saffaclint79

Replaced knock sensor, now problems!?

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I replaced my knock sensor a couple days ago with the help of an auto sparky friend. It all went well but something just isn't right with the car now. It goes OK when you take off from a stand still and is OK on the open road but as soon as I bury the throttle **** goes haywire! It seems slow to boost and then when it should be on the second turbo it boosts like mad but then cuts out and gets all kind of jerky if that makes sense? I've done some research online and I've got a feeling a restrictor pill might have gone missing during the job? The question now is from where, how do I find out where they're meant to be fitted, where do I get the part/s? I've looked for pictures etc online but they confuse the living **** out of me as every one seems different.

Stupid cars!!!

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What model Legacy is it? Was the replacement sensor a new genuine one? Was the ECU reset afterwards? If the ECU was reset afterwards you could check for fault codes to see if the knock sensor CEL flashed up again since the swap.

Very highly unlikely a restrictor pill fell out. Could have been over tightened and cracked the new sensor, or an intake pipe clamp not fitted properly under the TMIC.

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It's a 2000 (BE5) Legacy Blitzen. I got the part from BNT but thinking back now that code wasn't cleared? Mate unplugged the battery, should have used his diagnostic tool in hindsight. As for the knock sensor being overtightened, we torqued it the recommended amount and put it back in at the right angle. I'm thinking I'm going to take the intercooler out and check all the hoses etc and see about getting the code cleared properly. Since the replacement the check engine light hasn't come on again and the car definitely isn't stuttering and under powered.

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Got to work early and decided to look at what we had done and see if anything was out of place. There was a hose that hadn't been clamped and was loose on its fitting so to speak. I removed the intercooler and looked for anything out of place where we had been working on the knock sensor but couldn't see anything. I put it all back together and took it for a drive, NO CHANGE! It's just not boosting right and when I put my foot flat the rec'd rise and you feel boost building but all if a sudden, around 4k the car just hits a wall and makes a horrible noise that makes you instantly back off. It's that bad that it feels like the whole driveline wants to lock up, it scares the **** out of me!!! Only option is to take it to a mechanic and see what's what.

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We didn't disconnect any vacuum lines when we removed the intercooler so I can't see how any of the lines would be in the wrong place etc? I'm sick of the ****ing car and want rid of it TBH. I might get another Subaru but more than likely a manual and definitely non turbo, maybe a 3.0 H6. Obviously this problem needs fixed but it's driving me to madness, it seems to be costing money every few weeks. New radiator, rocker cover gaskets, new inner CV boots, new power steering rack ends, new brake pads, new knock sensor, bulbs etc etc etc and I've not owned it 2 years yet.

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If there's no boost leaks anywhere, it could be unrelated and the AFM is now playing up.

Disconnecting the battery while doing the knock sensor would of reset the ECU, so you could check for fault codes manually to see if anything's come up. Read the section in here on manually reading codes:

http://www.scoobypedia.co.uk/index.php/Knowledge/ReadingECUCodes

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Well it might give you a pointer now, it's hard to say a car boosts slowly if you can't see the actual PSI level

Did this problem start happening -right after- you replaced the knock sensor, or is it an issue which has started to happen later on

The symptoms you're describing could be a couple of things and it's not a major issue

- A boost leak, whether an actual leak or the BOV sticking open (also if the secondary BOV is opening it'll do the same thing)

- Something in the sequential system has been fcked with, maybe the intercooler valve is stuck open (or not opening)? That'd have the same effect

- An intake leak - the non pressurised side, if it's sucking in unmetered air it'll do this

- Faulty AFM tends to behave like this sort of also

As dumb as it sounds, did the pipes bolted to the intercooler get unbolted? If so and they haven't resealed that could do it

Does it idle, can it drive around nicely, or is it running like poos 24/7

Also describe the noise, are we talking misfire etc or more an air rushing sound or what

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The car drives fine so long as I don't give it the beans and get the second turbo involved, lol. It idles fine and feels no different to how it did before that knock sensor started freaking out. There's no real noise but say I'm doing 80kph and plant it, the car revs, boosts like normal and then just when you expect it to lift its skirt and haul arse its like the most intense speed cut kicks in and the whole car kinda lurches and shudders. It's hard to describe but it's actually kinda scary.

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Very much seems AFM problem related OR a boost cut outright

AFM related can also mean air leaks in or out

I'd be looking into checking the various components work right, put it into test mode (plug in the green connector under the dash), and check that the intercooler valve is cycling open and closed, and the exhaust valve rod is also moving in and out. Might be as simple as a vacuum hose got snapped or torn when you had the intercooler off and on a couple times - also are you sure the hoses are clamped to the turbos tight - I've done it before where they feel tight as but I've accidentally hooked the hose clamp on top of the little locator bit and while you can't pull the hose off, air can slip out that joint

Could also be a spark issue, I doubt it, that normally feels like a misfire on boost as opposed to a hard cut if that makes sense

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I had the same thought about the hoses so I took everything off again and refitted the intercooler bring careful to make sure the hoses etc are tight. Took it for a drive, same problem!! I had a look in the foot well of the car and can't see the green and black plugs, do you need to be a midget Chinese contortionist to be able to get in there and find them?

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They'll be straight above where the clutch pedal should be. Could be taped up if they've never been used before:

classic_test_mode_connector.gif

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