Re: 5KCSTQ: fuel enrichment

[Nick Craft <ncc@scr.siemens.com>]

<O>On Mon, 8 May 1995 PDQSHIP@aol.com wrote:
<O>
<O>> I'm not referring to O2 directly, I'm referring to the freq valve in the fuel
<O>> dist.....  the turbo motors should read 50% dwell +/- 8%....  A freq valve is
<O>> operates on the same theory as a set of points, you have a open and a closed
<O>> cycle....  The Audi techs don't use any special tool for this setting (at
<O>> least they don't need to), don't make this procedure too complicated, it's
<O>> dwell and the spec in the manual IS a dwell reading, to check full throttle
<O>> you should see about 70-80% dwell.....
<O>
<O>I'm not making it complicated! Your method of testing through the frequency 
<O>valve is valid. BUT, understand that the frequency valve is regulated by 
<O>many other factors, sensors included. Therefore, would it not be wiser to 
<O>test by the O2 sensor, which is the final 'word' of how well the engine 
<O>is burning? What if the coolant sensor is faulty? it affects the 
<O>frequency valves performance, as does the O2 sensor. Of course one may 
<O>have a faulty O2 sensor as well, but it is only one variable, not many. I 
<O>still preffer to test via mili-volts thru the O2 sensor, although 
<O>ideally, the picky enthusiast would try both ways, or even use a 5 gas 
<O>analyzer!
<O>r.mair

I've used both these techniques on my car and they're both useful. I'd point
out one thing - old Oxygen sensors can fail by getting "slow", so even though
you see them going up to ~ 0.8 V as you tweak the mixture screw, their transient 
response is such that they're unable to keep the mixture correct under varying 
load/throttle conditions. Also the duty cycle of the freq valve can be misleading
under the same circumstances for the same reason - it looks like it's doing what 
it's supposed to, but you still get transient mixture problems.

Nick Craft