Two (2) P&G questions

Discussion in 'Start Your Journey Here' started by Dougmeister, Jul 30, 2008.

  1. Dougmeister

    Dougmeister Member

    1) Does "Pulse & Glide" by definition mean:

    a) not depressing the accelerator
    b) putting the vehicle into neutral
    c) putting the vehicle into neutral AND turning the engine off?

    Last edited: Jul 30, 2008
  2. sandman

    sandman Active Member

    I am just learning about P&G myself but those methods you mentioned are all ways to Glide. I would say the definition of P&G would be you pulse up to a certain speed then glide to a lower speed. To make it simple you have a set speed lets say 35mph, you then would Pulse up to 40mph then glide down to 30mph and repeat.. Here is the hard part learning the best way to pulse and best way to glide to obtain best MPG..
  3. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    (a) is not really a glide. It's engine-braking.
    (b) and (c) are both glides. (c) will give better mileage, but it's not for everyone, or every car, or every situation. Use with discretion.

    Sandman - that's the basic idea. 30-40 P&G will give pretty good results. That's a very useful range.

    Try to adjust to the conditions, always trying to maximize the glide. That's where the magic happens.
  4. phoebeisis

    phoebeisis Well-Known Member

    With some vehicles there isn't any perceptible engine braking despite being an AT and leaving it in D rather than N. This holds in my 98 Suburban down to about 23-25 mph where I can finally feel a downshift and a bit of engine braking.

    I can't think of any good reason to not put a MT in N. With ATs there is a good reason to leave it in D (especially if they have been designed to not provide engine braking). The reason is that occasionally folks have accidently slipped it into R while trying to bump it into N. Some ATs also aren't flat towable ,and that changes how you should P&G.

    Many AT owners choose to P&G lite- just leaving it in drive and lifting off the pedal. Of course, turning off the motor will give better FE - no question about that.

    Start slowly and if you decide to motor off glide practice it on deserted roads, low speeds low stress situations. Turning the key to shut the motor off while moving just isn't "natural" and it takes practice.Initially Practice all the motions while stopped. Run thru them in your mind-dry runs. Make a 1-2-3-4 checklist.

  5. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    Interesting. In my Odyssey, it's very happy to hold it in gear and brake away, and then at around 25mph it lets go and drops to idle. Just the opposite of yours.
  6. phoebeisis

    phoebeisis Well-Known Member

    Pale- I got a "reason why" from someone here I think. Apparently GM set it up to freewheel intentionally. The explanation was that the fluidpump/torque converter is depressurized- some sort of bypass I think?? Bottom line the wheels can't transfer power/torque back to the engine. I suspect there is even more to it than that-my memory is a bit vague on it.

    I literally can't tell the difference between lifting the throttle in D or lifting and placing it in N ! Kinda strange , but I don't feel any engine braking until about 23-25 mph where I feel a distinct downshift. Even then there isn't a heck of a lot of engine braking.

    GM knows how to get FE from their FSPs -well relative FE.

    I seem to recall that our 2003 Pilot had a lot more engine braking in 5th than this Suburban-which has just about zero in 4th.

    The minivans-Odyssey/Sienna obviously were designed with wind tunnel or virtual wind tunnel help. Heck, they look an awful lot like our Prius. Your Odyssey has a good 5 mpg HY advantage over the Suburbans ,and I would bet most of it is the shape. They-minivans -have the interior volume of a Tahoe/Yukon with a huge mpg advantage. If I had the $$ a used 2002-2004 Odyssey ($7000-$12000 with under 100,000 miles) would be really tempting as a haul everything and trip vehicle.

    Can the Odyssey carry 4x8 building material with the hatch closed? Our Pilot had about 78" front to back length with the seats down? I'm guessing thwe Odyssey is about 90" ,so it might just be able to carry 4x8' if you didn't mind ducking your head and propping it on the front seat back?


    PS -Big aside -a 2003 Suburban-64000 miles loaded with everything most of which I really don't need except for the power drivers seat -sold for under $9950 on Ebay yesterday. This is the cheapest price for a loaded low mile one I have seen.The slight drop in gas prices might cause a little blip in used sales- but not much. The 2003 would have sold for $40,000 plus 5 years ago new.Now it is worth just 25% of selling price,so the guy who traded it in got maybe $6000 for it-15% of what he paid.He paid $6000 per 10,000 miles!
  7. ksstathead

    ksstathead Moderator

    I submit that anytime the pistons are moving, energy is consumed and some engine braking is occurring. When you 'feel' the braking, that means the tranny has downshifted and even more energy is consumed to speed up those pistons.

    Either way, your coast in D will be shorter than a glide in N. I coast in D quite often, but it is not a glide.
  8. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    I haven't done it, but I believe the Ody will hold plywood flat on the floor. You have to remove the 2nd row seats. They don't just fold down, but they are designed to be removable. Fold the back down, flip the lever, tilt forward and lift out.

    I've seen that same free-wheeling action in other GM autos. It's great.
    Last edited: Jul 30, 2008
  9. Dougmeister

    Dougmeister Member

    Thanks, all ;-)
    Last edited: Jul 30, 2008
  10. TahoeMan

    TahoeMan Life in the tall lane

    Hey phoebeisis,

    My 1996 Tahoe behaves similarly in "coast" mode to your Suburban. I put in a new tranny @ 110,000 miles in 2004, and it seems to coast more than did the original before engine braking is perceived (or downshifting on braking). It seems this may be an intentional adjustment on the AT by GM.

    I've noticed reasonable MPG improvement (IMO) just doing the engine on pulse and coast.

  11. phoebeisis

    phoebeisis Well-Known Member

    Tahoeman- Gm always has updates that the trans get when they are rebuilt by a reputable rebuilder. I wouldn't be surprised to find out that the updates improve FE.

    ksstathead - no my coast in D is just as far as my coast in N. The downshift I feel is the transmission re engaging and them downshifting.

    I wouldn't be surprised to find out that when you lift completely off the throttle in top gear the transmission and electronic controls do exactly the same thing they do when it is in N. I have timed and measured the glide ,and watched the scangauge. I have also- obviously- bumped it into N after gliding in D- THERE IS ABSOLUTELY NOTHING you can "feel" when you put it in N- nothing!! The SG also shows the same MPL and LPH in D and N- no difference !!

    The control unit must have hard wired instructions to re engage at 24-25 mph or so.

    The pistons are moving because the engine is on and fuel is being used-slightly more than standing idle fuel-about 3 lph vs 2.6 lph at standing idle.

    The GM FSPs are absolutely perfect for P&G motor on or motor off and they respond very well to increased tire pressure. Using 2.6 lt per hour they also respond well to shutting off at redlights (once warmed up- they don't really give a shut off dividend until warmed up- maybe 5 minutes of running on hot days).

    GMs spent some time getting decent FE from them; they did/do really lag in respect to aero drag. If they plopped a scaled up Odyssey skin( or better yet a Prius skin) on them,and panned in the bottom they would get 3-4 mpg better hy.The CDs of the latest vintage big SUVs are probably about .4 or higher- my 1998 is about .45 (a slightly rounded brick).

    I would love to get my hands on a 2007 bodied Sub/Tahoe-they are rated 3 mpg hy and 2 mpg city better than mine( 14/20 vs 12/17). I suspect it is a 25 mpg hy vehicle,and might have 27-28 mpg hidden in it. City it is big and heavy- hard to get around that -other than P&G or maybe cobbling together an electric motor assist for city acceleration.( it could be run by a chain and sprocket attached directly to the driveshaft -and set to freewheel, of course))



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