you ignite the fuel, the larger the flame will build to before exploding with a bigger bang (ignition advance see ignition learning earlier).
The problem is ethonal has a different stoich point to petrol so although it will give more power with the extra ignition advance because the ecu is targetting stoich of petrol and stoich of ethonal is different the ecu injects a small amount extra fuel on the tesco99 when on cruise.
On boost the ecu wot use the lambda sensor to adjust the fuelling other than the overall long term learn it gains from cruise.
Therefore of you drove it hard you might notice after a tank or so the extra power and be able to accellerate to your cruise speed quicker and with less throttle and therefore fuel injected.
But because you are trickling along it is unlikely to do more than what you are noticing.
Try esso98 as I believe it doesnt contain ethonal. But I doubt in this particular situation it wont make any difference.
Simon
I stand to be corrected here, but I don't think it actually 'learns' anything.
The ECU (or rather, more accurately, the ignition module) will advance the ignition to the point of 'knock' as detected by the knock sensors. This will allow different octane ratings to be used to their maximum advantage.
I suspect that if the engine is feeling 'sweet', the temptation is to exploit more of the performance, hence using slightly more fuel.
Edit to add: The poster above makes a very valid point about the stoichiometric point of ethanol being different to petrol. The lambda will pick this up as mixture weakness and increase the fuel/air ratio to suit. Good point well made!
The ECU (or rather, more accurately, the ignition module) will advance the ignition to the point of 'knock' as detected by the knock sensors. This will allow different octane ratings to be used to their maximum advantage.
I suspect that if the engine is feeling 'sweet', the temptation is to exploit more of the performance, hence using slightly more fuel.
Edit to add: The poster above makes a very valid point about the stoichiometric point of ethanol being different to petrol. The lambda will pick this up as mixture weakness and increase the fuel/air ratio to suit. Good point well made!
Edited by littleredrooster on Tuesday 24th April 20:17
Edited by littleredrooster on Tuesday 24th April 20:18
My Octavia VRS is a Mk. 1 and seems to alter itself quite quickly.
Runs like a dream on nothing but V Power. But if I drive like Miss Daisy for a bit, and then suddenly go into mentalist mode, it seems to be fluffy for about 5 or 10 minutes, and then seems to go 'oh ok, I see what you're doing here, you want full power, right?!' And starts pulling like a train.
If I am somewhere and I need fuel but there's not a Shell garage available, I put in whatever other SUL there is, and it notices straight away - far less power and you can feel immediately that it has retarded the ignition and dropped the boost.
Once V power is back in the tank, I would say it takes 10 minutes of driving for the low power condition to disappear and it go back into a full power map.
HTH
Runs like a dream on nothing but V Power. But if I drive like Miss Daisy for a bit, and then suddenly go into mentalist mode, it seems to be fluffy for about 5 or 10 minutes, and then seems to go 'oh ok, I see what you're doing here, you want full power, right?!' And starts pulling like a train.
If I am somewhere and I need fuel but there's not a Shell garage available, I put in whatever other SUL there is, and it notices straight away - far less power and you can feel immediately that it has retarded the ignition and dropped the boost.
Once V power is back in the tank, I would say it takes 10 minutes of driving for the low power condition to disappear and it go back into a full power map.
HTH
Thats unlikely to be ecu learn you are feeling.
Driving the car gentle and in normal driving will soot the pistons, plugs etc and a blast will clear it out, also on a turbo charged car, when the exhaust section of the turbo is hotter it will spool earlier and make a little most boost and therefore feel quicker.
Cruising about itis unlikely to remove timing and therefore add it again on boost and the on boost fuel adjustment is only relayed in the long term learn from cruise.
Really learning is the wrong description for it as it doesnt really learn to your driving at all.
It adjusts to fuel quality.
Driving the car gentle and in normal driving will soot the pistons, plugs etc and a blast will clear it out, also on a turbo charged car, when the exhaust section of the turbo is hotter it will spool earlier and make a little most boost and therefore feel quicker.
Cruising about itis unlikely to remove timing and therefore add it again on boost and the on boost fuel adjustment is only relayed in the long term learn from cruise.
Really learning is the wrong description for it as it doesnt really learn to your driving at all.
It adjusts to fuel quality.
