99' Leganza 2.2L Pre-Ignition?

[teteous1]

My 1999 Leganza has developed a strange noise. It has 96,500 km's.
When I am driving along and when the engine reaches just over 1,500 RPM, but below 2,000 RPM a metallic tapping/knocking noise sounding like a rattle appears - if I rev harder through it, it goes away (Over 2,000 RPM). When the engine changes down (it's an auto) there is no noise and as long as I am accelerating or have foot off pedal (so slowing down) there is no noise. It is only if I'm over 1,500 and below 2,000 RPM and cruising along on a constant throttle that you can hear this sound. I am under the impression it is pre-ignition, but am currently unsure how to rectify the situation.

I have been putting an injector cleaner into the fuel for the last 2 tanks of fuel and no improvements have been made. I have also been using premium 98 octane fuel for the last 4 full tanks as i thought it might have been a lean fuel/air ratio.. I have also changed the Spark Plugs, when i changed them, the first run was nice and no rattle was heard but progressively came back to haunt me to the point I think it is worse than it previously was.

There seems to be nothing else wrong with the car and I have been maintaining it quite well, hoping someone might have an idea what it may be as i'm out of ideas.. Maybe a faulty knock sensor (I understand they dont work under 2,000 RPM???)

Thanks for reading.


Regards,
Teteous.

[benzino]

every auto i've been in does this under load... like cruising up a hill with 1/2 throttle
just kick it down if it's bothering you

[Big Jeff]

every auto i've been in does this under load... like cruising up a hill with 1/2 throttle
just kick it down if it's bothering you

yep my dad auto audi does the same thing when drininh from a stand still and under load

[teteous1]

Alright, thats good to know..

I just thought it might be damaging to the engine, glad its all good.

Thanks.

[benzino]

yeah it's just an auto thing as far as i know

my mum's had 3 auto legacy's and they've all done it

[teteous1]

Fair enough.. Still annoying though..

I figured i'd just continue here and make a new topic as it is kind-of related.

My Woo has now developed a 'loose-rattle' when i turn it off, sounds like its from the front right of the car, but it only happens after the car is warmed up so like a 10min drive and it will do it..

I tried to record it, but its a lot more faint than I can hear it in the clip.

But anyways here is the clip

Rattle.zip

Woo rattle

(69.7 KiB) Downloaded 112 times

Any suggestions would be appreciated.

Teteous.

[PrecisionBoost]

I have also changed the Spark Plugs, when i changed them, the first run was nice and no rattle was heard but progressively came back to haunt me to the point I think it is worse than it previously was.

There seems to be nothing else wrong with the car and I have been maintaining it quite well, hoping someone might have an idea what it may be as i'm out of ideas.. Maybe a faulty knock sensor (I understand they dont work under 2,000 RPM???)

What color were the old plugs?

If they were all nice chocolate brown your car is running well, if one or more are white with pitting then it's lean.

With pre-ignition it will definitely show up in the plugs.

Have you changed your timing belt and timing belt tensioner????

At the number of km your at you should have done it already, if not do it ASAP.

The tensioner can make noises like you mention just before it fails, some people concentrate on the belt but forget the tensioner which is just as important.

The most likely time for pre-ignition is during hard acceleration as opposed to light throttle cruising so it's certainly not the first thing that came to mind when you mentioned the noise.

Other culprits may be the exhaust system resonating or rattling at just the right RPM

[teteous1]

Three plugs were as you described 'chocolate brown' with one a bit oily, but not too bad.

I changed the Timing belt and tensioners at around 85,000km as a squealing was coming from that area of the engine, i thought it was the Serpentine belt, so i replaced that, but it ended up being a frozen Timing belt tensioner.

So the timing belt + 2 tensioners have been replaced.

How would I go about testing to see if it is the exhaust system resonating?

[teteous1]

Putting 98 octane fuel in seems to reduce the knock somewhat, but its there still.

Any suggestions?

[Trackerrrr]

Check the exhaust heat shield, it may be loose also.

[teteous1]

Checked the exhaust sheild, and it is tight.

I think it may be coming from the Serpentine belt tensioner as it vibrates a lot when im looking at it, and its coming from that area.

Another thing with the rattle is, if i turn air-con on, it will rattle loud then subside, and when i turn it off it does the same, thats what made me think it has something to do with the belts.

A new tensioner is around AU$60.00 + postage, and i just ordered a new waterpump so ill have a look at it when i replace that.

[Trackerrrr]

Just an update, check your muffler at the rear of your car. My Leganza developed a very annoying loud rattle just off idle that sounded like a loose heat shield. Turns out it was the rear muffler, the baffles inside have come loose from rust. I had to shake the muffler to find the rattle, but it's definately coming from there.

[teteous1]

Ok thanks, will have a look, was a new muffler less than a year ago, but will check it no the less.

Thanks.

[teteous1]

turns out, I shook the muffler and the rattle was coming from the catalytic converter. Half of the inside had came loose and thats what was causing the rattle.

Thanks for everyones help