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Old 07-01-2010, 11:55 AM   #1 (permalink)
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ScanGauge II does not show open loop under DFCO?

Hi

my SGII does not show open loop (and hence not 0.0 l/100km) during DFCO. I can tell the vehicle does have DFCO ('99 Chrysler Grand Voyager, 2.4L 4speed AT), both "manually" by watching the tacho during decel, and by the XGauge O2-program as it shows 0 or 2 during DFCO, else it bounces around between 20-90.

Throttle position is 16-17 when I'm off the pedal, and the SGII DFCO threshold is at 24 (default).

Sometimes, if not always (not sure) when I lift off the throttle, the display shows OPEN LP and 0.0 LHK for a split second, before it goes back to CLSD LP and ~2-3 LHK. The O2 drops to ~0 and stays there.

It is always OPEN LP at full throttle accel.

Is there any way to "force" the SG to sense DFCO, or correct this in any way?
Or maybe my assumtion that the car does DFCO is wrong?

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Old 07-01-2010, 04:43 PM   #2 (permalink)
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Does it also report the vehicle as using fuel during this time? It might be that your assumption of DFCO is incorrect, but I don't know enough about the specific model to comment on that.
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Old 07-02-2010, 06:47 AM   #3 (permalink)
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Yes, it reports a fuel usage of ~2.5 l/100km at ~80 kmh (that's ~94 MPG at ~50 MPH).

From what I've heard, the fuel usage is calculated from air flow to the engine, so SGII will show a fuel usage even if the injectors are off, as long as it does not assume DFCO (from open loop and throttle closed). Is this correct, or have I misunderstood something?
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Old 07-02-2010, 09:39 AM   #4 (permalink)
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Pappnese -

My car does the same thing. I know this because I have a digital Air/Fuel Ratio gauge. I can "see" the 02 sensor go lean, but the scangauge is still reporting closed-loop.

My theory is that this behavior is OBDII compliant. The ECU/PCM initiated fuel cutoff and continues to report closed-loop operation because it is in full control, aka it knows *why* the 02 sensor is reporting a lean condition and that's ok. In fact, it's good because it's proof that the DFCO is functioning.

If you think about it, the other sensors might report values that are also tainted by DFCO, so why go into open-loop at all?

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Old 07-02-2010, 10:01 AM   #5 (permalink)
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this is an instance where some manufacturers will do something differently than others. What to report to the obd II port in this instance probably wasn't viewed as terribly critical or was otherwise ambiguous.
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Old 07-02-2010, 03:43 PM   #6 (permalink)
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You guys are probably right, that my car does DFCO, but doesn't report open loop when it does.

Any workaround to get the ScanGauge to report 0 fuel usage while DFCO then? Or is this impossible, or maybe we have to wait for an firmware upgrade?
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Old 09-06-2010, 04:47 AM   #7 (permalink)
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Have you tried setting the SGII DFCO threshold to 18?

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