Re Setting ECU

I had the cam belt changed on our Forester XT ( Turbo ) just over a year ago. Afterward we noticed a increase in performance and a decrease in fuel use! I talked to the guys that did the job and they thought that as the battery was not connected for 48 hours that the ECU would have been re set! It has just been in for a service etc but back to the lower performance pre cam belt. Should I disconnect the battery for say 24 hours again to "re set" the ECU!

I was told to disconnect my battery plus turn the light switch on to drain any non main battery voltage from the system and then when I reconnect my battery the ECU will power up with the factory settings it had from brand new.

nadoubtthat would ,only work on some older mitsubisheaps .
a foresetr is probably obd 2 if its not your probably cross 2 diagnostic cables to whipe the ecu clear the fan will start spinning up and stop spin again on and off indicating its reset the ecu and whiped the error codes.

its more like a oxigen-lambdasensor not working right if fuelconsumption goes up.

Hmmm. I guess this makes sense to someone.Intrade, can you reword somehow please as this is a common situation with other cars too.

you want to check the exhaust emission with a gas analyzer that would soon tell you if there is a problem.and explore forums like this or take it to a subaru expert with special subaru diagnostic tools dont know what that would be
i just got volkswagen professional tool.
http://www.subaruforester.org/vbulletin/f66/how-check-o2-sensor-41523/ http://www.troublecodes.net/Subaru/

This is a common problem for some cars dont know if it is but the
oxigen sensore mesures the exhaust gas and tells the ecu=engine computer its findings , if its faulty the computer can think it must inject more fuel and starts using loads. there usually is 2 sensores and the problem is mostly on petrol with catalisator and thats almost all cars now , even my 1985 carina has had a oxigen sensor and acat. But no ecu so did not matter as mutch when it stopped.

another problem is faulty temperatur sensors. most cars throw a check engine light some new onescan even check the lambda -oxigen sensore. like our new 2011 dacia sandero does its own emission testing and throws a warning light if something fails. Other new cars would probably do similar older cars wont throw a , c-e-l if the oxi dies or is not reading correct.

Dingo, what the mechanics were describing is the fact that the computers adapt the mixtures and the ignition timing to allow for wear in the motor, blocked exhausts, heavy loads or driver behaviour even.
They come with a set of figures, these figures tell them how much fuel to inject at every throttle, rev, temperature etc condition. They use the default settings then as they detect that the mixture is a bit rich say, or too lean, they move all the figures up or down a little. They do this over the course of each drive, this is called short term adjustment.If the computer detects that it's always having to add a bit, it moves the original set of figures up by a few notches and sets it there in a more permanent way, called long term adjustment. this process is built into all ecus nd has been from the earliest days right up till now.
Once it's adjusted the long term adjustment, the car will always run that bit richer say, which will be to compensate for some thng like a partially blocked, until it has had several drives where it has found it's too rich, then, it will have performed the short term adjustment several times and will decide to bring the long term adjustment down again.
Disconnecting the battery resets the long term adjustment. the car goes back to original settings, till you go for a drive, when it will carry out short term adjustments, then after a few trips, it will perform the long term adjustments needed. These adjustments are because fuel varies, temp sensors get out of whack slightly, driver behaviour varies, wear happens, air cleaners and exhausts get partially blocked.

The changes that happened after the battery disconnect, should have all been negated after a few drives.

So, now you need to try and figure out what is happening to the car. The simplest thing is to get someone to attach either a scan tool or a computer to the car and have a look for trouble codes, which indicate faulty components or wiring, or out of range settings, that is the allowed adjustments are not being enough to remedy the problem even after all the long term and short term adjustments have been done. or, even better, take the car for a drive with the test tool or computer attached and record all the settings, fuel, timing , temp etc, as you drive. that is the way to diagnose the problem.

First though, before you do that, you should do a standard tune up, check all the small rubber pipes are attached and not perished, check the fuel type is suitable, check tyre pressures, and perhaps, make sure you have not just got used to the car and aren't perhaps taking it's performance for granted.

Dingo, what the mechanics were describing is the fact that the computers adapt the mixtures and the ignition timing to allow for wear in the motor, blocked exhausts, heavy loads or driver behaviour even.
They come with a set of figures, these figures tell them how much fuel to inject, what to set the timing to,at every throttle, rev, temperature etc condition. They use the default settings, then, as they detect that the mixture is a bit rich say, or too lean, they move all the figures up or down a little. They do this over the course of each drive and this is called short term adjustment.If the computer detects that it's always having to add a bit of short tem adjustment, it moves the original set of figures up by a few notches and sets it there in a more permanent way, called long term adjustment. this process is built into all ecus and has been from the earliest days right up till now.
Once it's adjusted the long term adjustment, the car will always run that bit richer say, which will be to compensate for some thing like a partially blocked exhaust, until it has had several drives where it has found it's too rich, then, it will have performed the short term adjustment several times and will decide to bring the long term adjustment down again.
Disconnecting the battery resets the long term adjustment. the car goes back to original settings, till you go for a drive, when it will carry out short term adjustments, then after a few trips, it will perform the long term adjustments needed. These adjustments are because fuel varies, temp sensors get out of whack slightly, driver behaviour varies, wear happens, air cleaners and exhausts get partially blocked.

The changes that happened after the battery disconnect, should have all been negated after a few drives.

