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

[Cody Forbes]

Well to start with the fuel lines will pulse to match the injector firing,
which is once for every cylinder firing. I can't say that I've heard
anything fuel related that knocks and changes sound based on engine temp, so
I honestly wouldn't start there. I have MS'ed 2 5ktq's and, yes, you're
correct they shouldn't make any noises that they didn't with CIS other then
injectors firing (my more recent one has 43lb/hr injectors, bigger = louder)
which sounds alot like lifter tap. Does this noise sound anything like a rod
knock (would get quieter as oil pressure builds)? How loud of a knock are we
talking about here (clearly audible inside the car, windows up, sunroof
closed, or is it an under the hood type of thing)?

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.

This also works well on exaust leaks, use some rubber hose to 'sniff
arround' where you think you have an exaust leak and with your ear held to
the other end you will pinpoint the leak quickly.

-Cody Forbes
Black Forest Racing
http://www.500tq.com
'86 5ktq
'87 5ktq EFI k26/k27
'88 80 4cyl
'88 90 4cyl


----- Original Message ----- 
From: "Jeff Redig" <birdmanmt at juno.com>
To: <quattro at audifans.com>
Sent: Tuesday, January 13, 2004 11:51 PM
Subject: EFI and a fuel knock.........


> Hi all,
>
> the car discussed here is an 87 5k tq.
> This fall i converted the car to EFI with the megasquirt DIY efi system.
> It runs quite well now, better than i ever did on CIS!
>
> I've got an issue with the car, or at least i think i do, concerning the
> efi system and someone recommend i post here and see if anyone has any
> ideas.  So here we go....
>
> As i said above it runs really well with the EFI, however i'm getting a
> knock in the fuel system.  I don't really know how else to explain it.
> At first i thought the accumulator might be going bad.  Is there a way to
> test it?  I now think it's just because the accumulator makes contact
> with the undercarriage making the knock/pulse the most audible there.
>
> So when the car is cold it knocks loudly....but as it warms up it gets
> quieter.  It's still there but not as audible.  If i put my hand on one
> of the fuel lines under the hood there is a definite pulse i  can feel.
> It matches the injectors firing exactly.  As far as i
> know the other people running MS on these cars don't do this though, and
> haven't had this knock/pulse problem which leads me to believe it's a
> unique problem on my vehicle.  Meaning something's broken!
>
> My other thoughts lead towards my fuel pump and a fuel dampner.  I've
> replaced my fuel pump with a pierburg which doesn't have a dampner on it.
> So there isn't a dampner in the fuel system anywhere.  I'm wondering if
> this would take care of the knock?  I don't know exactly how a dampner
> works....some sort of a diaphragm.
>
> Any thoughts or considerations would be much appreciated!
> happy quattroing
> Jeff Redig
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