EFI and a fuel knock.........

[Dan Cordon]

> Heres a trick. Get yourself the longest screwdriver you can find, and start
> the motor. Pick out a noisy area (if unsure, start with the head/intake
> manifold) and firmly touch the screwdriver to it (anywhere on the actual
> head in this example, not the valve cover or distributor). Hold your ear to
> the end of the handle of the screwdriver, and viola you have a stethoscope
> (sp?) like your doctor. Touch it to various things that you think may be
> causing the noise and the loudest should be your culprit. Remember though
> that noises will transfer through metal (thats how our little tool works!),
> so if you hear a knock in the head, make sure you check the block too and
> see if it gets louder/quiter. Disclaimer: In no way am I saying this trick
> should be your end-all solution, what it will do is give you a better
> standpoint for further diagnotics and a more defined place to start looking.
>

Jeff, I'm just down in Moscow, ID. Nice to see another quattro owner
from the region :o) I agree with Cody on this....fuel pulsing could be
audible since you're running no accumulator at all. Especially if you're
doing batch fire instead of sequential. But that aside, it shouldn't
change as much with temperature as it would be with engine load or
speed.

On another note....while the screwdriver stethoscope is useful, and
cheap, I've found the real ones to be much better.
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=41966

At $5, I've found these so useful that I've been known to give them as
gifts to car friends. You really don't know what a grand symphony your
car makes until you get one of these!

Are you sure it's the fuel system that's making the noise? That's what
I'd check first. If you're sure, then there's a number of tests that can
be done to diagnose it. Let us know more on the situation.

--
Dan Cordon
Mechanical Engineer - Engine Research Facility
University of Idaho