tronlc

Just collected my car from the garage, they tell me the knocklink is knackered (standard), and this is causing the performance of the car to be "flat".

Is this true?

What would be the cost of the part and how long should it take to fit?

I am just curious as im not too sure about such devices!

Cheers

Graz

I suspect you mean the knock sensor.

KnockLink is a device made by Link to monitor your engine for detonation. Believe it or not they're not fitted to Impreza's as standard, neither do they have any effect on the operation of you engine.

A new knock sensor would be around £60-£80 I suspect, shouldn't take more than an hour or so to fit, not sure where the Subaru knock sensor is located, only know where to fit one for a KnockLink.

As to it causing "flat" performance, not sure about that, it would be looking for spikes to indicate knock and then retard the ignition accordingly. This would cause a loss of performance but I would of thought if the sensor wasn't working then you wouldn't get any spikes, the ECU wouldn't think there is any knock, and no retardation would take place.

Far more likely to be MAF or Lambda sensor related. Ask them how they reached this conclusion about the knock sensor. The only real way would be to correlate knock heard with det cans against the output of the sensor, either read through the select monitor port or displayed on an oscillascope.

tronlc

Yes thats it Knock Sensor.. They said it would be around £150 for the part and 2 hours to fit... I thought it a little expensive.

I took my car there just to see how it is running and thats the report they gave me.

What should I do? Is there anyway I myself can check the MAF etc?

Thanks

Graz

Helps if you give the model year. IIRC pre 98 cars have a different MAF sensor to the newer models. You'll find plenty of info through the search facility on MAF sensors, those fitted to MY99-00 are notoriously flaky.

The common giveaway for a failing MAF is unstable idling, i.e. the revs won't settle and swing between a few hundred to say 1500 when the car is warmed up. However the ECU can learn around a failing sensor so you won't always see it.

So the best technique is to wipe the ECUs memory by disconnecting the battery for a few hours, then start it up and see if the revs are swinging about.

Other indications include disconnecting it with the engine running, if it stalls MAF is possibly okay, if it doesn't probably duff. Also try reving to a constant RPM of say 4k, hold it for a few secs then take your foot off the accelerator. If the revs drop to nearly stalling before coming back up to idle then again the MAF is probably duff.

tronlc

Sorry, it is a 94 WRX. the idling is fine, doesnt fluctuate at all at idle. The battery was disconnected for a week or so a month ago so I guess the ECU had reset (didnt know thats how its reset!!).


From what you say I guess the MAF is ok, so it could be the Lambda sensor?

I am guessing here, and the guy said it in the garage, that the knock sensor would cause the engine to retard, I can see some logic in this if the sensor is for example giving a "knock" reading.

I Just checked and the Knock Sensor is £82+vat, and I beleive it is located behind the Alternator (maybe wrong tho!)

Thanks again.

Graz

Okay, MAFs on that year are much more reliable, but also expensive to replace as it is built into the induction system. The whole airbox has to be changed. It may be worth another ECU reset as these things can go all of a sudden.

Kind of reaching the limit of my knowledge here so hopefully one of the experts on here can help.

As it's a Jap import are you running it on Optimax + octane booster? If not the you may actually be getting a fair bit of knock, and hence the retardation. The Jap cars are mapped for the 100 RON fuel they get, Optimax is about 98 RON. Low octane fuel = knock = blown engine.

Regarding the Lambda sensor you can look at the output using a voltmeter, should swing around at idle and off boost, think it's between 0 and 1v, low voltage = lean, high = rich, on boost should settle on a high voltage (above 0.9V is ringing bells) to indicate a rich mixture. Again have a search on this site, should be able to find what the exact voltages are.

tronlc

Graz, your a star! Thanks for all your help.

I am running Optimax + NF booster as per posts on here, I will get the meter out in a few days and check the reading, and I will disconnect the battery tonight and reset the ECU again and check.

I am getting intermittently the Engine Check light on the dash when I start the car, and it can stay lit for a few seconds to a few mins of driving, so I guess the Knock Sensor is giving this fault.

Cheers

Graz

Ahh, didn't say anything about the check light coming on. There's a way to put the ECU into a diagnostic mode, I remember reading something about green and black connectors under the steering column Anyway if you do that the check light will flash out a code indicating the type of fault. If it is the knock sensor then obviously it's worth changing it though I may be a good idea to check the wiring first and continuity back to the ECU.

Anyway I'd better get on with my day job

Good luck

vindaloo

With a car that age that's been standing it's worth checking the wiring first to make sure all the connections are sound.

ISTR that MAFs on early cars car be cleaned with carb cleaner spray or similar as they're a 'hot wire' type of MAF. Suggest you find a reasonably technical thread discussing the merits of this before you start pulling it to bits though.

J.

tronlc

Just did the ECU check and it came back with 2 fault codes...


1. code 22, the Knock Sensor.
2. code 24, the Idle air control solenoid

Can someone tell me what could be the problem with the Idle air control solenoid, and is it something that is fixable!

Cheers all.

Brit_in_Japan

If you're getting fault code 22 then odds on the knock sensor will need changing (possibly could be bad connection between sensor and ECU, but most likely a new knock sensor required).

This would make the performance "flat" because the OBD (On Board Diagnostics) knows it cannot trust the knock sensor to detect knock and so for safety retards the ignition, hence less performance.

Sorry, can't help you on your other question.

Turbo_Steve

Idle solenoid sometimes just needs a good clean. If this doesn't fix it, it's going to need to be replaced.

tronlc

Cheers for all your help guys, I will try cleaning the the idle solenoid (I guess as it seems adjustable via the 2 screws (it is the beige thing with ABC on it??) I need to be precise when replacing?

Also the Knock Sensor is the thing with one wire going to it, as I look into the engine from the front of the car, just behind the alternator, behind the EJ20 engine stamp? Does it need to be torqued upto a specific setting when replaced?

Cheers.