Author Topic: Wobbly turbo gauge - ng900, 140k  (Read 141 times)

jimmym105

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Wobbly turbo gauge - ng900, 140k
« on: 11 July 2019, 03:37:20 PM »
Chaps - any pointers of where this probloem might lie gratefully received. The turbo gauge wobbles when idling. Rev counter static, but can hear the tiniest change in revs. Any thought? Thanks in advance

carrera

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Re: Wobbly turbo gauge - ng900, 140k
« Reply #1 on: 11 July 2019, 03:43:01 PM »
I'm going to guess that the turbo gauge is old school pressure tube operated and it has a small hole in it which can open / close allowing the fluttering and also a small variiation of airflow into the engine.

I know virtually nothing about NG900, but just an idea until someone who knows more comes along
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sgould

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Re: Wobbly turbo gauge - ng900, 140k
« Reply #2 on: 11 July 2019, 05:18:26 PM »
Yes, the early cars have a direct tube from the gauge to the engine.  There should be a plug in the tube with a small hole to stop it all fluttering too much. A cheap damper.  Has anyone replaced the tubing and just left it full bore all the way?  At the age of your car, it's likely that quite a bit of the rubber tubing has been changed, or is in need of changing.
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jimmym105

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Re: Wobbly turbo gauge - ng900, 140k
« Reply #3 on: 11 July 2019, 05:36:56 PM »
You guys are brilliant, thanks for quick responses. I'll see what I can find

carrera

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Re: Wobbly turbo gauge - ng900, 140k
« Reply #4 on: 11 July 2019, 06:07:24 PM »
You could also nip off the pipe near the offtake point as a test. If the tickover becomes smooth then it's definitely a hole in the tube that is causing the idle variation
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jimmym105

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Re: Wobbly turbo gauge - ng900, 140k
« Reply #5 on: 20 July 2019, 05:43:21 PM »
Chaps, by way of an update, and again, thanks. Have done 400 successful miles in the old beast since I last posted and although I cannot spend too much time looking at the wobble for obvious reasons (!), it seems to dissapear when car is hot, and has been for a while. I've now taken a look at all the hoses.

The one I assume goes directly to the gauge - as it dissapears into the bulkhead on the drivers side - is original, judging by the amount of grime on its small white sticker and the zip tie looks ancient. It's in good condition. What I did find was that the clear hose that comes off the breather nipple is not attached to anything. So it looks like it should go between the two large pipes beneath the turbo (attachment) so I have attached it and fired it up and after some initial wobble when idling it calmed down and was still (or almost still, the kind of wobble one would never spot unless looking).

I am a true novice on cars, does this sound right?!

Just spotted Carrera's post - will give that a go ASAP.

carrera

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Re: Wobbly turbo gauge - ng900, 140k
« Reply #6 on: 20 July 2019, 06:06:19 PM »
Did I mention I don't know much about ng900's

Well anyway, that clear pipe is connected to the crankcase breather, and the other end of that pipe should I believe be connected onto the throttle body, so that excess crank pressure gets fed back into the engine. Look for a metal spigot with nothing connected

........... or is that someone's bodge with a screw and piece of rubber on the left hand side of the inlet pipe, blocking off the air leak because the pipe was not connected at some time ??
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jimmym105

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Re: Wobbly turbo gauge - ng900, 140k
« Reply #7 on: 20 July 2019, 06:34:10 PM »
You'll know more than me! Thanks, we might be alright then. That screw with rubber, well, it's got a round head and looks like you couldn't turn it...

carrera

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Re: Wobbly turbo gauge - ng900, 140k
« Reply #8 on: 20 July 2019, 08:22:22 PM »
I have been reading around. That rubber bush / metal bit is standard.

This page should be useful for you

http://www.saabwiki.info/index.php?title=NG_900/9-3_Throttle_Body

I suspect that the clear pipe should go to 5 in diagram 7.

Note particularly figure 3. There is an idle control circuit, so you need to make sure that those hoses are in good condition with no leaks.
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jimmym105

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Re: Wobbly turbo gauge - ng900, 140k
« Reply #9 on: 21 July 2019, 08:53:28 PM »
Many thanks for this, will take a good look around asap