Re: L-Jetronic ECU fragility? was V6 stalling - slightly off, now with even more off!

[George Graves <gmgraves@xxxxxxxxxxx>]

I think you misunderstood, or perhaps I failed to explain well enough.

My point was that the G-Tech Pro used the ignition noise on the car's 
12 volt power "supply" to sense engine RPMs. The fact that it does a 
reasonable job is merely illustrated by the fact the that the G-Tech 
Pro's internal LCD 'tach' (just a bar that moves across the screen 
which has numbers above it) seems to track the one in the car pretty 
accurately. Of course neither is real accurate and the "calibration" is 
ball-park at best, but the electronic tach in my Alfa Romeo is actually 
connected to something other than just 12 volts for it's RPM 
information, yet the G-Tech Pro is able to get more or less the same 
info from just the noise on the car's DC supply. I don't think that 
accuracy is at all that important in a tach. After all, the indicator's 
position on the scale is much more important than the actual numbers.

George Graves
'86 GTV-6 3.0S


On Friday, June 20, 2003, at 05:12 AM, alfa-digest wrote:


> Date: Thu, 19 Jun 2003 21:31:00 -0700
> From: Jon Pike <jhpike@domain.elided>
> Subject: L-Jetronic ECU fragility?  was V6 stalling  - slightly off, 
> now with even more off!
>
>
> > While this is, as you say, a bad thing, an interesting aside (which
> > backs-up what you say about the system being poor at suppressing
> > transients) is the fact that the G-Tech Pro performance meters all get
> > their RPM tach information out of the same cigar lighter jack as they
> > get their power! They tell the operator to rev the engine first to 
> > 3500
> > RPM and hold it, then press the "OK" button, then let the RPMs drop to
> > 1700 and press the "OK" button again. The computer obviously 
> > integrates
> > the noise spikes on the line to read RPMs. It works too. My G-Tech Pro
> > Competition model's digital tach tracks my GTV-6's tach very 
> > accurately!
> Hmmmm.... the electronics guy in me is jumping up and down at the idea
> of a device designed to calibrate itself to the likely inaccurate tach
> on the dashboard, when it probably has a more accurate clock inside to
> count against!
>
> Heck, you could then use it to check your tach's accuracy,  rather than
> the other way around..  but that's me..
>
> Uh,  Alfa's rule!!!  (Alfa content)
>
> Jon and Marcia
> Irvine,  CA
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