Did I find the weakest link?

[Brady Moffatt]

Might an ISV be forced to act like a reluctant blow-off valve when the
throttle is closed quickly? Seems to me like there might be a pretty serious
pressure pulse under those conditions, especially if the bypass/blowoff
valve (5ktq have those, right?) is not up to the task.

Jim Green's solution avoids that problem, right?

Cheers,
Brady
Urq, 4kq, Z

-----Original Message-----
From: quattro-bounces at audifans.com [mailto:quattro-bounces at audifans.com]On
Behalf Of JShadzi at aol.com

Cody, over pressurizing an ISV shouldn't really be a problem as they have
more or less equal pressure on both sides of the valve, the pressure
differential across the valve is typically nill.

Now, if you're just venting one side directly to atmosphere, and not back
into your intake system, then it would be understandable why you're having
so many failures, I doubt the valve is designed to hold a 1.5 BAR pressure
differential.

Javad

>I've been waiting on my 5ktq to show me the weak points on these cars for a
while now, and basically I have been just running too much boost. Until this
Saturday I had been on the road for a year between 2 5ktq's (each for
roughly 6 months continuously) running 2.5bar with not even the slightest
sign of anything even dreaming about breaking,except about 2 months ago I
had an ISV get stuck wide open which I though was just a plain failure by
age. Saturday night though after a long 4th and 5th gear boost run I went to
downshift and exit the highway and noticed my engine was idling at 2300rpm.
After checking all of the vacuum lines and finding them to be perfect (was
fairly confused at this point, all hoses ok, throttle fully closed) I
remembered that last time my ISV went bad it did about the same thing. After
squeezing one of the rubber connections with the engine running I found that
the ISV was indeed the issue. For the ride home I plugged up the valve with
a piece of a sho!
>p rag and turned up the idle with the TB screw. I'm going to go ahead and
remove the valve for good now and plug the holes on the manifold.
>
>Anybody else heard of ISVs failing because of being overpressurised? Maybe
I'll see what I can do about repairing it and find out exactly what went bad
inside.
>
>-Cody Forbes
>http://www.500tq.com
>'86 5ktq
>'87 5ktq EFI/K27 and now manual idle adjustment
>'88 80 4cyl
>'88 90 4cyl