Author Topic: The mysterious knock that got through the MOT last year  (Read 797 times)

Steve McF

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The mysterious knock that got through the MOT last year
« on: 17 July 2019, 08:14:29 PM »
I've mentioned this before on here, but my 2006 9-3ss B207 2.0T Aero has a knock from the front right side of the car when going over speed ramps. I get a similar knock when I start the car - like a single thud or thump as the engine fires up.

I had the car in with WMSS for chains a few months back and asked them to check this too. They couldn't find anything wrong - even the damper top mounts were OK.

The year before I bought the car, previous owner replaced the droplinks and anti roll bar bushes for MOT. I think he'd done coil springs too.

So could this be a knackered engine mount, or perhaps the exhaust downpipe hitting something? How many engine mounts are there on the driver's side if the car? There is the one you can see by the suspension turret, but is there another at the back of the engine at the bottom onto the subframe?

The car is in for MOT next week, so I have my fingers crossed. But if I have some idea, I can point my mechanic (who isn't very enthusiastic about Saabs anyway!!) to where the issue might be!!!
« Last Edit: 17 July 2019, 08:26:01 PM by Steve McF »

carrera

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Re: The mysterious knock that got through the MOT last year
« Reply #1 on: 17 July 2019, 11:04:53 PM »
Based on other vehicles, there's a good chance it is the exhaust banging, maybe a rubber mount or metal bracket is missing.

Engine mounts are another possibility. 9-3 I don't know but 9-5 has three, left hand side with the cradle, right hand gearbox and rear centre from gearbox to subframe.
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Steve McF

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Re: The mysterious knock that got through the MOT last year
« Reply #2 on: 14 August 2019, 09:29:48 PM »
Well the car got through the MOT again this year, with no reference to the knocking. So with everyone suggesting front suspension top mounts, or anti roll bar bushes, but with WMSS having found nothing wrong with these earlier in the year, I asked on the Facebook Saab 9-3 group whether it might be engine mount related.

One guy suggested up open the bonnet and get someone to start the engine and rev it up. If the engine kicked backwards significantly, then it could be the bottom mount on the rear of the subframe could be at fault, but that if it was, it was a cheap part and an easy job to change.

So this evening, I allowed the missus to sit in the driver's seat of Jet for the first time ever, with the key in her hand (dangerous, I know, but I gave her the benefit if the doubt  :P ;D ). I got her to start the car and then rev it up a few times. Surprisingly the engine did not really kick back, but I think I may have spotted what the issue may be.....

As she started the car, the whole air filter box, and the pipe back to the back of the engine shook. I thought, that didn't look right. On closer inspection, the air filter box appears to have no securing fixing at the front, and seems to be resting on the engine mount housing. Looking underneath, it is also not connected to the dirty side intake pipe that disappears down into the wheelarch area. The result is that the air filter box is rattling around held on by two fixings at the back, but not secured anywhere else!!

At the front down above the longitudinal, there appears to be some sort of rubber mount, that could form part of a fixing for the air filter box, but there is nothing in it, and certainly nothing extending from the filter box that could be part of a mount. So the question is, do I need a new air filter box?

The photos in the Haynes manual are very poor, and I can't see what the box is supposed to look like, even less how it is supposed to be installed.

I'll try and post some pics/video, if they are not too big....
« Last Edit: 15 August 2019, 06:27:00 AM by Steve McF »

Steve McF

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Re: The mysterious knock that got through the MOT last year
« Reply #3 on: 14 August 2019, 10:05:27 PM »
Can't upload the video of me waggling the box as the file is too big...  :o

Audax

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Re: The mysterious knock that got through the MOT last year
« Reply #4 on: 14 August 2019, 10:24:51 PM »
Can't upload the video of me waggling the box as the file is too big...  :o

Stop bragging and please don't upload that kind of video here, it would probably cause some Saab owners to have a fatal reaction....

Steve McF

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Re: The mysterious knock that got through the MOT last year
« Reply #5 on: 15 August 2019, 05:56:04 AM »
Sorry.....will keep it to myself....it was rather good though :D

If you are on the Saab 9-3 Facebook group, you can still see it here:

https://m.facebook.com/groups/1036015263075481?view=permalink&id=2702683333075324&comment_id=2705164082827249&notif_t=group_comment&notif_id=1565817614664025&ref=m_notif

Steve McF

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Re: The mysterious knock that got through the MOT last year
« Reply #6 on: 15 August 2019, 09:13:55 AM »
Just found an image of a B207 air filter box off Ebay, and it appears to have a bottom mount at the front of the box, which would make sense...although my filter box does not have it....  :o

smurkenstein

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Re: The mysterious knock that got through the MOT last year
« Reply #7 on: 16 August 2019, 07:32:25 AM »
Well the car got through the MOT again this year, with no reference to the knocking. Looking underneath, it is also not connected to the dirty side intake pipe that disappears down into the wheelarch area.

That sounds like part of the the secondary air intake- iirc, this system was omitted after about 2004. If you have the pipe going down the front, you probably have the system. That pipe should just push on. Later air boxes probably have this blanked off.

carrera

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Re: The mysterious knock that got through the MOT last year
« Reply #8 on: 16 August 2019, 08:50:58 AM »
Time for some field engineering ?

If you think it's the airbox, then make use of tie wraps or tank tape to secure it in place. If the knock disappears you know you have diagnosed the problem, if not keep looking...  ;)
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Steve McF

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Re: The mysterious knock that got through the MOT last year
« Reply #9 on: 16 August 2019, 10:50:16 AM »
Carrera, you don't work for JLR, do you? :D :D :D ;)

carrera

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Re: The mysterious knock that got through the MOT last year
« Reply #10 on: 16 August 2019, 11:07:04 AM »
No, but are you suggesting I should apply for a job there ?  :)
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Steve McF

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Re: The mysterious knock that got through the MOT last year
« Reply #11 on: 16 August 2019, 03:59:06 PM »
Sounds like you have the right mindset for our workshop :D

aerojon

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Re: The mysterious knock that got through the MOT last year
« Reply #12 on: 16 August 2019, 06:04:53 PM »
difference between the 2 boxes is that the MY03 b207 has an extra pipe which goes onto the front of the top section of the airbox which on the later ones were capped off..

your airbox has been removed at some point,you can clearly see in the plastic where the bottom mount should be..
« Last Edit: 16 August 2019, 06:09:08 PM by aerojon »

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Re: The mysterious knock that got through the MOT last year
« Reply #13 on: 16 August 2019, 08:31:00 PM »
I've found a picture from our old 2003 9-3.  It shows the secondary air injection pipe connection to the air filter.  It should be blanked off on your car and the pipe will be missing.
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Steve McF

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Re: The mysterious knock that got through the MOT last year
« Reply #14 on: 17 August 2019, 12:41:38 PM »
So at a 56 plate, do you think I should have this extra pipe? Where does it go and what was it for?