Really bad fuel economy problem

[aceventura]

Just checking, are you driving a few hundred km to get these readings, do you do the maths when you fill up at the pump? It takes a fair bit of distance for in-car meters to read accurately. Even after a full tank mine is still often a litre or so off, and if I've only driven 10-20km it can be up to 10L off!

What exactly are you saying here?

In my experience the fuel consumption calculated by the trip computers is fairly reproducible - if the fuel consumption rate is higher than you expect, I think it is likely you are using more fuel than you expect. Driving 10-20 km from a cold start can use substantially more fuel than the next 20 km once the engine is hot. I am not what is happening in your circumstances, but I refuse to believe that the trip computer is that far out over small distances.

Regarding accuracy of the meters, it is just a matter of calibrating them. I calibrated mine and and if you cross check the amount of fuel added at the pump and what the trip computer thinks the car has used, the two numbers are within 100-200 mL everytime. This means that all the calculated fuel consumption rates are accurate to better than 1%.

My understanding is that the trip computer just counts injector pulses and converts that into the volume of fuel injected (using an appropriate calibration number). Hence, if the numbers still don't add up, I would guess you have a leaky or blocked injectors, or bad fuel pressure.

Please correct me if I am saying anything stupid

 

[EREXON]

Its been almost a quarter tank and it has settled to 20L/100KM.

thats with an average speed of just under 30KM is that normal for city driving???

 

[EREXON]

iv filled up with premium plus added a whole bottle of injector cleaner.

overall car runs alot smoother and better but i fuel is still being over consumed.

 

[danja]

What exactly are you saying here?

In my experience the fuel consumption calculated by the trip computers is fairly reproducible - if the fuel consumption rate is higher than you expect, I think it is likely you are using more fuel than you expect. Driving 10-20 km from a cold start can use substantially more fuel than the next 20 km once the engine is hot. I am not what is happening in your circumstances, but I refuse to believe that the trip computer is that far out over small distances.

Regarding accuracy of the meters, it is just a matter of calibrating them. I calibrated mine and and if you cross check the amount of fuel added at the pump and what the trip computer thinks the car has used, the two numbers are within 100-200 mL everytime. This means that all the calculated fuel consumption rates are accurate to better than 1%.

My understanding is that the trip computer just counts injector pulses and converts that into the volume of fuel injected (using an appropriate calibration number). Hence, if the numbers still don't add up, I would guess you have a leaky or blocked injectors, or bad fuel pressure.

Please correct me if I am saying anything stupid

I'm saying that often when I reset the trip meter after filling up it will read quite high for a few kms before it settles down into what I'd call a "proper" reading. It may well be accurate for the actual kms driven, but won't be indicative of actual consumption over an average tank.

I put it mainly down to stop/start traffic, as you just reset the meter then pull out of the servo, pull up to a traffic light and sit there using small amounts of fuel to go nowhere, which because the computer doesn't have enough sample data, really skews readings until you've driven a bit to give it more data to average it out.

So basically, yes it probably is fairly accurate for what you've driven since you reset, but until you've driven a bit the number won't be truly indicative of what your average consumption is - does that make sense?

I find when I do the numbers myself when I refill, the trip meter is about 0.5-1L above actual usage, yes so pretty close.

 

[aceventura]

It may well be accurate for the actual kms driven, but won't be indicative of actual consumption over an average tank.

I agree absolutely - I just didn't interpret your previous comments correctly. Sorry about that

Its been almost a quarter tank and it has settled to 20L/100KM.

thats with an average speed of just under 30KM is that normal for city driving???

There is city driving and then there is city driving.

Driving around Sydney outer suburbs I average around 40km/h - There is a lot of stop start, but then there are plenty of 70 km/h zones too. This sort of driving I get ~12-13L/100km.

On a recent trip to Brisbane from Sydney I averaged around 8.3L/100km on the freeway (avg. speed 90km/h). I reset the trip computer when I filled up in the city in Brisbane and I was doing 18L/100km (avg. speed ~25km/h) driving around the inner suburbs. I also used about a quarter of a tank.

I consider that my car does fairly well on fuel, but it all depends on the exact conditions. I think you really need to get your car on the open road - if you don't hammer it too hard and you can get to below ~9.5 L/100km I think your car is normal.

 

[danja]

I agree absolutely - I just didn't interpret your previous comments correctly. Sorry about that

No probs mate, I should have been more specific


@OP: If you had a V8 those numbers wouldn't be too out there, but my V6 used to get 12-14L/100 in the average week, and that was doing a 50km round trip to work each day, just outside of the city, taking Victoria Rd which averages like 25km/hr :bang:

Did you have a look at your plugs?

 

[EREXON]

I think the car might be fine at the moment. Its driven only locally at the moment as im on uni break so i aint doing too many kms on her.

The average speed is approx 28-30km/hr and its on 20L/100KM.

So im thinking when it gets up to an average of 40km/hr + it should go at least 17-18L or less.

Thats no highway driving at the moment and only short trips.

There was a fuel problem as it was sitting on 25L lowest ever was 18L. With the things ive done/changed at the moment its a constant 20L and thats stop start.

So i will see how it goes on a longer trip.

Im not driving granny style nor hoon but just normal cruising without over revving.

Will see how it goes on a nice drive and will report back.

 

[EREXON]

I havent looked at the plugs yet but i will in the next few days.

 

[EREXON]

Hi just wanted to tell you all that since the bad fuel economy days i have since changed 02 sensors, flushed radiator, changed spark plugs, ran a whole bottle of injector cleaner through the fuel tank and cut the pink wire.
will do leads soon.

and now from 25L/100KM.

its on its second tank of petrol and has dropped dramatically down to 16L/100KM and still dropping.

My driving styles havent changed that much i still drive normal not like a granny. just keep the car flowing.

I recommend doing the 02 sensor change, plugs, leads and injector cleaner. it made the car run smooth as.

If anyones car is missing or running a little lumpy i highly recommend you do all the above it has made a huge difference to the car and the fuel economy has become alot better.
If anything changes i will let you guys know but so far so good.