Rev Limiters (was RE: Knock Sensor Q)

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

Thank you Jonas. Now we definitely know the knock box has a rev limiter
roll.
But, the strange thing is, awhile back my fuel pump relay died. (the car had
no rev limiter I was aware of, at least 7200) I swapped in a FPR out of an
86 8V Scirocco (ie. non-knock box) and acquired a 6200 RPM rev limit.
Subsequently, replacing the relay with a new one restored the lack of a rev
limiter.
So, the bottom line is the knock box definitely has a rev limiter if the car
is wired to use it.
But, some FPR's also have a rev limiter that will function no matter what
ignition system you have.
just my .02$

----- Original Message -----
From: Jonas K. <jkarlsso@metabolex.com>
To: scirocco list <scirocco-l@scirocco.org>
Sent: Friday, May 24, 2002 1:40 PM
Subject: Re: Rev Limiters (was RE: Knock Sensor Q)


> Hi all,
>
> I perused the wiring diagrams in the A2 bentley last night, in search of
an
> answer to this question.
>
> Here's what I found:
>
> All the A2 cars have the following pin designation on their FPR's:
>
> 30: Always 12v
> 15: switched 12v
> 87: output to power fuel pump
> 1: goes to coil/ignition control unit
> 31: either ground or to knock box.
>
> On the low compression cars, terminal 31 goes directly to ground, and in
the
> High compression cars, terminal 31 goes to terminal 10 on the knock box.
>
> So the knock box does _not_ trigger the FPR's activation, that's still
done
> by the coil, the box merely provides the ground, which it can interrupt
"at
> will".
>
> I forget who said the knock box gave a pulsed ground, but from these
> diagrams it seems that the knock box provides a full-time ground until the
> rev limit is reached.
>
> This is why Honnold's solution worked. He tee-ed the wire from terminal 10
> on the knock box into the ground wire for the FPR. Thus, even when the rev
> limit was reached, the FPR is grounded. Elegant.
>
> When I installed the knock box for my 2.0 (aba/JH) install, I left the
wire
> from terminal 10 unconnected. It'll work fine.
>
> A neat experiment in the real world would be for someone with a 16v
(keeping
> it scirocco specific), who knows what it's like to bounce off the rev
> limiter, to tap in a ground for the wire from pin 10 on the knock box.
>
> Then do back to back test with this tap _not_ connected to ground (rev
> limiter enabled) vs. with the tap grounded (rev limiter disabled).
>
> Let us know what happens when the knock box is pushed beyond the preset
rev
> limit, and how high it will rev. Also let us know at what point the motor
> blows up. :-)
>
> If no-one steps up to the plate, I'll just have to wait a couple of weeks,
> then try it on my brother's POS discarded beater 86 GTI.
>
> Jonas
>
>
>
>
>
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