Jamie.Smith

Can anyone confirm or deny would a 94MY UK turbo have a maf sensor and knock control?

I am looking at changing my down pipe and have beem tood that if I have these two items I will have no problems.

Jamie

Jan Shim

Jamie,

The earliest model Subaru WRX i have experience with is a '95 and it has a Knock sensor and Mass Air Flow. What has changing downpipes got to do with Knock and MAF ??!!

Jan

Jamie.Smith

Someone suggested to me that if I changed the down pipe it would alter the air fuel mixture. So to ensure no damage to the engine I would need to get the ecu reprogammed or if it had a maf sensor and knock control I would be ok as it would be done automatically.

Jamie

Simon

Jamie,

All Impreza Turbos are fitted with MAF and knock sensors. On detecting knock, the ECU can retard the ignition, but only to a certain degree.

Fitting of a downpipe allows the car to breathe more easily, so does alter the mixture. On STIs, that can run on the edge of knock anyway due to our poor quality fuel, this can be a problem. On a UK car, you should have no problem fitting a downpipe, many other owners have done so.

Simon

Jamie.Smith

Thanks Guys

Jamie

Jan Shim

Jamie,

The factory downpipe is very restrictive to flow due to the catalytic converter. Once you replace this with a free flow d/pipe, this restriction is removed to the point the turbo is now able to spin more freely (you can hear the turbo "whistle" as it spools). This also means it can "pump" in more air and if not corrected, the end result is a lean A/F mixture (more air to fuel ratio).

Unlike other Japanese performance vehicles, the Subaru WRX employs a self learning control system. The "air fuel ratio learning control system constantly memorizes the amount of correction required in relation to basic amount of fuel to be injected (the basic amount of fuel injected is determined after several cycles of fuel injection)..." [1997 Workshop manual].

This is handy too when you start to experiment with less restrictive air filters hence the self adjusting ECU is useful. Unfortunately on '99 and later models, the use of MAF Hot Film sensor tends to incriminate aftermarket filters as the cause of contamination.

It is my understanding that Australian WRX run very rich fuel mixtures from the factory. I would expect this to be the same (in fact more so) when good octane fuel is generally not available. Essentially the higher the octane, the higher the resistance to knock. Where i am (Brunei), I have the luxury of 97RON and very cheap fuel (0.53 cents/litre) so fuel consumption is hardly something we give a second thought to.

The factory JECS ecu retards up to 5º on detecting knock. I can only assume that the retard isnt incremental (unlike the Link ecu where retard can be a little as 1º) because you can feel significant power loss (sluggish feel) when retard has occured.