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Discussion Starter · #1 · (Edited)
Hi -

I have a '95 900 2.3l that has started to make an odd engine noise that sounds like an air horn. See youtube link below to hear it. The noise is coming somewhere from the rear passenger side of the engine but I can't be more specific.

About 2,000 miles ago I replaced the timing chain using the "pull through" techinque and it's been fine since. Total engine miles are about 125k.

The video is pretty self-explanatory. Anybody got any ideas?

http://www.youtube.com/watch?v=cZ3Z4TVZwdk&feature=youtu.be

UPDATE: I spent some time today trying to narrow down the source of the sound and it appears to be coming from the carburetor! What could cause that?

Details: When I first started it this morning with the engine cold it made no noise at all. Whine started when the engine warmed up. I removed the belt with the engine warm and the noise continued. I removed the big plastic air cover from the carb and it appears to be coming from inside the carb as the sound wavers when I cup my hands over the carb. The sound also goes away when I rev up the engine. The inside of the throat of the carb appears to have some brown stuff in it, and I've noticed that the car has been running a bit rough recently, with the engine idle speed fluctuating sometimes and intermittent low-speed stalling. I'm thinking of blasting some carb cleaner down the throat to see what happens. Any other ideas?

Thanks!
 

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Can you be serious about this "carb" ?
Well, I'd get rid of it and do a restoration, including remounting the inlet manifold..Or, did someone install a base 2.0 liter 4 with a SU unit , from an old '73 Saab 99 ??
Seems impossible.
Seriously,do the engine minor tune up..
 

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Discussion Starter · #4 ·
I guess I should have said "throttle body" rather than carb. Question remains, what could be causing this noise? What is the engine minor tuneup?

Thanks
 

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Could that whine be the starter not disengaging? Look there.
 

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I'd try it again tomorrow when the car is cold, then hot, see if that's a reliable piece of data.

Do you have a mechanic's stethoscope that you could use to try to pin down the location?

Your TB should be clean, but I can't see how a little schmegma would cause a noise like that.
 

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Discussion Starter · #7 ·
Fox - it's not the starter - clearly coming from a different area.

Bob - I'll try that (though it may be a few days!) and also video my diagnosis that it's coming from the throttle body area.

Thanks !
 

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Fox - it's not the starter - clearly coming from a different area.

Bob - I'll try that (though it may be a few days!) and also video my diagnosis that it's coming from the throttle body area.

Thanks !

The starter is in that general location.
 

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Hi -

I have a '95 900 2.3l that has started to make an odd engine noise that sounds like an air horn. See youtube link below to hear it. The noise is coming somewhere from the rear passenger side of the engine but I can't be more specific.

About 2,000 miles ago I replaced the timing chain using the "pull through" techinque and it's been fine since. Total engine miles are about 125k.

The video is pretty self-explanatory. Anybody got any ideas?

http://www.youtube.com/watch?v=cZ3Z4TVZwdk&feature=youtu.be

UPDATE: I spent some time today trying to narrow down the source of the sound and it appears to be coming from the carburetor! What could cause that?

Details: When I first started it this morning with the engine cold it made no noise at all. Whine started when the engine warmed up. I removed the belt with the engine warm and the noise continued. I removed the big plastic air cover from the carb and it appears to be coming from inside the carb as the sound wavers when I cup my hands over the carb. The sound also goes away when I rev up the engine. The inside of the throat of the carb appears to have some brown stuff in it, and I've noticed that the car has been running a bit rough recently, with the engine idle speed fluctuating sometimes and intermittent low-speed stalling. I'm thinking of blasting some carb cleaner down the throat to see what happens. Any other ideas?

Thanks!

How about your alternator. It's right in that area. maybe bushings or bearings are making that noise or your belt?
 

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I would tend to agree with an alternator or maybe another accessory like the A/C compressor or power steering pump. You removed the accessory belt and ran it though? Noise continued? Could also be something inside the timing cover. Doesn't sound like an air leak to me though. Most likely a bearing or bushing of some sort. Could it be a camshaft sound?
 

