Diagnosing Knock with Android Torque-Pro app
 

Hi Everyone,

I'm in the UK with a 2.5 non-turbo 2005 car.

I am having real problems with knocking/pinking in my car, especially when the weather is hot. Now the weather has cooled down a little it is better, but it is stil doing it at times.

I am getting it when I lift off the throttle, then goback on the throttle at low speeds, eg intown. 2000rpm/20mph in2nd gear (its a 4-speed auto) seem to be the trigger points.

I have teracleaned the car (removes carbon), replaced the knock sensor, changed the plugs, and cleaned the MAF sensor and beyond that am at my wits end to know where to go next.

Just bought the ANdroid Torque app and a bluetooth scanner but not really sure what I am looking for in the logs, or what to log.

I used to be a research scientist so used to looking at this kinda stuff, but really need somehwere to get started and focus on.

anyone help me with what to log (and how to log the knock sensor with this app - Ican't find the option)/

David

I'm not really going to be able to give any input with regards to the android thing but what grade of fuel are you using? Poor quality fuel will certainly create knock and seems to be the only thing you haven't mentioned as yet.

Not sure on the mechanical end , but do you have the TorquePro knock detector add-on for the app ? Go to the app store and go to Torque , and go to "other apps by this developer".

I have tried 97 super unleaded, but it even knocks on this in the hot weather, although with current weather I have tried going back to the 95 and it is not dong it very often now, but I can still hear it sometimes.

As far as I'm concerned a standard unmodded UK car should run on standard 95 Ron petrol - if it doesnt theres either a fault with the vehicle or the design isn't fit for purpose....

if it was an import or turbo'd I can understand the need for higher octane petrol but it is neither of these.

Will try the knock addd on for the app.

My UK turbo needs super unleaded according to the sticker inside the fuel cap cover but I don't know what the requirement is for non turbo.

I'd be thinking along the lines of a spark plug or maybe even a timing issue. Do you know what plugs are fitted currently?

Try tesco or shell 99 fuel. Its nothing to do with fit for purpose if it is a "performance car" and that's what the manufacturer specify then that's what is required.

My vectra vxr specifies 97 or 99 fuel and that is a uk model...

You are yet to confirm if the engine is running lean or not. It doesn't matter what grade fuel you run, even if its tuned for 95Ron it'll still pink on 99RON if its running lean.

Things to check:

Oxygen sensor switching and voltage. Is it giving lean or rich readings? Live ECU date is helpful here, if possible. Fuel trim values will give further clues.

If lean: Check for Air/vacuum leaks. A difficult task without a smoke testing machine.

Swap MAF with a identical new or a known working one off a healthy car. Not a second hand one one sold random dude off ebay, and it MUST be a Denso branded, not a copy/cone or other manufacturer. A failure mode of hot-wire/hot-film MAF sensors is to under-read the volume of air passing through them. Cheap clones and copies can suffer issues both of accuracy and longevity.

Other areas to consider:

I'm not sure, but does this era of n/a Impreza engine have any EGR (be its separate or induced via variable valve timing) or variable length intake/swirl flaps? If so then a fault with these can also have a impact on the way fuel burns.

Fuel pressure about 45psi IIRC :Also a leak down test after engine is switched off (it should hold fuel 45psi pressure for at least a few minutes after shut down). Low pressure and/or leak down, change regulator. If fault persists, check out the pump.

Fuel flow: Run pump from a 12v feed and check fuel flow from the fuel rail into a container and time how long it takes to get a litre of fuel, you should get at least 2 litres per minute, ideally more (although Subaru spec a minimum of 65litres per hour, in reality you should get more than this). Submerge the hose in the container whilst filling it to see if any air is in there too. Fuel aeration will cause problems: usually air leak in fuel pickup (this will typically vary on fuel level). Obviously take usual precautions when messing with the fuel system (don't feed fuel to the dog or test its flammability with a match etc yadda yadda). Low fuel flow; change fuel filter, if problem persists, look at the pump.

Hi

So if I log the O2 sensor output, what values should it be ?

How would I Know from the output if it is lean or rich ?? (how will it change from what to what ?)

And what should the fuel trim values be ......

Is there anywhere on the net where it gives values for these parameteers I can check against..

Thanks