Pulse & Glide with Automatic Transmission?

[abell75]

What are people's experiences with ATs and P&G? I have done a bit of P&G (not enough to draw a conclusion on it's effect yet), but as I read other threads I realize that in my effort to optimize my time at optimum throttle while accelerating, I'm unlocking the TC when I hit the gas and the AT downshifts as a result.

My commute is a combination of 65 mph and 35 mph speed limits, with a few stoplights in the 35 mph section.

Am I better off to just keep the TC locked?

[JasonG]

If its down shifting it sounds like you need to let up on the gas pedal.
Can you force the TQ to stay locked ?
See Torque Converter Lockup - EcoModder and related question http://ecomodder.com/forum/showthrea...ion-16149.html

[bluejoey]

Yup, if you're downshifting when you accelerate, then you're probably accelerating too hard. Frankly, I've also found P&G doesn't yield nearly as good results on my AT Tercel as does DWL in concert with gliding to stops. However, things might be different in your Grand Prix. I'd recommend an Ultragauge to help you test out the difference.

[abell75]

Thanks for the advice and links guys. I have an Ultra-Gauge that has been very helpful so far. I love it, though I'm only on my 2nd tank of fuel with it.

I was trying to get 40-50% load during accel in order to get better efficiency based on BSFC islands, but I do think that the downshifting was a net loss due to the TC unlocking.

Aggressive P&G on the freeway is also a lot more work and I'm fairly confident it's annoying to those around me and less safe (constant speed changes make me unpredictable). From now on I think I'll just set the cruise - I drive on rolling hills so I'll have a little bit of P&G anyway, without the shifting (my 3.8L has plenty of torque lol).

Probably should do some A-B-A testing to confirm the results.....

[bluejoey]

On the freeway, when driving cars with cruise control, I basically turn it on at a speed between 60 and 65 and leave it there; it's a lot easier than P&G. When driving my car, which doesn't have cruise control, I DWL between 40% and 60% while keeping my speed between 55 and 65. This clearly requires instrumentation, and it's much more work than CC, but it doesn't restrict traffic much and it's much more efficient in my car than P&G at those speeds.

[SentraSE-R]

I've found P&G makes a couple of mpg difference improvement over cruise control with an AT. Like you, I think it's a little unsafe and a lot of work. But it does seem to help. I've done some ABA testing that seems to verify the improvement.

You definitely don't want to unlock the TC. I've found on my wife's Elantra that keeping engine load below 70% keeps the TC locked, so I accelerate with ~60-65% load in our Elantra, and try to keep under 70% load on uphill grades.

[Sularus]

I too have a grand prix abell. I just use the cruise at 50-55mph and coast as long as possible coming to stops. If you don't have the supercharged GP, I wouldn't go above 60-65. The gearing in our cars isn't that great compared to other W body cars. I tried P&G, but it is easier to just cruise. Not to mention most of my commute is 2 lane so it tends to upset people around me.

[abell75]

No supercharger on mine. I've started to focus on keeping the TC locked instead of accelerating in the 40-50% load range (above about 35% seems to trigger a downshift) and the results have been significant in a positive way - from 25 to about 28.5 mpg! It's a small sample size though, only two days or so....

[Sularus]

It does make a difference. I am trying to get a ultra guage, but too much stuff going on, not enough money. Also, try to keep your speeds below 60-65. The gearing in our cars, and the crappy rear end aero, doesn't help us much above 60.

[SentraSE-R]

I've averaged 42 mpg with a rental AT Yaris w/2 people for 3 tanks in New England, and 43.4 mpg with a rental AT Kia Rio w/3 people for 3600 miles in the Rockies, doing a gentle P&G routine. I got >49 mpg with the last 2 tanks in the Kia, & would have averaged >45 mpg overall with it, if allowed to throw out 2 outlier tanks when I was fighting >45 mph crosswinds in SD.

I couldn't break the 40 mpg barrier with my wife's AT Elantra until I started P&G with it. I hit a wall at 38-39 mpg. Since I started P&G with it, I can routinely get 40-42 mpg on long highway trips.