Is there any point to P&G in a diesel?

[Christ]

Originally Posted by Old Mechanic

My 37 Ford had a steering column lock.

Didn't know there was a car in the US where you could remove the key and not lock the column.

regards
Mech

There are some Chrysler and other cars that you can remove the key from the ignition while the engine is running.

Unless that was a seriously worn out lock cylinder...

RE: Radio locks - they're not a problem on most Fords. I don't know about other cars, but older Hondas can do it too... basically, anything that uses a 2 sided key and doesn't have a chip or resistor in the key.

The lock assembly is only moved by one side of the key. I'm not really sure why anyone made it a 2 sided key unless it was a matter of convenience, or so people would stop jamming keys in and breaking them off because they wanted to put them in upside down...

Now, have fun finding a shop that will correctly cut two keys on the same blank. I have a tooling shop that lets me cut my own keys, so I can get away with it. Not that I have any reason to do it right now.

[JacobAziza]

Originally Posted by Old Mechanic

Pulse and glide will improve you mileage, especially if you glide with engine off.
It takes a certain amount of HP to just spin the engine with no load.

Combine that with transmission gearing that allows lower RPM at highway speeds and the P&G window for better mileage closes considerably.

You may find it effective up to a certain speed but after than the benefits will become insignificant.

Another factor is the aerodynamics of your vehicle. Very high CDs will cost you a lot of your energy in wind resistance, expecially in a large frontal area high CD truck.

Bottom line, I would guess the P&G will probably help up to about 45 MPH. After that the aero drag will probably kill any benefit especially at peak speeds of 60 MPH and above.

regards
Mech

So, I have finally had the opportunity to drive on level suburban roads with a couple miles between stops.
Just going by an intuitive feel for the truck (no scangauge) I'm inclined to agree with you. The glides are more than twice the pulses, and it certainly isn't taking 2-3 times as much HP or fuel to accelerate as steady state.

Most of my driving has been dense city streets or freeway, and P&G was never practical, esp. considering anything below 25mph and I have to shift up, and anything above 40mph and my RPMs are excessively high due to no overdrive.
Seems P&G between 25 and 35 though is the sweet spot for this truck.
Of course, unless I find a route that I can maintain that for a hundred miles or so, I guess I'll never know just how much it helps.

[Christ]

I find that it helps some if you're going from a higher speed zone to a lower speed zone, to shut the engine off and coast down. I also find that (like you already do), shutting off and coasting to lights helps. If I know I have to go around a corner, I also shut down and slow without using the brakes as much as possible, then restart just after the corner, and accelerate back to reasonable speed.

So it might not really be P/G, but it's close, in that you're gliding down from speed, then reaccelerating.

[Frank Lee]

The Coupe needs a new clutch soon. My fe trend is sliding back down from the days I P&G'd a lot as I don't do it anymore. P&G DID accelerate clutch wear... the question is how much- insignificant or significant?

[Christ]

Sounds like a good time to transplant a certain Mazda engine/transmission...

[milesgallon.com]

I don't do P&G (at least not the continuous one) because I'm afraid the clutch wear will cost as much or more than the saved fuel. It's also not so nice to the other traffic if you're not alone on the road.

On the other hand I try to glide with engine on idle whenever it fits into the driving pattern, like down a hill I might glide even though I lose a little speed that has to be regained later and when comping to a stop in a crossing I try gliding instead of breaking.

In the case of down a hill I've been thinking about the standard gas saving recommendation to let the speed go down while going uphill and then regain speed when going downhill. If you apply pulse and glide to this scenario it might be more fuel efficient to gain speed while going uphill as then you'll get a really long glide downhill... any thoughts about this? Which one is more efficient?

[JacobAziza]

When I first started this thread, I was thinking only about level ground, no stops.
I always cut the engine for downhills or coming to stops.

I find on many hills I actually gain speed when coasting down, so then I just wait to drop down to my set speed on the way back up, then hold that speed to the next crest.

I suspect there are gonna be a lot of factors (specific vehicle weight and aerodynamics, steepness of hill, traffic flow) that will prevent any one method from being ideal.

[Christ]

I just don't accelerate on hills, as much as possible. I prefer to accelerate using the throttle on flats, or just using the weight of the car as much as possible on downhills.

Aside from that, I turn the engine off when it's not needed (to hold speed or accelerate), and almost never use the brakes, even in an auto. I make every attempt to determine whether or not I'll need to slow down more quickly than I can coast, and if I will, I leave the engine running so I can compression brake. Brake dust is harmful just as much as exhaust fumes, so it's a trade off.

[JacobAziza]

So, I think part of the problem for me before was I tried modified driving style before I started doing in actual mods.

So when I first tried P&G I had the open bed, no wheel skirts, no underbelly, no grill block.
I pretty much had the aerodynamics of a big old truck.

And I got a ratio of pulses to glides of 1:1 or worse. IE, it might take 7 seconds to accelerate from 50mph to 60mph, and then it would take all of 6 seconds to coast back down to 50.
So it seemed not that advantageous.

I finally tried it again post mod, and am getting closer to a 1:3 ratio - 5 seconds to accelerate from 45 to 55, and then 15 seconds to coast back down. So my engine spends more time off than on.
(It also doesn't hurt that I am more comfortable driving at low speeds now)
I did it for the last tank whenever I had much level highway driving to do, and it bumped my tank average up by around 2mpg compared to what I've been getting recently.

In conclusion, you all were right all along, but it seems to help a lot more the less wind resistance is a factor

[Pholostan]

Originally Posted by JacobAziza

I
My understanding is that the whole reason pulse and glide improves mpgs is because during acceleration the throttle plate is open, reducing the force needed to suck air past it, otherwise known as "pumping losses".

Sure, full throttle reduces pumping losses. The trouble is that all cars I've ever worked on don't lambda regulate full throttle. Usually they run a little rich on full throttle to be sure to avoid detonation. I think the rich mixture more than offsets the gain in pumping losses.

Disclaimer: I haven't worked on the newest cars from the last five years or so.