Adam, I'm not sure we're on the same page here about vacuum leaks. Yes, there's vacuum that's used to assist the brakes (assuming that the 90 had the old/new vac. assist brake system), adjust the climate control, etc. That vacuum may be generated by an electric pump (like the power lock system) or a cam driven pump (like on the old 4k's) or syphoned off the engine intake using a check valve. When the (non-turbo) engine is running, the engine produces a vacuum - that is why air flows into it. There's a measuring device (in my 5k's, it's the CIS airflow meter) that figures out how much fuel to put in based on the amount of air flowing in. Between the meter and the engine, there's a vacuum. If there are any leaks in the plumbing between meter and engine, then unmeasured air will enter the engine and the mixture will get screwed up. From what I understand, the Smoke Test pressurizes the intake and leaks will let the smoke out. Most leaks will be found with this test, although I've heard that some leaks let air in, but tend to seal under pressure. The Bentley test is a good indicator of leaks in vacuum lines - which may be connected to things like emission controls, timing advance, etc. in which case the test is good. A Mity Vac is good for these tests, too, and gives you a gauge to read the leakdown. The test will not uncover leaks in any of the intake hoses, though. The propane gas test will suck in propane into the system, causing an increase in rpms - when the engine is at operating temperature and idle is stable, you'll have a fairly high intake vacuum to test with. Obviously, this is not a test to be done in a closed space....but you wouldn't be idling a car in there anyway, right? Cheers! Steve Sears
1987 Audi 5kTQ
1980 Audi 5k
1962 and '64 Auto Union DKW Junior deLuxes (SPAM Blocker NOTE: Remove SHOES to reply)
"Adam" wrote in message news: snipped-for-privacy@4ax.com...
looking through my new 1,800 pg Bentley factory guide, they provide a
> different way of testing the vacuum system, I don't have it in front
> of me at the moment but this is how it goes:
> take the hose off the vaccuum motor(pump)
> put your finger over the end of the hose
> pull the linkage from the vacuum servo until it's fully extended
> if the linkage returns there's a problem w/ the servo
> if it doesn't there's a problem with one of the hoses or clamps
> or there's a problem with the vacuum vents by the pedals
>
> I haven't attempted this method yet, I just got my manual yesterday.
> Any chance of visually inspecting the hoses?
>
> Talking to an import garage, the smoke test is an actual smoke machine
> that they connect to the system and just look to see where the smoke > is coming out..??
>
> I'll be attemping this inspection in a couple days....keep you posted > Adam
>
>
> On Mon, 29 Mar 2004 10:12:35 -0500, "Dave Smith"
> wrote:
>
> > steve's right adam, the best all be it rather unorthodox way to find a vac
> >leak is with the propane torch or any other flammable gas. dont be afraid to
> >do this, just be careful and follow obvious saftey issues.
> >
>