[Gmecm] Ignition off fan

[Robin Handley]

Aaah. Thanks again, Scott! :-) I see how, from the circuit diagram, when
ignition power is lost, the high speed fan relay drops off.

So, since my fan goes straight off when I turn the ignition off, would I be
right in deducing that the $58 code goes through all the motions of
controlling 2 fans, but the code for the 2nd (high) one achieves nothing on
the 749 h/w, but _does_ work on my 727 h/w? :-)

If this is right, then it's probably worth me trying to find the #1 fan pin,
to get the ignition off running. Shame there seems to be no cross reference
for this! I guess I just check the quad driver pins...

Robin

BTW: I'm also observing my fan flicking on then straight off a few times as
the engine temperature rises to the high fan ON temperature that I've set.
The CTS is a little noisy (mostly +/- 1 C, with occasional dips of 6C !);
but, looking at the plots of CTS vs. fan ON, there isn't a 100% correlation
between the CTS spikes and the fan state transition. I'm still trying to
understand the code (not helped by not knowing what half of the zero page
locations, particularly statuses, mean), but I've been wondering whether the
$58's high fan control logic isn't as sophisticated as that for the control
of the low fan (i.e. high fan has no delayed start up - which might reduce
the likelihood of the 'flicking'). If the $58 only ran on h/w that didn't
use the high fan logic, then GM may never have noticed this behaviour, or
didn't care(?)

Having said this, I'd expect the natural hysteresis of the ON/OFF thresholds
to avoid this kind of 'flicking' problem...

I also plan to look at my CTS wiring. I 'cheated' by wiring the GND side to
chassis. This massively added to the CTS noise when I had had bad engine
grounding (now fixed), but still may be adding some. I'd be interested to
see others's CTS plots to compare noise.

----- Original Message -----
From: "Scott Peitzsch" <jlg-sep at comcast.net>
To: <gmecm at diy-efi.org>
Sent: 28 June 2006 12:25
Subject: Re: [Gmecm] Ignition off fan


> I did a poor job answering the question first time around.  The code does
> support two fans, but the hardware does not.  The turbo Sunbird does
> indeed have only one cooling fan as shown here:
>
> ftp://ftp.diy-efi.org/pub/gmecm/manuals/1227749/749sunbird3.jpg
>
> It runs in full speed mode when the ignition is on, and in slow speed
> mode when its off to reduce current draw on the battery during the
> fan run-on period.
>
> -Scott
>
> ----- Original Message -----
> From: "Robin Handley" <Robin at FuryWorld.fsnet.co.uk>
> To: <gmecm at diy-efi.org>
> Sent: Wednesday, June 28, 2006 4:38 AM
> Subject: Re: [Gmecm] Ignition off fan
>
>
> > Thanks Scott, although I'm confused. The $58 code has lookup values for
> > two
> > fans, so I had assumed that the Sunbird and/or Sy/Ty had two fans. Am I
> > wrong? Since I have proved that the high fan temperatures drive my fan,
it
> > would be weird if the low fan temperatures weren't used for something...
> > What am I missing?
> >
> > Robin