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Old 08-05-2008, 11:04 AM   #1 (permalink)
MetroMPG
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Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,193

Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 53.56 mpg (US)

Winter beater Metro - '00 Chevrolet Metro
90 day: 61.98 mpg (US)

Fancy Metro - '14 Mitsubishi Mirage top spec
90 day: 58.72 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 70.75 mpg (US)
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MetroMPG mailbag: how to keep SG live when engine off?

Received this question from a metrompg.com visitor:

Quote:
I have the Scanguage unit and would like to try your method of shutting off the engine but I would like to keep the guage on. How did you get it to stay on for your tests? Also, does it really make sense for me to do this if i have an automatic transmission?
1. Set the ScanGauge fuel type to "Hybrid" - in this mode the unit stays active when the engine stops but the ignition remains on.

2. I don't know if you have a Metro. If you do, then one of the problems you've discovered is that even if you key off briefly and immediately back on again, the SG takes more than a couple of seconds to re-initialize. (I think it may even stop registering distance traveled until the engine restarts - could be wrong there; it's been a while).

The issue is the Metro's "ISO" OBDII communication protocol. (There are other protocols which don't have this problem.)

The solution is to use an engine kill switch, so the ignition key remains "ON" while you stop the engine and power to the SG is uninterrupted. An alternative might be to wire 12v to power the unit independently of the OBDII port, but I haven't tried that.

3. It's OK to shut off the engine in any automatic when you're stopped. But you could potentially damage it if you coast with the engine off, unless the manufacturer specifically says the transmission is designed for "flat towing" (engine off, in neutral, 4 wheels on the ground).

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