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Discussion Starter · #12 ·
Thanks for the input. I did remove the belt and the noise continued, so it can't be alternator/pulley. I recently replaced the timing chain so doubt/hope that's the problem. The sound it made before doing that was more of a rattling noise rather than this high pitched sound.

I will make a new video in the next few days to illustrate, but here's the symptoms thus far:

- Didn't make the sound on cold start
- Seems to be most apparent at idle and disappear under load/higher RPM's
- Not related to belt
- Sound seems to be coming from throttle body. With air intake removed, if I put my hand over the TB the sound decreases.
- Really sounds like an air horn. When the engine is shut off, it kind of trails off briefly rather than stopping abruptly.

Thanks!
 

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Do you have the ability to do a "boost leak test"? It will help you figure out if there is a leak in the intake system.

I removed the rubber coupler between the air filter box and the hard turbo inlet pipe, attached an air compressor in its place (with an adapter to fit onto the turbo pipe), and the used the air compressor to pressurize the intake system. This way the engine isn't running, and you can listen for air leaks.
 

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Discussion Starter · #14 ·
Good idea, I can give that a try. It's not a turbo though, so I wonder if I should be pressurizing the intake manifold?
 

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Could it be a serious vacuum leak where the throttle body joins the intake? As you accelerate manifold vacuum tends to decrease and that would explain why it is louder under idle????

I have heard bad carb to manifold seals in carbed cars make a similar sound at idle.
 

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Discussion Starter · #16 ·
Did some more investigating and took a new video (link below). Here's what I found:

- The sound appears to be coming directly from the mouth of the throttle body. I say this both as that's how it sounds to my ear and as in the video when I wave my hand over the mouth of the TB the sound is noticeably muffled.

- It does not sound like it's coming from the area of the timing chain, nor does it have a rattling tone. Sounds just like an air horn.

- When the engine is turned off, it briefly fades away. Again, like escaping air.

- I checked the four bolts that hold the TB to the manifold and all are tight. No obvious leaks, broken hoses, etc.

- There is some brownish gunk in the TB (visible in the video). Is this excessive?

- As the video shows, when the throttle is opened the sound decreases.

Nosajwols - a vacuum leak would indeed seem to be a likely candidate. I seem to recall from high school auto shop that you could spray some fluid around a carb to check for vacuum leaks, if there were any the engine would suck it up and run rough. Does anyone remember this trick?

http://youtu.be/J-2ZXv2Cz5I
 

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It works

I've done that many times in the past. Use brake or carb cleaner, not wd40. This method works well.
 

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Have you checked your vacuum hoses? Maybe the connections are loose. Do any of the hoses pull off easy. I would think it would be a large vacuum hose or a hose around the IAC valve. It could be under pressure that your vacuum hose is singing at a connection because the hose is loose. Also check the hose and the connector at the Valve cover. If that grommet is old it could be very loose.

Now, here is the other idea. Have you checked your intake manifold to throttle body. I"m not sure but if there is a gasket between the throttle body and the intake manifold, could it be loose or broken. It sounds like your playing a kazoo. Also, you did check that your bolts to the intake manifold and throttle body are tight. If there is a gasket between them and it was damaged or broken, I could see it sucking air through a small crack and maybe cause that noise. Not only that but also check your intake manifold to the engine. Make sure those bolts look tight and see if there could be any leaks.

It can be dangerous but you use starter fluid to check for leaks. You want to make sure you engine is cold when checking. It's possible a hot engine could ignite the fluid. But when you spray it, your engine responds when the gas enters the engine through a vacuum leak. You only spray it around areas you think are sealed. If your cover is off, then the fluid will just get sucked in the throttle body.
 

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Re

It might be the boost recirculating valve or on my car the BOV I think its the bosch unit on yours and they do fail and make a honking noise.Good time to install a BOV. Disregard I thought it was a turbo.
 

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You would still be fine pressurizing the intake system on a non-turbo car. You would only need to go to ~5 or 10 PSI to hear your leak.

Spraying the area with carb cleaner/starting fluid is probably an easier method though considering it does not have a turbo.
 
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