Most fuel efficient speed?

I think what you all are missing on the injector cutoff/auto tranny thing is that in order for the injector cut off to work while keeping the engine turning, is that the TC has to be in lock-up. Without the TC being locked up, cutting the injectors would stop the engine from spinning since there is nothing to keep it turning.

 

Even with the TC being in lockup, the transmission would still be in drive, which has no over-run sprag to allow the power from the wheels to travel through the transmission and drive the engine speed. The thought process that I am looking into would be if when it selects DFCO, that the TCC is in lockup, and the computer activates a solenoid in the transmission that engages a sprag clutch. I don't have enough information gathered yet to give any indication for sure.

 

Just drove 650 miles one way to Florida and back, averaged 19.9 mpg's down and back running 75+ mph. 90% of the time was on cruise control.

 

man
I can't understand how you guys are getting such good mileage. Mine sucks...getting under 16 mpg...'05 trd OR access cab with a K&N CAI with AFE pro dry (cleaned recently) 245/75/16 snow tires on now, trd exhaust.
I've cleaned my throttle body, so what's killing my mileage?

 

Interesting

I get a bit better than that with my DCLB 4x4 , OME lift , LT275/70/17 tires , Leer commercial cap and 300 lbs of tools

 

Not sure with automatic but with stick it is as low as 1000-1200 rpm and will work even on flat pavement.

If I let off the gas in 5th at say 2000 rpm and coast in gear there is no fuel use until around 1100 rpm, at which point there is a clear surge as the engine gets fuel and starts to run again.

 

not "interesting" at all! it sucks!
(I'm also running a leer cap)
love my truck, but she's got a drinking problem. My buddy's full size F-150 V8 with high rise cap gets better mileage than I get!

 

Damn man! I average 16-17 mpg city and hwy with factory exhaust and intake, running 255/85/16's and 4.88 gears. When I still had the 3.73's I averaged 18-19. Got 22 on my trip to Moab doing 65 mph with the 3.73's and I had a ton of gear in the cab and bed.

 

Further research has revealed that the DFCO is engaged for a short time....a VERY short time. When engine RPM drops below a predetermined RPM (Between 800-1200 RPM depending on the vehicle) the injectors will fire again to prevent engine stall. So it is a short term condition that may only last for less than 20 seconds or so each time.

 

But if you say made it through the Eisenhower tunnel heading to Denver and have miles and miles of steep downhill you can DFCO for 10 minutes or more. It may kick back on at low injection rate if the engine cools down enough.

 

I posted this awhile back while discussing DFCO

The injectors will briefly pulse the injectors enough to produce heat.

http://www.autoshop101.com/forms/h43.pdf


cutoffgraph by worthywads, on Flickr


fuelcutofftext by worthywads, on Flickr

 

I did a little bit of un-scientific testing on my last 2 tanks of fuel. I have a 6 speed 2010 DCSB OR with 265/75-16's. First tank I shifted consistently between 1500 and 1800 RPM. Nice and easy. It gave me about 18.5 mpg. On the second tank, I shifted between 2500 and 3000 RPM consistently. On the second tank I was at 17.5 mpg.
The thought was that if you get to cruising speed quicker, you would spend more time there. But, as I thought, lower rpm all around seems to be the better answer.

 

You can still give it decent throttle while you are short shifting below 2000 rpm and still get good results, you don't have to baby the throttle.

 

http://ecomodder.com/forum/showthread.php/speed-vs-mpg-charts-post-em-if-you-15182.html

 

The only answer is don't drive it like you stole it.

 

Often done with a clutch pack either internal to the TC or the trans. If the lockup stays on (early 700R4 GM's did this) the engine will stall same as stopping in gear with a manual with out the clutch depressed because the forward clutch pack is still applied even stopped.

 

1500-1800 rpm shifting? I granny shift mine into 5th gear at 12mph and fuel ecomony is good. Don't rev the thing; its a truck not a Bugatti Veyron.

A steady 52 mph gets EXCELLENT highway economy in my experience.

Changing the rear diff oil to synthetic helped fuel economy alot.

 

Just fyi, there is a single clutch piston in the TCC, not a pack, but that is probably just symantics.

Yes, lockup would cause an engine stall on certain older model automatic transmissions (including the 700R4 and the 4L60/4L60E that came after the 700) HOWEVER, you have to look at the whole picture. There is a one way sprag in each of these that allows freewheeling in one direction, and load in the other. AGAIN this will not allow the rotational power from the wheel to drive the engine, but it will allow the opposite, where the engine will stall out if TCC is engaged. You have to understand the internals of a transmission and how it operates. Like I said, if the TCC is engaged, AND the transmission was designed to engage a clutch pack that controls the one way sprag (which happens in most vehicles if you select "L" or "2" on the shifter) then you could drive the engine from the wheels. The problem comes with trying to get all of that timed just right. If the engine rpm dropped too low before the engagement was selected, then you would lose pump pressure, and it would all be a moot point then. Also, if you engage the sprag, and the TCC, you would have a direct engagement from wheels to engine, and it would act similar to a manual transmission. If you take your foot off the gas pedal on a manual in say 5th gear, you will slow down pretty fast. This drop in speed would defeat the advantage of using DFCO in the manner that was earlier described. Hence the research showing that it is a very short time that the DFCO is actually active (seconds mostly)

 

I still say that average RPM is much more relevant than speed in regard to MPG. If you can never go over 2500RPM and try to keep it under 2000 during most driving, you're gonna see your MPG increase. Gain momentum while approaching hills and descending hills, try to never need your brakes, anticipate speed zone changes and traffic control devices and generally drive like there is an egg between your foot and the gas pedal that you don't want to break.

Of course, NONE of this makes driving exciting and you're still driving a PU that will top out in the mid 20's.