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I have a '91 BMW 325ic convertible. 6 cyl. Two days ago, the car started "trembling" while in idle. First I thought it was a failing engine mount, but you can distincly hear a "hiss" on the firewall side of the engine. The hiss continues for half a second after turning off the engine. I suspect a vacuum leak. Had a vacuum leak repaired over 18 months ago. Records currently not handy so I can't indicate what was repaired. I believe it was a hose however. Is there a basic technique mechanics use to determine the location of a leak either from a hose or a gasket similar, for example, to determining an air leak from a tire (like spraying the area with water)?

Submitted: 342 days and 8 hours ago.
Category: BMW
Value: $20
Status: AWAITING CUSTOMER ACTION
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Optional Information

1991 BMW 325ic conv. 6 cyl

Already Tried:
Just cursory inspection. I have not attempted to fix repair.

Posted by jeffrey590 342 days and 2 hours ago.

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jeffrey590 : Greetings XXXXXXXXXX,
jeffrey590 : try spraying carburator cleaner in the area you hear the hissing from while the engine is running...When you hear a change in idle quality and/or speed , you've located the leak...also try area by brake booster and related hoses...jeffrey590
jeffrey590 : NO ...I have used this method many times in the past and have had no problems...These days we use what is called a "smoke machine"...it is used to find small leaks in the evap system...but obviously the do it yourselfer doesnt have access to this tool; so the previously mentioned method is the next best thing...jeffrey590

Posted by Anthony 341 days and 14 hours ago.

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IGUANALUVU :

:)

Anthony :

Is there anything else you would like to know?

Anthony :

The simplest technique is what is called "smoke testing". Have a mechanic with this tool pump smoke into the intake manifold and within 10 seconds the leak will be obvious. This is the safest and most accurate way to find a leak without spraying flamable liquids at a hot engine. Most shops have this tool and will be able to locate the leak without any guessing.

IGUANALUVU :

Thanks Anthony. Probably something I can't do myself, but I'm just curious, where on the intake manifold do they attach this device? Is there an access port or do they detached the manifold from the engine or attach the device via the tailpipe?

Anthony :

They attach a lid that look like a coffee can lid to your throttle. Then through any vacuum hose inject the smoke. It works every time. Also the labor charge is less than an hour, so its definately worth it.

IGUANALUVU :

Wow. Terrific! I've learned something new. So I figure if I keep asking you guys enough questions over let's say four or five years (my Beemer will certainly provide the opportunity), I can apply for my mechanic's license!

Anthony :

Glad to hear it and thank you for asking.

Anthony :

Hi!

IGUANALUVU :

Thanks Jeffrey. Appreciate the follow up.

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Expert: jeffrey590
Pos. Feedback: 95.2 %
Accepts: 52
Answered: 4/11/2009

ASE Master Technician

ASE Master Technician , Master Technician w/ 35 years Dealer Experience in Advanced Level Diag.

Posted by Anthony 341 days and 4 hours ago.

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