knock system questions...

[jdbubb@ix.netcom.com (Dan Bubb)]

The knock box is a map based system. In other words it uses two basic inputs
to determine ignition advance. On top of the two basic inputs are 3
additional inputs that are used to modify the amount of igniton advance.
The two basic inputs are RPM, to determine the, uh...RPM! and intake
manifold vacuum to determine engine load. The vacuum port musted be
connected to manifold vacuum, not ported vacuum. Don't connect it to the
vacuum port on the TB. Connect it to a port on the big assed vacuum hose
that goes to the brake booster.
Typically, as RPM increases the ignition advance increases until you get to
a certain RPM (~3500-4000) after which it will stay constant.
Easy to test. Just disconnect the vacuum line from the unit and watch for
igniton advance as the engine is revved.
Also, as vacuum increases the ignition will advance. This is more difficult
to test because the amount of vacuum/load based advance depends on RPM. I'd
test it by holding the engine at 3000 RPM with the vacuum hose disconnected
then check advance while sucking/pulling a vacuum on the hose.
The 3 additional inputs are; idle switch, full throttle switch, and knock
sensor.
The idle switch tells the knock box to not to adjust advance due to engine
vacuum while idling. This gives a nice stable idle and allows consistent
timing to set the advance. If this switch isn't working the advance will be
more than it should at idle and the total advance under load will be less
(way less) than is optimum for power. (provided your vacuum hose is hooked
up to manifold vacuum)
The knock sensor, of course, alerts the knock box of knock. The box will
retard timing until knock goes away, then try to readvance timing to the
base number unless knock reappears. The knock box does not try to keep
advancing from the base map value until it senses knock. The base map value
is, presumeably, optimum for power and the until only retards from that
value if knock is sensed.
I'm not sure what the full throttle switch does, but I suspect it again
tells the knock box not to look at manifold vacuum and just use the base WOT
settings.
I'd check that the unit is advancing based on the RPM test and vacuum test
above, and check for correct operation of the full throttle and idle
switches.
Hope all that was clear.
Dan


----- Original Message -----
From: Michael Abatzis <abatzis2@hotmail.com>
To: <scirocco-l@scirocco.org>
Sent: Monday, April 28, 2003 6:27 PM
Subject: knock system questions...


> still can't figure out why the car is slow.  went to the yard, pulled the
> knock/fuel boxes from an audi 4k. it ran a little strange, so i checked
> timing and for some reason it was way advanced. i thought i found my
> problem, retimed, but still slow. questions:
>
> 1. is the knock box and fuel ecu the same on the 4k? look the same, have
> different part #'s. i was wondering if the ignition map might be a bit
> different (hence the screwed up timing).
> 2. a basic knock sensor question: how the hell does it work? does it
advance
> it a certain amount (the 13' that bentley says?) and retard based on knock
> sensor input, or does it keep advancing till it senses knock, then retard
a
> certain amount? some combo of the 2?
> 3.  what is the vacuum hose input for?
>
> still pretty ticked at this car...
>
> -Michael Abatzis
> Hotlanta! GA-->Soon to be New Orleans!
> 1988 Scirocco 2L 16v RIP-->parting, finally taking orders:
> www.learnlink.emory.edu/~mabatzi/mikes_page1.html
> 1987 Scirocco 2L 16v...
>
>
>
>
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