Forcing an *up*shift in an automatic--mpgs

What you want to do will damage the engine and tranny 'and' drink gas.

Your idiot light gas meter lies. Your tranny shift is correct.

Real life says if the engine is kept in the sweet spot, the mileage is the best.

In our Jeep 5 speeds with larger than stock tires, and this works for all that I know have tried it, if we keep our engines in the 2300 rpm sweet spot that they seem to like, I for one get 23 mpg highway pretty consistently.

If however we run one gear up all the time which drops the revs to say

1700 at 65 mph, our, mine in particular, gas mileage drops to about 18 mpg.

This works the same off road running trails.

We 'do' however need what you want, a downshift limiter on the automatics. This can be done electronically on the newer Chrysler Jeep autos, don't know about others.

We need it for hill climbing. The autos do fine about 2/3 the way up steep stuff in 2nd, but then they want to jump to 1st. This just spins tires and they are stopped, digging holes.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > Awl--

Mike Romain wrote in news:465c6a34$0$18887$ snipped-for-privacy@unlimited.newshosting.com:

Don't know about now, but years ago (when gas was more expensive than now in real terms), fuel economy "races" were common.

It was discovered during these runs that lugging the engine (as in shifting way early and then flooring the gas pedal) did in fact return the best gas mileage.

But that was with carbureted cars. I don't know if FI engines would respond the same way.

Still works the same. The reason behind it is that when the throttle is wide open there's no losses due to the throttle valve. When it's nearly closed, the engine has considerable pumping losses.

cu .\\arc

This is so totally dependent on the type of vehicle that without that information there is no meaningful repsonse.

In older automatic transmissions shift points are controlled 100% by mechanical, vacuum and hydraulic methods. The only "computer" is the hydraulic valve body plus a mechanical governor and a vacuum modulator and/or throttle valve. A limited amount could be done to such a transmission by tampering with the governor springs, valve body, throttle valve cable -- or rod -- is so equiped, or installing an adjustable vacuum modulator.

On the other hand, my 96 Ford 3/4 ton Powerstroke diesel has a hydraulic valve body that controls shift FIRMNESS only. Shift points are determined 100% by the power control module. Ford has used several different shift strategies for 94-97 Ford Powerstrokes and a change of computer or computer re-flash will change shift points. I went one step further and got a chip with custom programming. I realized an enormous power increase from the chip and my oversize injectors. I sent the chip back for further programming to prevent constant donwshifts from overdrive on the slightest hill -- downshifts that were totally superfluous with the increased torque from the engine. I also told the programmer that I wanted it to hit OD at light throttle at 50 MPH instead of waiting till 60. I wanted the torque convertor to lock up at about 38 mph instead of 45 mph,. I wanted no downshifts until the engine was seriously lugging or I pushed the (fly-by-wire) accelerator to the floor. He told me "no problem" and to just send the chip back if I wanted further tweaking. I heard on the Ford diesel forum that I frequent that, against his better judgment, he programmed a chip for one guy that locked up the torque convertor at 20 mph! Wasn't a good idea and the owner of the truck thought better of it and sent it back to be re-flashed.

I have no idea what you are driving so no idea what might be possible.

Don

Damn, man, I sure wished my carbureted Jeep new about those tests.....

I have tall gears and when I use overdrive or 5th gear, I still have power to pull so it isn't 'totally' lugging the engine, but my gas mileage drops at least 5 mpg when I use it....

The places we go camping are 200 miles away so I have lots of chance to try different things out for mileage on the same 200 mile track.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 (More Off Road album links at bottom of the view page)

innews:465c6a34$0$18887$ snipped-for-privacy@unlimited.newshosting.com:

The same thing is true. Further, the danger with lugging is that the carbureted engine would buck, which was hard on the driveline. Further, modern bearing materials and lubricants further reduce damage from high bearing pressures. Today, as long as the engine will still accelerate smoothly, things are okay. One of the European mfgs did a test on this after the first oil embargo, and verified no excessive engine wear from lugging.

My new Chrysler mini-van has the shift points too high for good fuel economy. The sweet spot for throttle opening is about half to three quarters open for most engines, BUT, the rpm should be as low as possible. So in my stick shift car I can short shift and get great economy, but the van is auto and is obviously set at a peformance shift point setting. I'd LOVE to find a way to lower shift points. I have tried backing off slightly at an rpm I'd like to shift at, but can't force the upshift. I can force the upshift a bit by backing off, but at an rpm much higher than I would shift a stick at.

