How to accelerate in P&G mode? - Page 2 - Fuelly Forums

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Old 06-05-2008, 06:14 AM   #11
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Quote:
Originally Posted by cugir321 View Post
I'm still trying to figure out P&G. Are you guys saying very light throttle in say, first, until I get close to 1.5 rpm's, then floor it until 2k, then shift, light throttle to 1.5, then floor it to 2k...etc.

I've been using light throttle always to 2k, then shift.
You seem to be under the impression that P&G is practiced when you might otherwise be normally accelerating from a stop. That is not correct. P&G is used when you'd otherwise be cruising at a steady speed.

Heavy throttle and lower RPMs (to result in the same amount of acceleration as light throttle and higher RPMs) is more efficient than the way you accelerate. Of course that only works if you've got a manual or a very obedient tiptronic/manumatic/etc transmission.

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Originally Posted by sonyhome View Post
For the fuel rate monitor, photos would be good, not just the taping of the injector, but overall what was done, the tapped wire needs to go back to the cabin.
Okay, I'll post some photos, but it's really really incredibly simple. Just run the wire to wherever your meter will be, and connect it to the meter's positive lead. Ground the negative lead to any ground (I use a power outlet) and enjoy.

Quote:
Also the tap gives you:
-duty cycle
- engine RPMs
The tap does not give you engine RPM, only fuel injector duty cycle.

Quote:
But you're missing speed to get MPG.

Therefore it'd be nice to tap another signal to get speed or tire rotations.
Vehicle Speed Sensor (VSS) is what you need to tap for that, and I recently read (and surely posted) about a DIY MPG gauge that uses VSS and the fuel injector tap.

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With that, we could do a cool ultra precise hypermiling analyzer.
If we could run this all (VSS, FI tap, and tach) into a computer or log it, you're damn right. That's a good idea. That's definitely a project that merely requires adding FI tap as an auxilliary input to a ELM327 interface. I have no idea how that would be done, it might have to be done through a separate serial port and combined in software.
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Old 06-05-2008, 07:04 AM   #12
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There are two different things going on here: accelerating, and cruising. For accelerating, use light throttle. For P&G where you would otherwise be cruising, use heavy throttle.

For accelerating, use first gear just to get moving. Go into 2nd gear at < 5mph, and from there use very light throttle up to a max of 2000 rpm before shifting, and keep shifting early as you gain speed. Use this to get up to, or nearly up to, your cruising speed.

Once you get up to speed, then start cycling between heavy throttle and neutral coasting - pulse and glide.
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Old 06-05-2008, 05:47 PM   #13
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Originally Posted by theholycow View Post
Okay, I'll post some photos, but it's really really incredibly simple. Just run the wire to wherever your meter will be, and connect it to the meter's positive lead. Ground the negative lead to any ground (I use a power outlet) and enjoy.
I put up a couple photos. I thought I had more. Anyway, take a look at the DIY fuel flow meter thread again. It's linked in my sig. Let me know if I can take pictures of anything else for you.
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Old 06-05-2008, 06:10 PM   #14
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[Off topic fuel meter]

Thanks! With that long a wire you still don't disrupt the ignition? Great, simple...

You do have RPMs with that tap, just not measured by your voltmeter. On a PC you'd see the frequency of the pulses, and the duration of on vs off (your duty cycle).

With VSS you have your speed.

With some software smarts, you have your knowledge of when you shift gears or coast...

That is definitively a project I'll want to do, including the software part.

I think using the audio input channel is the easiest. Can be done for injectors, but what about VSS? What kind of signal is it going to be? Gotta look around.
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Old 06-05-2008, 06:29 PM   #15
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P&G and acceleration.

So if I understand right, experience shows it's most efficient to use the following two modes?

A P&G mode: Shift from N into 4th or 5th gear and floor the accelerator with a led foot (or close to that at 80%). That uses WOT with low engine RPMs to accelerate the car.

B Red light mode: Accelerating from a stop, use light acceleration (feather foot on pedal), and shift early (say around 2000rpm) until you reach coasting speed.

C alternative to B?: For starting from a stop light, we could also do this: 1st, 2nd with light acceleration and a 2000RPM shift. Then skip 3rd, and go directly to 4th gear (or 5th?), and use a hard acceleration but with low RPMs. Is that what you guys are doing?

I suspect the trick is we need the RPMs for 4th gear to be at least the minimum bearable for the engine, so for starters, the RPMs must be at least 1200 when getting into 4th gear.


Automatic: For A/T cars the above seems hard to achieve. as a kickdown will downshift, and a semi hard acceleration will lazilly shift up.
So that should allow you to do (A) and (B), but harder to do (C), unless you have a good pedal feel and can hear when you're in top gear.

The difference between (A) and (B) mode in terms of the driver is that in P&G, he would depress the pedal more than when he accelerates from a red light...

Did I get it right?
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Old 06-05-2008, 08:31 PM   #16
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Look at a Brake Specific Fuel Consumption Map.

