[s-cars] Engine Cutout

[Kirby Smith]

Well, _if_ the tach signal were derived from the ECU's generation of
spark timing signals, then there would be more of them for a V8 per rev
(3) then for an I5 (2.5).  The V8 tach would be expecting 3 per rev and
thereby read low when used with the I5.

kirby

Bob Rossato wrote:
>
> This is now the 3rd car, including mine, that I've heard about with this
> problem.  If you're having the same problem as me, your tach is reading low
> by ~17% and you have actually reached the 7200 rpm redline.  Check your RPMs
> vs. speed.
> Here are some calculated RPMs vs. speed for 3rd, 4th, & 5th.
>
>                      MPH
> RPM     3rd        4th       5th
> 2000     29.3      38.7     49.3
> 2500     36.6      48.4     61.6
> 3000     43.9      58.0     74.0
> 3500     51.2      67.7     86.3
> 4000     58.5      77.4     98.6
> 4500     65.8      87.1     110.9
>
> You can also rev the engine in neutral to rule out whether it is a
> detonation problem but you'll find it hits the same 6000 rpm wall.  I also
> swapped ECUs with a local lister with no change.  In the end I found out
> that the problem is with the circuit board in the Instrument Cluster.  I had
> obtained a spare IC for the purposes of swapping the tachometer, however, my
> IC with the other tach had the same problem and the other IC with my tach
> would rev all the way to 7200rpm.  Unfortunately, the other IC is metric so
> I'm still running my IC and living with the problem for now.
>
> Check your IC and I think you'll find evidence that the circuit board has
> been replaced.  On mine there was a part number label that was applied
> across the interfaces of the back cover and front housing so it was torn in
> order to separate the back cover.  I'm thinking that our cars must have had
> warranty work done on them for some problem on the IC and they used a V6
> circuit board in the replacement.  Don't know why that would make a
> difference since the signal is coming from the crankshaft RPM sensor, not a
> spark plug, but coincidently 5 is 17% lower than 6.
>
> Bob
>
> > -----Original Message-----
> > From: s-car-list-admin at audifans.com
> > [mailto:s-car-list-admin at audifans.com]On Behalf Of Andrew Pennell
> > Sent: Monday, October 21, 2002 9:25 PM
> > To: s-car-list at audifans.com
> > Subject: [s-cars] Engine Cutout
> >
> >
> > I have a 95 S6 Avant. At approx 6000RPM the engine will act as if it
> > hit the redline. No ECU faults and the engine is otherwise running
> > well. Any ideas? It seemed odd that it would cut out at that speed. I
> > was only aware of the redline and "limp home" condition that would
> > cause engine or fuel cutout.
> >
> > -AP
>
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