Very interesting.

My vehicles are a 04 Nissan Frontier, and an 07 Honda Fit--neither performance vehicles.

The idea of getting custom programmed chips is neat. How do you go about doing this? Can you do this yourself, with software, etc.? It might solve the problem, even if the new set point is a little high, as it's always easy to downshift.

Even if the setpoints are chip-controlled, tho, ultimately the chip is just sending out a voltage to trigger some event. Is it possible to intercept/supply those voltages to control the shifting? Are multiple events being addressed simultaneously?

I'm too lazy to look it up, but I think it was an old PopSci or C&D something where they were talking about this or doing a fuel economy test or something, but an IC engine is most efficient around 80% throttle and as low revs as possible.

It is one of those "all other factors being equal" things...

FWIW, on my old Jimmy with taller than stock tires, I got better mileage in 4th and mid-throttle than 5th and 90%/full throttle...

theory reality.

I keep track of the mileage in my Trans Am (5.7 V8), Beretta (3.1 V6) and Subaru (2.5L F4) and they all average within 19-22 mpg combined driving. At 100km/h, the Subaru is turning around 2600 rpm, and the TA is turning about 1100 in 6th and probably getting better fuel economy...

Ray

innews:465c6a34$0$18887$ snipped-for-privacy@unlimited.newshosting.com:

These late shift points have always bothered me. I recall when most automatics shifted early and used the engine torque to keep things moving. But even with big engines it seems like the manufacturers started moving their shift points to higher and higher rpm's in the

70's. It would probably mess up the emissions certification but I sure wish the manufacturers let you plug in a "code reader" and set your shift points however you wanted them within some reasonable limits to avoid damage.

This solution has been around for a while. We call it a MANUAL transmission.

Ray

It wasn't 80% throttle, but the engine at 80% of output. This means to use this method, the engine has to be undersized so it can run at 80% of full load during cruising. Then, of course, there is little reserve power, which is why this isn't done, except in hybrids.

I remember the Popsci article pretty well- it was a full-size, lightened, chain-drive pickup truck with no glass. A smaller engine had been put in, I think. It was green, or was it blue? He also would accellerate at 80% power, then kill the engine and coast.

Dave

It WAS around for awhile. Try getting a mini-van with stick shift today. Unavailable!

Thankfully they are still available on subcompacts, but the stick shift is, unfortunately, on its way out :-(

That's a different article than the one I had. The two articles I'm thinking of, one was in C&D where they ran a MPG "race" and used a Suburban as a wind-break, and the other was just a discussion of HP/Torque curves and how it related to fuel economy - basically engine dyno fuel consumption stuff. If I didn't have about 5,000 car magazines I'd know where it was...

I know. One of the reasons we bought the Subie was because of that. You can't even barely buy a pickup truck with a stick anymore.

Ray

01 Trans Am (6 speed manual) 02 Subaru Legacy (5 speed manual) 90 Chev 1/2 Ton (5 speed manual) :)

Sticks are fun to drive, but there's something absolutely stone-age about grinding an unlubricated piece of friction material into a metal flywheel to make the car move and then change gears.... especially when replacing that friction material means you have to drop the transmission and (usually) have to re-machine the flywheel.

It's no more stone age than stepping on the brake pedal. It's not like there's any significant slippage or wear in normal operation of the clutch, anyway.

nate

Stone age? I prefer to think "race car driver" seeing as how most race cars (except drag racers) use sticks.

Hey, when the dinosaurs were around, they ruled. :)

But modern clutches are so good now! I used to figure 50K miles on a clutch was good. It has been a long time since I replaced a clutch in a car, and I usually keep them for at least 120-140K miles. Many other things are falling apart on the car before then. Also used to replace throwout bearings- haven't done that in decades! And even when I did have to replace clutch linings, I NEVER had to have the flywheel machined.

Heck, my race car doesn't have ANY transmission- a non-shiftable quick change box (no clutch either). Car must be put in gear before pushoff. One can move it OUT of gear with engine running, but not into gear. This is standard with short track oval racing (midgets, sprints, etc).