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Old 08-14-2017, 02:00 AM   #11 (permalink)
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Originally Posted by oldtamiyaphile View Post
Remember, a OBD gauge is never going to be accurate to within 2%. The biggest thing that will throw it out is a change of driving style.

Pulse and DFCO doesn't work, even on cars like my Trafic (tiny diesel- heavy vehicle) where I can't even tell if I'm gliding in gear or neutral.

Pulse and gentle throttle may work. It works for Hybrids and it works for diesels, but I have feeling for a typical petrol car it may not - you're operating at max pumping losses that way - which is contrary to the whole point of P&G.

I don't bother with P&G on the highway - you'll have the same results just sitting in the slow lane.
I know my ScanGauge does not give me a definitive mpg but it does show me if what I am doing is better than worse than what I was doing before.
I was on the highway yesterday evening and what I am doing is more Pulse and Gentle throttle than using DFCO. I can get 50 seconds at 100+ mpg for 10 seconds at 40 mpg and when conditions allow (like slight down grades) I sometimes can use full DFCO.
And here in Scotland our highways are either one lane in each direction or two lane, where the "slow lane" is travelling at 50 - 55 mph and the "fast lane" at 60 - 65 mph. Unless of course it is a blanket 40 mph with average speed cameras!

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Old 08-14-2017, 11:01 AM   #12 (permalink)
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SentraSE-R did some quite in depth data collection to find how to get the most out of P&G with his car.

With his car 70% load during the pulse, and engine off during coast is needed to break even vs constant average speed of his P&G. He had a 3:1 glide to pulse ratio.


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Old 08-14-2017, 11:55 AM   #13 (permalink)
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So anything other than engine off pulse and glide is just a waste of time (and petrol). Well as I don't do engine off I won't bother with pulse and glide.
I'll settle for anticipation and driving without brakes.
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Old 08-14-2017, 01:12 PM   #14 (permalink)
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Limited example size of only 1 car, your mileage may vary.

My input was only as to how much does P&G gain over just driving the average speed and is it worth the effort.

It can be significant if you done correctly, not if you don't.

Serious P&G do it regardless of grade, doing only when the gravity is in you favor edges the advantage towards your style working.

I use DFCO when gravities helping which isn't often here, other wise just N coasting to stops and driving without brakes.

Last edited by roosterk0031; 08-14-2017 at 01:24 PM..
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Old 08-14-2017, 01:19 PM   #15 (permalink)
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Old 08-14-2017, 08:40 PM   #16 (permalink)
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Quote:
Originally Posted by JockoT View Post
I know my ScanGauge does not give me a definitive mpg but it does show me if what I am doing is better than worse than what I was doing before.
Not really. When you calibrate your OBD gauge, you're basically telling it 'here is my fuel consumption for the average engine speed/load over the last tank'.

I've had my SG2 for around six years and I don't think I've ever had the calibration be within 2% on consecutive tanks - it's quite typical to be out by +/-5% (ie a 10% error spread). Highway drivers will have a smaller discrepancy because they're average speed/load is more consistent. But when you change driving style you throw calibration out the window to a large extent.

When you accelerate, your AFR turns slightly rich (acceleration enrichment), even if you car stays in closed loop, the only way to accelerate is to run slightly rich. This is almost certainly enough to counter the 2% gain the SG reports.

The SG2 is broadly useful in many respects, but it falls down on really fine tuning driving style. I use the onboard display for IC in my Renault as it does account for the AFR, and the SG2's short trip as an indicative game.

I just fitted an MPGuino - that does measure fuel and therefore enrichment - to my Proton. I'll try Pulse and DFCO while I zero in on it's ideal driving style, but from memory when I last used it, I don't think it was accurate tank to tank to within 2% either.

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