So, now you need to try and figure out what is happening to the car. The simplest thing is to get someone to attach either a scan tool or a computer to the car and have a look for trouble codes, which indicate faulty components or wiring, or out of range settings, that is the allowed adjustments are not being enough to remedy the problem even after all the long term and short term adjustments have been done. or, even better, take the car for a drive with the test tool or computer attached and record all the settings, fuel, timing , temp etc, as you drive. that is the way to diagnose the problem.

First though, before you do that, you should do a standard tune up, check all the small rubber pipes are attached and not perished, check the fuel type is suitable, check tyre pressures, and perhaps, make sure you have not just got used to the car and aren't perhaps taking it's performance for granted.

what a magnificent explanation mechnificent.even I can understand it.

Ha.thanks.

mechnificent, that must be the most informed and logical explanation I have ever seen on this message board! I will follow your advise and book it in for a proper diagnoses at Subaru, thanks for your help

I would hazard a guess that the air filter and spark plugs were replaced when the cam belt was done. and now it's time for them to be replaced again.

mechnificent wrote:
Dingo, what the mechanics were describing is the fact that the computers adapt the mixtures and the ignition timing to allow for wear in the motor, blocked exhausts, heavy loads or driver behaviour even.
They come with a set of figures, these figures tell them how much fuel to inject, what to set the timing to,at every throttle, rev, temperature etc condition. They use the default settings, then, as they detect that the mixture is a bit rich say, or too lean, they move all the figures up or down a little. They do this over the course of each drive and this is called short term adjustment.If the computer detects that it's always having to add a bit of short tem adjustment, it moves the original set of figures up by a few notches and sets it there in a more permanent way, called long term adjustment. this process is built into all ecus and has been from the earliest days right up till now.
Once it's adjusted the long term adjustment, the car will always run that bit richer say, which will be to compensate for some thing like a partially blocked exhaust, until it has had several drives where it has found it's too rich, then, it will have performed the short term adjustment several times and will decide to bring the long term adjustment down again.
Disconnecting the battery resets the long term adjustment. the car goes back to original settings, till you go for a drive, when it will carry out short term adjustments, then after a few trips, it will perform the long term adjustments needed. These adjustments are because fuel varies, temp sensors get out of whack slightly, driver behaviour varies, wear happens, air cleaners and exhausts get partially blocked.

The changes that happened after the battery disconnect, should have all been negated after a few drives.

So, now you need to try and figure out what is happening to the car. The simplest thing is to get someone to attach either a scan tool or a computer to the car and have a look for trouble codes, which indicate faulty components or wiring, or out of range settings, that is the allowed adjustments are not being enough to remedy the problem even after all the long term and short term adjustments have been done. or, even better, take the car for a drive with the test tool or computer attached and record all the settings, fuel, timing , temp etc, as you drive. that is the way to diagnose the problem.

First though, before you do that, you should do a standard tune up, check all the small rubber pipes are attached and not perished, check the fuel type is suitable, check tyre pressures, and perhaps, make sure you have not just got used to the car and aren't perhaps taking it's performance for granted.[/quote

The only thing you could add to that, istoemphasize how beneficial it would be to trade it on a Golf or an A3

(sorry Jazz)

Thanks.

It might be interesting to see what disconnecting the battery does. make sure you know how to get the radio going after though. Probably best though to only do that after subaru have had a look at it.

I have a subaru, well two actually, and the older one though it goes fine, I know it's getting up in the miles, and not quite got full compression. Because I only use it for a spare when my boys or a customer or someone need to borrow it, I take the battery terminal off when it's not getting used. It always runs better when I first get it going and for the first trip, then it starts getting symptoms like starting up a bit raggedly, and being a but sluggish till it warms up. It's because the adjustments are getting adjusted right to their limits I suspect. soon I'll have to stick some rings and bearings in it to get it running sweet again. cept I'm a mechanic and probably wont.haha.

You could get the subaru guys to get the trouble codes, and then record what we call "live data", and possibly give you a copy of the readings. which we could look at here if they don't notice anything unusual.
If they don't find anything too far outside the normal readings, I'd suspect the engine could be worn, the valves might need adjusting, the exhaust/catalytic converter could be blocked. some sort of mechanical fault rather than a tune or electrical problem.

Modern cars are tricky to diagnose. There will be plenty in here that will take guesses at common problems like air flow meter, O2 sensor, temp sensor etc. but those parts cost hundreds each, and some of them will give false readings, or even set trouble codes indicating that they MIGHT be faulty, when really they are only reading a figure that is out of range because of some other problem. So the O2 sensor could seem to be faulty, when it's really a blocked air cleaner, or a miss-fire.

Get the dealer to check it over for you and hopefully record the live data, then if that doesn't cure or find the problem, try taking the battery lead off. if it goes right after the battery has been disconnected, I'll bet it's some mechanical problem. like the valves need adjusting or the motor is just getting a bit old. .

The ECU will be retarding the ignition timing. (via the process that mechnificent explains). Most likely caused by too much combustion gases getting past the rings. If you want to confirm this you will need a means of viewing live engine data. One of the fields will be amount of ignition retard applied to base maps. The cheap and nasty way to fix is to remove the PCV system then do the ECU reset. No more blowby gases with their oil mist entering the intake means the ECU thinks the engine is new again and no more retarded ignition.