Ray Luxury-Yacht said:
My Octavia VRS is a Mk. 1 and seems to alter itself quite quickly.
Runs like a dream on nothing but V Power. But if I drive like Miss Daisy for a bit, and then suddenly go into mentalist mode, it seems to be fluffy for about 5 or 10 minutes, and then seems to go 'oh ok, I see what you're doing here, you want full power, right?!' And starts pulling like a train.
If I am somewhere and I need fuel but there's not a Shell garage available, I put in whatever other SUL there is, and it notices straight away - far less power and you can feel immediately that it has retarded the ignition and dropped the boost.
Once V power is back in the tank, I would say it takes 10 minutes of driving for the low power condition to disappear and it go back into a full power map.
HTH
Runs like a dream on nothing but V Power. But if I drive like Miss Daisy for a bit, and then suddenly go into mentalist mode, it seems to be fluffy for about 5 or 10 minutes, and then seems to go 'oh ok, I see what you're doing here, you want full power, right?!' And starts pulling like a train.
If I am somewhere and I need fuel but there's not a Shell garage available, I put in whatever other SUL there is, and it notices straight away - far less power and you can feel immediately that it has retarded the ignition and dropped the boost.
Once V power is back in the tank, I would say it takes 10 minutes of driving for the low power condition to disappear and it go back into a full power map.
HTH
jason s4 said:
As much as im sure SUL does provide some improvement in acceleration, i dont believe it improves much on smaller engined cars, even turbo charged.
Having said that, they do run a lot smoother.
Run smoother as the timing might not be taken out everywhere, the engine might be more prone to detonation at a certain rpm and therefore the ecu pulls timing there but not at another rpm so it doesnt feel smooth and also more ignition makes an engine more effiecent and has greater power and therefore smoothiness. Having said that, they do run a lot smoother.
JollyGrnMonster said:
Thats unlikely to be ecu learn you are feeling.
Driving the car gentle and in normal driving will soot the pistons, plugs etc and a blast will clear it out, also on a turbo charged car, when the exhaust section of the turbo is hotter it will spool earlier and make a little most boost and therefore feel quicker.
Cruising about itis unlikely to remove timing and therefore add it again on boost and the on boost fuel adjustment is only relayed in the long term learn from cruise.
Really learning is the wrong description for it as it doesnt really learn to your driving at all.
It adjusts to fuel quality.
Hmm, could be I guess!Driving the car gentle and in normal driving will soot the pistons, plugs etc and a blast will clear it out, also on a turbo charged car, when the exhaust section of the turbo is hotter it will spool earlier and make a little most boost and therefore feel quicker.
Cruising about itis unlikely to remove timing and therefore add it again on boost and the on boost fuel adjustment is only relayed in the long term learn from cruise.
Really learning is the wrong description for it as it doesnt really learn to your driving at all.
It adjusts to fuel quality.
Ray Luxury-Yacht said:
My Octavia VRS is a Mk. 1 and seems to alter itself quite quickly.
Runs like a dream on nothing but V Power. But if I drive like Miss Daisy for a bit, and then suddenly go into mentalist mode, it seems to be fluffy for about 5 or 10 minutes, and then seems to go 'oh ok, I see what you're doing here, you want full power, right?!' And starts pulling like a train.
If I am somewhere and I need fuel but there's not a Shell garage available, I put in whatever other SUL there is, and it notices straight away - far less power and you can feel immediately that it has retarded the ignition and dropped the boost.
Once V power is back in the tank, I would say it takes 10 minutes of driving for the low power condition to disappear and it go back into a full power map.
HTH
Runs like a dream on nothing but V Power. But if I drive like Miss Daisy for a bit, and then suddenly go into mentalist mode, it seems to be fluffy for about 5 or 10 minutes, and then seems to go 'oh ok, I see what you're doing here, you want full power, right?!' And starts pulling like a train.
If I am somewhere and I need fuel but there's not a Shell garage available, I put in whatever other SUL there is, and it notices straight away - far less power and you can feel immediately that it has retarded the ignition and dropped the boost.
Once V power is back in the tank, I would say it takes 10 minutes of driving for the low power condition to disappear and it go back into a full power map.
HTH
In that case, to answer the OP - dunno!
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