Re: TECH: Quantum Syncro/Audi 4000CSQ Engine questions

[steveb@falcon.kla.com (Steven Buchholz)]

> I hear that this clicking is common in 10v 5cylinder engines.  I have heard
> it could be a vacuum leak, cracked or loose exhaust manifold, or 'tappet noise'.
> The clicking goes up and down with RPM...and does not seem to affect power.
> The car was pretty peppy.
> 
... can come from one of several sources ...

1) There is an auxiliary vacuum pump driven from the cam to ensure sufficient 
   vacuum for brake boost.  The pump can make a knocking noise as thedrive 
   rod knocks on the cam.  For this model it seems that this may be the most 
   likely cause.

2) These cars have hydraulic lifters.  For some reason the Audi lifters tend 
   to be noisy.  I'd rate this #2 in likelihood.  This noise should be more 
   noticeable when the car is started after sitting for a long time ... but 
   may come and go randomly based on engine RPM and who knows what else ...

3) broken exhaust studs and a warped manifold.  This would be least likely 
   IMHO, but you may notice that the noise is much louder when the engine is 
   cold, and is louder when the engine is accelerating (even when sitting still).

The fix for #1 for some people is simply to remove the rod and count on mani-
fold vacuum for brake boost.  I find that an oil change tends to fix #2; and 
that the lifters get noisier when the engine oil is approaching a quart low.  
I fixed the problem temporarily by using some cleaner that I put in the oil a 
few hundred miles before changing it.  Number 3 you might simply want to live 
with.  This sort of problem usually goes away when the engine warms up.  Other-
wise you're talking about pulling the manifold to get it resurfaced and pos-
sibly the head to get out any broken studs ...

HTH!
Steve Buchholz
s_buchho@kla.com
San Jose, CA (USA)