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And if it leaks, you'll also get idle problems
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Posted by BillJ (more from BillJ) on Sat, 3 Aug 2002 17:02:13 Share Post by Email
In Reply to: Re: Function of ECO tube?, Jim kane, Sat, 3 Aug 2002 14:05:26
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This hose communicates manifold pressure to the bypass valve which keeps the valve closed when the manifold pressure is hig (under boost) and opens it, as Jim Kane says, to dump boost out of the inlet when you lift off the throttle (making the "hiss" that some people think is so "cool").

So if it leaks, this function won't work. What will happen is that the hose will be supplying atmospheric pressure to the bypass valve. When the boost pressure rises a bit above atmospheric pressure, the valve will open and boost will leak away.

Also, a broken hose will let air into the inlet manifold that shouldn't be there. At idle (when there isn't much air going into the manifold), this is enough to make a big difference. On cars with an air-mass meter, this makes the mixture weak, as the leaking air has not been measured and no fuel provided for it. The engine will idle roughly, if at all. On Trionic engines, the air mass is calculated at the inlet manifold, so the extra air will be accounted for and fuel will be provided for it. Therefore, this will tend to make the idle speed rise. The idle speed control valve may be able to compensate, and may not.

Anyway, replace the hose. It took me 10 minutes the other day and cost around £10 (US$15) at a local parts shop for 3m (10ft) - over twice as much as I needed for that (I bought some extra for one of the other cars). I wouldn't consider not replacing something broken on the engine.

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