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Rev Limiters (was RE: Knock Sensor Q)
Patrick, I'm running a similar setup in my 87 Jetta winter beater. I
slapped some RD pistons in a JH block, threw on the JH head with a G
grind, and grafted a knock sensor ignition in from an A2 GLI. I kept the
stock CIS, and the cat-free from factory 87 makes for some fun exhaust
options without having to worry about emissions woes (not that I do
anyways.)
The kock box I used came from an 86 8V GLI, and the fuel pump relay was
the stock 87 Jetta CIS relay.
I didn't think about rev limiters too much when assembling the system.
As a matter of fact, I didn't think about it too much when I installed the
16V instrument cluster with its 8K tach and 260km/h speedo, either. For
some reason I developped a tendency to bounce of the 8V's top end when the
tach needle told me I had another 1000rpm to go before hitting the red...
:)
I generally shift when the power starts to drop off, which is just about
6K anyways (limitation of the G grind?) however one morning I was in a
tight spot and kept into 3rd gear at WOT, and it kept pulling hard until
about 6200, when the engine started to buck like mad. I dropped into 4th
and it started pulling again - my guess is I hit a rev limiter function
that was cutting fuel to the motor.
My fuel pump relay is straight CIS (GX/MZ engines: 321 906 059H - compare
with CIS-E relays for RD/PL: 191 906 383 C) Your 85 Scirocco should have
come with the "059 F" part - heaven knows what subtle engineering change
prompted the shift from F to H.
My expectation, as I believe others have confirmed, is that the knock box
cuts the coil pulse to the relay, which then in turn cuts power to the
pump. This "protection" mechanism, which keeps the pump from pumping an
accident scene full of fuel, has been present in CIS fuel systems for a
long time - I'd have to go back to the wiring diagrams to check, but I'm
pretty sure it was there in 81+ german-built cars. Definitely there in
84+ cars. Running either a 16V or 8V knock box (I'd go with the 8V box if
you're running an 8V engine, personally) with your stock fuel pump relay
should result in a rev limiter - it's just where it is that's the
question.
HTH,
Drew
On Thu, 23 May 2002, ATS - Patrick Bureau wrote:
> but I have a MKII 85, running cis, not converting, just hybrid 3a/jg engine,
> I need a knock box because of 10.5:1 compression.
> does what you just stated (keep my current relay) simply install a knock box
> (which ever no matter 8v or 16v) and it will never have a rev limitator?
>
> ==========================================
> ATS - Patrick Bureau
> 1985 8v **Planning 3A/JH Upgrade**
> 1988 16v ** FOR SALE : 1500.00$ **
> Web Site : http://longcoeur.com/scirocco
>
>
> =>-----Original Message-----
> =>From: scirocco-l-admin@scirocco.org
> =>[mailto:scirocco-l-admin@scirocco.org]On Behalf Of Brian Honnold
> =>Sent: Thursday, May 23, 2002 2:18 PM
> =>To: scirocco list
> =>Subject: RE: Rev Limiters (was RE: Knock Sensor Q)
> =>
> =>
> =>Here's what I did when swapping cis-e into my MkI.
> =>
> =>Keep the stock fuel pump relay and wiretap the ground wire from
> =>the cis-e brain to the correct wire on the fuel pump relay.
> =>
> =>This give you a complete circuit with no rev limiter.
> =>
> =>Brian H
> =>
> =>-----Original Message-----
> =>From: scirocco-l-admin@scirocco.org
> =>[mailto:scirocco-l-admin@scirocco.org]On Behalf Of Ken Bates
> =>Sent: Thursday, May 23, 2002 10:25 AM
> =>To: Jonas K.; Cory Langford; scirocco list
> =>Subject: Re: Rev Limiters (was RE: Knock Sensor Q)
> =>
> =>
> =>This is exactly MY problem and why I started this thread the other day. I
> =>am not getting a ground on the switching side of my fuel pump realy and
> =>suspect my Knock Box is not "completing" this circuit.
> =>I am about to do just exactly what Jonas is saying and jumpering
> =>a seperate
> =>ground to the FPR.
> =>I ma followingthis closely. I appreciate all the input.
> =>Ken
> =>'79 Scirocco 16v project "McFly"
> =>'86 16v (parts car)
> =>VORTEX: "Indiana Red"
> =>
> =>----- Original Message -----
> =>From: "Jonas K." <jkarlsso@metabolex.com>
> =>To: "Cory Langford" <cory.langford@icbc.com>; "scirocco list"
> =><scirocco-l@scirocco.org>
> =>Sent: Thursday, May 23, 2002 11:59 AM
> =>Subject: Re: Rev Limiters (was RE: Knock Sensor Q)
> =>
> =>
> =>> On 5/23/02 10:36 AM, "Cory Langford" <cory.langford@icbc.com> wrote:
> =>>
> =>> > 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?
> =>>
> =>> From my stydy of the system a couple of years back, (i.e. hazy
> =>memory) the
> =>> Knock box actually provides the ground that keeps the relay going. When
> =>the
> =>> rev limit is exceeded the ground is removed and fuel pump shuts off.
> =>>
> =>> Cutting the wire would render the FPR permanently off. The worst kind of
> =>rev
> =>> limiter there is. :-)
> =>>
> =>> You might be able to short the wire to ground permanently, for a crude
> =>> "fix", or with some creativity one could probably retrofit an
> =>earlier FPR
> =>> without too much difficulty. The rev limiter should be de-activated.
> =>>
> =>> Let me know if it works.
> =>>
> =>> Jonas
> =>>
> =>>
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Drew MacPherson - '84 Wolfsburg Edition Scirocco TurboDiesel