There is an area on the map that represents the most horsepower for the least fuel. I like to call it the "sweet spot".

The most basic and essential component of effective P&G is to understand that you try to stay in the "sweet spot".

The Sweet Spot is easy to determine even without special equipment.

Put your car in a gear that is higher than you would normally use. The Sweet Spot is the point where when you apply increasing amounts of throttle, you get almost no difference in acceleration.

It takes a very long time for my VX to accelerate from 1200 RPM to 2000 RPM in 5th gear, compared to using second or third gear, or even fourth gear.

Given the option by the traffic around you, use the highest gear at the lowest RPM for the pulse.

In some cases I actually have to downshift in order to accelerate more rapidly. After driving for 42 years, my shifting is second nature, including any rev matching. I don't look at any instruments, it's pretty much instinctive.

I have to stay within a minimum and maximum range of average speed to keep in time with traffic lights. When it works I can go through 26 lights without idling for 1 minute total time in a 20 mile drive.

This requires me to accelerate faster than I would if I had no lights or traffic to deal with. MY success at "adaptive P&G" is reflected in my mileage.

If I was on Route 17 north of Gloucester VA, where the road is 2 lanes, divided, with a 55 MPH speed limit and virtually no traffic, I could probably get close to 70 MPG, without EOC.

I read here that turning off the engine on a VX, causes the lean burn system to not work for 30 seconds after a restart. I may test this one day when I have time, and I am working on a very simple system for topping off my fuel tank in increments of less than a gallon, so I can make precise comparisons under identical situations without haveing to drive 250+ miles between fillups. That range of distance for me only uses about 40% of my tank capacity.

regards
gary
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Old 06-06-2008, 05:56 AM   #17
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Hypothesis: slow acceleration is always best (except in traffic light matching in Gary's case).

So I'm going back to old conventional wisdom that accelerating slowly is always best for the simple following reasoning: do you accelerate hard to get up to cruising speed when you don't want to P&G? Why, then, should accelerating hard for the purpose to glide afterward be any different?
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Old 06-06-2008, 06:18 AM   #18
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[Off topic fuel meter]

Should we take this over to the fuel meter thread?

Quote:
Originally Posted by sonyhome View Post
[Off topic fuel meter]

Thanks! With that long a wire you still don't disrupt the ignition? Great, simple...
The wire isn't connected to the ignition, it's connected to the fuel injector. Anyway, I too was concerned about disrupting the fuel injector, but my FE keeps going up and I'm not throwing any codes, so I it seems to have no ill effect.

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You do have RPMs with that tap, just not measured by your voltmeter. On a PC you'd see the frequency of the pulses, and the duration of on vs off (your duty cycle).
Careful with terminology. It's a dwell meter as used here. While you could get RPM data from it, why go to so much effort and do it the hard way when you can just get RPM the old fashioned way from the tachometer wire? Even easier if you're using a PC, use a $30 (on eBay) ELM327.

It probably won't work with your '93 Del Sol, though, unless that car is OBDII.

Quote:
With VSS you have your speed.
You'll get that with the ELM327 too. Since it's so cheap, that probably ought to be your starting point. I'm pretty sure there's open source software for it so you can write your own piece without rewriting everything.

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With some software smarts, you have your knowledge of when you shift gears or coast...
Again, th ELM327 will cover that too, with throttle position.

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That is definitively a project I'll want to do, including the software part.
Whichever way you do it, I'd like to be involved a little. I can't really write code unless it's simple, and I can't help with hardware due to geographical differences (unless you happen to live in the RI/MA/CT area).
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Old 06-06-2008, 06:27 AM   #19
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Quote:
Originally Posted by PaleMelanesian View Post
http://www.autospeed.com/cms/A_110216/article.html

High throttle, low rpm is best. Get the most efficient power out of the engine.

But... I'm finding that from a complete stop up to maybe 20mph, super light throttle ends up better. Then, when I'm closer to the desired speed, I switch into a heavy-throttle P&G routine.
But there's no power at low RPMS! But who am I to argue with a gas getter guru? But I am finding that I'm using less gas with light acceleration and slightly higher RPMs than with full throttle low as possible RPMs. We both have lean burn engines, too, so what's true for you should be true for me, right?
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Old 06-06-2008, 07:21 AM   #20
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Mine's not lean burn. You might actually have better results than I do with light acceleration. One more tool in your toolbox than in mine.

I'm not sure the exact dynamics of WHY slow acceleration works better from a stop, while hard acceleration works for P&G. But it does. For P&G, high throttle is unquestionably the best.

From a stop, for me in my car on my commute, harder acceleration will yield low 60's mpg, while feather-light acceleration will give me upper 60's and sometimes into the 70's.

(RIDE's advice differs from mine in part because he has LOTS of traffic lights to deal with, and I have relatively few. Also, he has lean burn and I don't.)
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