Rev Limiters (was RE: Knock Sensor Q)

[marc_scirocco@yahoo.ca (Marc scirocco Québec)]

The fuel pump relay is more than just a relay. There
is a circuit in there that picks up a pulse from the
coil, blends it with a 555 timer (IC), and that gives
it a solid signal to drive a transistor, and then to
drive the actual relay (more or less that way).

This is done for safety reason: as soon as the motor
stops physically turning (like in an accident), the
fuel pump stops working, after a second or two.

Of course, since it picks up a signal from the coil,
it can shut the pump at a desired preset.

Simple, yet brilliant!

Cheers.

Marc
'83 Scirocco
'88 Scirocco Slegato

 --- Cory Langford <cory.langford@icbc.com> a écrit :
> 
>  Just a wild thought here. 
> 
> If the Knock Box tells the Relay when to shut down
> the fuel pump, I
> would suspect that would be done via a voltage/no
> voltage situation to a
> specific pin from the box to the relay.
> 
> So if that wire was cut (the connection between the
> relay and the knock
> box) would not the rev. limiter be removed?  If
> there was a need for
> voltage, I am sure you could connect the correct
> voltage from another
> source to keep the fuel pump working.
> 
> I do realize this brings up other issues, like
> safety if the engine cuts
> out and the fuel pump keeps on going, but who needs
> safety for a engine
> that can rev till it fly's apart :)
> 
> 
> 
> 
> -----Original Message-----
> From: Jonas K. [mailto:jkarlsso@metabolex.com]
> Sent: Thursday, May 23, 2002 9:57 AM
> To: ATS - Patrick Bureau; scirocco list; Chris
> DeLong
> Subject: Re: Knock Sensor Q
> 
> 
> On 5/23/02 6:43 AM, "ATS - Patrick Bureau"
> <pbureau@attbi.com> wrote:
> 
> > you know I read your replies 3 times... and you
> make no sense what so ever.
> 
> Aagh, sorry, guess that's what I get for trying to
> be thorough. :-)
> 
> > 1. you are saying that the 8v and 16v knock box
> are the same (or you don't
> > know)
> 
> Yes. :-) Don't know for _sure_, but they should have
> the same wiring.
> Best
> bet would be to use a harness and box from the same
> (8v or 16v) that way
> you're safe.
> 
> > 2. then you say the relay has nothing to do with
> it, but the cut off is
> > controlled by the knock box
> 
> What I meant is that the relays between the RD 8v's
> and the PL 16v's are
> the
> same. The knock box controls at what RPM the relay
> shuts off the fuel
> pump.
> 
> > now if the knock boxes are the same and the relays
> are not the controlling
> > device, how does the
> > knock box know its controlling an 8v (6800Rpm) or
> 16v engine (7200 rpm) and
> > adjust itself to the proper engine?
> 
> Aha, I see the confusion. The 8v and 16v knock boxes
> have entirely
> different
> part numbers, and somewhat different interals. They
> are clearly not the
> same. The main diffenerce AFAIK is that the rev
> limits are set
> differently
> between the two. I thought this was understood, and
> that the question
> was if
> a 16v knock box would connect up to an 8v harness
> and be a plug-n-play
> bump
> up in the rev limit.
> 
> > what I want to know is
> > what controls the rev limitation (knock box?
> relay?) if knock box, then
> > logic dictates that an 8v and 16v knock box would
> be different JUST because
> > they rev limitator are set different  (no matter
> if they are wired the same)
> 
> The rev limit is strictly set by the knock box. The
> 8v is different in
> this
> respect from the 16v.
> 
> > and btw.. I am talking about SCIROCCO here not A2.
> 
> Right, I got that. What I was telling you is that
> when you put the
> knocksensing system into your scirocco, you will
> retain your stock fuel
> pump
> relay. This one does not take an input from the
> knock box, so regardless
> of
> which box you use, you will not encounter a rev
> limiter.
> 
> I've got the 8v system in my 85 and in my 78, no rev
> limit other than my
> right foot, and frailed nerves.
> 
> Hope that cleared things up, sorry for the
> confusion.
> 
> Jonas
> 
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