Old fuel - how did the car know?

[gred]

As a non techie, can someone explain the following please.

I have a Peugeot 3008 Hybrid, a year old, and has a funny life. Sits at the airport for periods, then an hour's drive to home where the next two or three weeks runs almost exclusively on electric. Then another run down to the airport, rinse and repeat.

So in the last year it has been topped up with fuel a handful of times but on the present trip after charging the car overnight it ran under engine power with a brief message along the lines of 'old fuel, hybrid not available'. So for the last couple of weeks I've run the fuel down to the warning light and filled up this morning.

Immediately (I mean pulling out of the filling station) the car reverted to electric power and is now running hybrid perfectly.

So my question is (if you haven't fallen asleep yet), how does the engine management system know? Sensor of some sort?

I'm curious as the dealer, who coincidentally did an unrelated software update yesterday, didn't seem to know, just said to come back if it didn't sort itself out. I suspect they hadn't come across this before.

Thanks in advance

[paradigital]

I'd imagine it's something as simple as the fuel level sensor detecting an increase rather than decrease in level, possibly above a certain % of the tank threshold.

Cars have reset trip computers after filling up for at least a decade, so using that information on a hybrid to know that the fuel could be going stale isn't the greatest technological leap.

[snotrag]

It knows how many miles its done/how long its been since the fuel level went up, thats all.

[otolith]

All the mentions online of this issue seem to relate to the 3008, I wonder if any other hybrids do it? (Or whether they do it but don't tell you)

[SuperPav]

snotrag said:

It knows how many miles its done/how long its been since the fuel level went up, thats all.

I suspect it's as simple as this, but I too have not seen this in any other car!

[super7]

Probably in the same way as the ECU can tell the difference between super-unleaded and bog standard unleaded.

Old fuel will not burn as well which I guess will be noticed by the O2 sensors and knock sensors????

[GeniusOfLove]

Car knows when it's been filled up from the in tank level sensor going up, they used the same system to dose diesel with that "eolys" DPF additive on every refuel. I suppose they could use knock detection and moan when it has to pull timing but that could give you confusing messages if the car is knocking and pulling timing for some other reason, why overcomplicate things?

It's quite sensible really to avoid people keeping the same fuel in the tank until it gets bad enough to affect running, I'd expect every PHEV to do something similar.

[SkodaIan]

paradigital said:

I'd imagine it's something as simple as the fuel level sensor detecting an increase rather than decrease in level, possibly above a certain % of the tank threshold.

Cars have reset trip computers after filling up for at least a decade, so using that information on a hybrid to know that the fuel could be going stale isn't the greatest technological leap.

Even that might be more complicated than it actually is. It could be even more simple as being based on when the fuel filler flap was last opened.
My previous car had a check oil level warning (handy given how much oil it used!) which triggered when the oil was low but not critically so. Once on it would remain latched on even if the oil level was actually ok. It gave a false alarm from time to time when being parked on a steep slope and the oil was at the other end of the sump to the sensor. It was reset by opening and closing the bonnet, even if you hadn't put any more oil in.

[gred]

I'm not sure it's a fuel level sensor as our routine is to fill the car before each trip to the airport (about half a tank) so the last time was in March and January and December prior to that. Yet this is the first time we've had this happen.

Anyway, thanks for the various ideas.

[Megaflow]

It could be done from the level sensor, but it could also me a quality sensor.

Some DEF system's have a quality sensor that works by firing an ultrasonic beam across a fixed distance and measuring the time for it to return. By doing this you can calculate the density of the fluid and check it matches what it should be.

I don't know if the density of petrol/diesel changes with age, but it is an example of how you can measure these things.

[Fr0dders]

super7 said:

Probably in the same way as the ECU can tell the difference between super-unleaded and bog standard unleaded.

Old fuel will not burn as well which I guess will be noticed by the O2 sensors and knock sensors????

This. Modern engine management systems can detect quality of the fuel from their various sensors to work out knock levels etc... Your car just has a pre-programmed error to display on the screen when this happens.

[J4CKO]

super7 said:

Probably in the same way as the ECU can tell the difference between super-unleaded and bog standard unleaded.

Old fuel will not burn as well which I guess will be noticed by the O2 sensors and knock sensors????

Not sure the ECU can tell the difference can it ?

Am no expert but my limited understand is that it will advance (and retard) the ignition based on the ignition spark advance tables in the engines ECU map and using the knock sensor will retard it if it detects any detonation (pre-ignition or pinking as it used to be known)

[Krikkit]

In reality it's probably a combination of multiple sensors and triggers - they'll undoubtedly use knock detection, but it might not trigger the "old fuel" warning. It'll also likely have a flex-fuel sensor in the system to detect ethanol, petrol and water content of the fuel.

Then finally it'll have a little trigger in the system to register the previous fill-up, percentage filled and remaining percentage of old fuel. So, for example, if you put 10L in, wait a few weeks, then 5L twice it'll know there's less old fuel than putting 10L followed by 20L.

J4CKO said:

super7 said:

Probably in the same way as the ECU can tell the difference between super-unleaded and bog standard unleaded.

Old fuel will not burn as well which I guess will be noticed by the O2 sensors and knock sensors????

Not sure the ECU can tell the difference can it ?

Am no expert but my limited understand is that it will advance (and retard) the ignition based on the ignition spark advance tables in the engines ECU map and using the knock sensor will retard it if it detects any detonation (pre-ignition or pinking as it used to be known)

Modern ECUs are running right on the edge of knock, injecting as little fuel as they possibly can to extract maximum performance and fuel efficiency. Closed-loop knock control lets the ECU establish the best area to run in, and does it continuously...

ETA: A bit more info here: https://motorsport-developments.co.uk/Understandin...

Edited by Krikkit on Tuesday 16th May 16:29

[AlexIT]

Fr0dders said:

super7 said:

Probably in the same way as the ECU can tell the difference between super-unleaded and bog standard unleaded.

Old fuel will not burn as well which I guess will be noticed by the O2 sensors and knock sensors????

This. Modern engine management systems can detect quality of the fuel from their various sensors to work out knock levels etc... Your car just has a pre-programmed error to display on the screen when this happens.

But in this case I'd imagine it would throw out a message along the lines of "Fuel quality problem"; the fact that OP mentioned "old fuel, hybrid not available" makes me think that it's just a simple warning which is triggered if the car doesn't register a fuel level increase for a given amount of time.

[kalniel]

Krikkit said:

Modern ECUs are running right on the edge of knock, injecting as little fuel as they possibly can to extract maximum performance and fuel efficiency. Closed-loop knock control lets the ECU establish the best area to run in, and does it continuously...

I thought they had to run at a fixed fuel:air ratio for regulations? (Except on WOT when they're allowed to run rich for protection)

[Bobupndown]

Witchcraft

[PositronicRay]

On a dual fuel vehicle, when the warning is 'old fuel' how does one know which fuel is it referring to?

[otolith]

PositronicRay said:

On a dual fuel vehicle, when the warning is 'old fuel' how does one know which fuel is it referring to?

Are there any dual fuel hybrids?

[MikeB444]

You've not passed a significant birthday recently have you and forgotten to charge it?

Could actually be saying:

'Old fool, hybrid not available'

[Truckosaurus]

PositronicRay said:

On a dual fuel vehicle, when the warning is 'old fuel' how does one know which fuel is it referring to?

Oh noes, me electrons have gone off.