MetroMPG mailbag: how to keep SG live when engine off?

[MetroMPG]

Received this question from a metrompg.com visitor:

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).

[MetroMPG]

Hmm - seems like the UltraGauge doesn't like the engine-off technique in some cars...

Originally Posted by California98Civic

My UG won't give me avg mph because the EOC routine messes up the data

Do you have a kill switch, or are you using the key?

Keying off the ignition screws up the ScanGauge readings in my Firefly - but adding a kill switch fixed the problem.

MetroMPG mailbag: how to keep SG live when engine off?

[California98Civic]

Originally Posted by MetroMPG

Do you have a kill switch, or are you using the key?

I installed an injector kill switch with a friend. It cuts-off the ground. When I time it right, the UG does not even go black temporarily. But it has always been the case that in the "run" position, with the injectors off, the speed average starts climbing steadily, almost as if it is calculating distance traveled in some unknown metric.

[MetroMPG]

That's odd. Seems to be a UG glitch then. Thanks for clarifying.

[tinduck]

Originally Posted by MetroMPG

Received this question from a metrompg.com visitor:

1. Set the ScanGauge fuel type to "Hybrid" - in this mode the unit stays active when the engine stops but the ignition remains

Hi MetroMPG,

I have the same problem but with a diesel... When stopping the engine at traffic lights ScanGaugeII shuts down after a few seconds.

But for a diesel engine the hybrid setting probably will not work.

Or will it?

So long,

Tinduck

[MetroMPG]

I suspect there is special code in the "diesel" setting that you need to use for best accuracy.

ScanGauge needs a new category soon: diesel hybrid.

That would solve your problem.

[PaleMelanesian]

Look in advanced settings for "Sleep event". That's a new option on the latest models. Default is 0 rpm, but the other choice is NO COMM. That might do what you need.