Worse Fuel Consumption After Ecu Reset

[kev dood]

My Battery was changed in my car a week or two ago. As this will reset the ECU, I have been driving around a little more concervatively (always use Optimax so was already in tank).

Basically I have so far done a 1/4 tank of fuel and so far the petrol consumption is about 1/3 more than before. I usually get about 90-100 miles out of a quarter, but currently got 60-65!!

Is this normal, and will it get better? I shall not be happy if the consumption stays this bad as I used to average about 27 mpg through whole of tank before hand (which was bad enough).

Was expecting it to be better!!

On the plus side, the car is more responsive and has a little more poke (mainly once the revs pick up a little, 2.5K+!!)

[ColinBarber]

It should get better. It can take a while for the fuel trims to sort themselves out.

[GXE10]

yep..... same with my car.... usually it will take 1-2 full tank for the fuel consumption to come down.......

so..... don't reset the ECU all the time

[RoadRash]

Interesting topic!

There I also have a question.

Would I notice any improvement with intake and exhaust when I would reset the ECU?

Or would I also have to reset it when I change from 95octane fuel to 98octane fuel?

Anybody knows??

[Zee007]

You should reset the ecu if you change fuel types or have the intake/exhaust fitted.....

[Kremmen]

Interesting point there.

My journey to work takes in a dual carriageway for about 3 miles, then motorways for 12 miles, then a 50mph A road for 6 miles. I suffer no holds ups at the times I use.

As a result my MPG has always been 5-7 above what the manufacturers claim for their combined figure.

I have only measured one week of MPG to date but it came in at 30MPG which is only 1 above the quoted figure.

Do I understand that this figure will improve as the ECU adjusts ?

[ColinBarber]

The ECU has a pre-programmed fuel map that it uses to inject the correct amount of fuel. However the O2 sensors in the exhaust feedback how rich/lean the engine is running and the ECU then adjusts the short term fuel trim to correct. There is also a long term fuel trim which is adjusted but at a slower rate. Resetting the ECU erases the fuel trims and that is why MPG alters. I guess the standard map slightly over fuels to protect the engine which is why people see a reduction in mpg.

You may see an improvement due to the ECU adjusting but also you should see an improvement as your engine runs in.

[Kremmen]

Thanks - I was not aware :)

[kev dood]

ahhh, think I can breath easier now then! Was starting to get really alarmed as I couldn't drink it any quicker!! (guess thats a poor example!!)

[Hawk Man]

After reading the fuel test that I think Fidgits did, I changed to Shell Optimax. It took about 4 tankfulls to see a change but I went from getting about 280-300 miles/tank to 360-380 miles per tank. This is on a regular journey to work, 45 miles of which about 30 are on the M25. I never reset my ECU

[RoadRash]

After reading the fuel test that I think Fidgits did, I changed to Shell Optimax. It took about 4 tankfulls to see a change but I went from getting about 280-300 miles/tank to 360-380 miles per tank. This is on a regular journey to work, 45 miles of which about 30 are on the M25. I never reset my ECU

You didn't reset?

The result was that you needed 4 fuel tanks until it worked.

If you would reset it, it changes the values quicker as far as I know.

====================================================

I heard that if you would add a turbo charger the stock ECU would also increase fuel to adjust the mixture.

BUT: The ECU doesn't know what's happening suddenly when the turbo is spooling up.

There is so much air in the engine, but the oxygen mixture at the lambda is OK at this time.

So it doesn't increase fuel immediately, but just when the increased air reaches the lambda then the ECU will increase fuel.

BUT: While the turbo is spooling up and pumping a*s-loads of air into the engine the fuel is too less and so the mixture is very, very lean so that it burns much too HOT and it can damage engine, O2 sensor and catalytic converter.

If you would drive at 4800rpm for some while the ECU would increase the fuel until the mixture is OK, but just after some time.

Fact: The biggest problem is while accelerating, the ECU doesn't know that it should suddenly give so much more fuel, and the mixture while spooling up is far too lean and causes much too hot burning progress.

Meaning: the stock ECU is too slow to react, in cause of the stock settings.

[RoadRash]

Dam*!

I filled my tank full with 98oct. fuel some time ago for about 4 tanks.... fuel prices increased and now I changed to 95 back.

Result: My IS200 now needs the 1/4 tank for 100km.

Those are 400km a tank..... (~250miles a tank)

Dam* :tsktsk:

If I do an ECU reset.... what will be the effect in the first few kms or 100kms.... don't know???