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Old 03-02-2010, 05:36 AM   #11
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and I never said i wanted a "miracle" 90MPG Burb, all Im askin for is just a few small tips. other than the obvious: reduce weight, go easy on the throttle, coast to a stop, draft, windows closed, A/C and Defrost off, proper tire PSI. I was hoping yall could enlighten me on a few other lesser known tricks
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Old 03-02-2010, 06:05 AM   #12
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Weight reduction probably won't help. You'll need to remove 1000 pounds or more from that vehicle before you can begin to measure a FE increase. You can try, though; it can't hurt.

For lesser known tricks, the biggie is Pulse & Glide aka P&G. That's done by accelerating, putting it in neutral until you're going too slow, then accelerating again. It allows you to reduce the quantity of revolutions of the engine over the course of your trip, so less energy is wasted on engine friction and reciprocating loss. It also allows you to operate your engine in a more efficient range where it's producing more work (search for BSFC to understand that a little better).

P&G techniques vary. I've found that if I pulse uphill and glide down, it is most efficient AND reduces any issue of holding up traffic because my speed is more steady. Other people have found that using gravity assist for their pulse and then doing the minimum required to climb the hill works better for them.

Your truck has the 4L60E transmission which is known for premature failure in heavy applications like trucks. Mine has 192,000 miles on it and is still great, knock on wood. I've been using P&G for almost 20,000 miles without incident. I do rev-match when I go from N->D, which may help. That means I step on the gas so that the engine will be at the correct RPM already when the gear engages, rather than making the transmission force the engine up to the correct RPM.

Understand DFCO (Deceleration Fuel Cut Off) and your truck's DFCO behavior. That's when you're off the gas pedal but still in gear, you're engine-braking, and your PCM completely cuts off fuel injection until either you get down to 1000RPM or you step on the gas pedal. Each vehicle has a complicated set of rules for when it will and won't DFCO; my truck has to be engine brkaing for 8 seconds before it will DFCO. It's pretty worthless in mine. Jay's is more cooperative and he tried very hard to use DFCO as much as possible by downshifting, but that may have contributed to his transmission's early failure. OTOH, it's no more work for the transmisison than if it downshifts because you stepped on the gas, so it should be ok but I wouldn't recommend harsh downshifting either way.

DWL (Driving With Load) is another strategy. I haven't seen any theory supporting it but some people have had results. DWL is when you choose a position for your gas pedal and you hold it there, letting your speed change with terrain.

One modification that might help is an extended air dam. If you can reduce how much air gets under the truck, it may be more aerodynamic.

As a side note, you said you do heavy towing; when you do, you should increase your tire pressure for safety regardless of whether or not you want to save gas.
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Old 03-02-2010, 06:32 AM   #13
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Understand DFCO (Deceleration Fuel Cut Off) and your truck's DFCO behavior. That's when you're off the gas pedal but still in gear, you're engine-braking, and your PCM completely cuts off fuel injection until either you get down to 1000RPM or you step on the gas pedal. Each vehicle has a complicated set of rules for when it will and won't DFCO; my truck has to be engine brkaing for 8 seconds before it will DFCO. It's pretty worthless in mine. Jay's is more cooperative and he tried very hard to use DFCO as much as possible by downshifting, but that may have contributed to his transmission's early failure. OTOH, it's no more work for the transmisison than if it downshifts because you stepped on the gas, so it should be ok but I wouldn't recommend harsh downshifting either way.
Yes, there was a period where I tried to induce DFCO as much as possible (by downshifting). After a few months my torque converter failed. The truck was 9 years old with about 150,000 miles on it at the time. I am unsure if all that heavy DFCO lead to my torque converter failure, or was it just time to go anyway. Looking on the bright side, because I was extremely aware of the vehicle's "normal" behavior, and I was very strict on keeping up with my maintenance, I was able to detect this problem before it ended up causing the entire transmission to fail. I do not go to that extreme anymore, but I will still DFCO when going down steep hills, or exit ramps off the highway.

My truck is more cooperative than HC's when it comes to DFCO. My truck will enter DFCO after 3 seconds of RPM>1,500 & Throttle Position = 0. It will stay in DFCO until you either press the accelerator, or RPM<1,000.
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Old 03-02-2010, 06:48 AM   #14
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hell yeah id love to get a little 500 5 speed dodge shadow or something, but I can barely pay insurance for the one vehicle. if i buy another, ill have two insurance policies, two yearly inspections/emissions, two vehicles to maintain, and ill have to find space in the driveway for the second one. It would be great, but its not just a 500 dollar car, pay the 500 and done. yeah I live at home. what wrong with that. I commute to college. its only 20 miles away. so either pay 6 grand a semester for a dorm, 400 a month for an apartment, or live here with free room and board and free food. cant beat that. after college Ill have some money saved for my own place. but until then, im trying to save every penny I can. And I never said I frequently tow. but when I do, its heavy loads. plus the winters here are ridiculous and the township doesnt know what a snowplow is. so unless you got 4WD or AWD, youre screwed til someone with a private plow decides to run down the road.
The reason why I asked if you were living at home is because then it'll allow me to ask the next question... are you on the same policy as your parents? If you've got auto insurance and you're completely freestanding, expect to pay a lot more especially if you're young than if you just went under the umbrella of your parent's insurance policy. I don't know if you're already doing this but if you're not, you can save a bundle on insurance. Very heavy vehicles have high liability insurance as well because they're a bigger threat to others on the road. If the suburban is not yours, you could maybe assign the vehicle to your parents and then just get yourself your own car while still being able to drive the suburban from time to time. How much are you paying per month, per quarter or per 6 months?
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Old 03-02-2010, 06:10 PM   #15
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thank you cow for all the tips. ill try it. the truck has a new transmission as of 10k miles ago. truck is under my moms name and on her policy. I changed my plan a bit, so ill have to wait for my next statement to see what exactly it is now. space in the driveway is a huge issue in me getting a spare smaller car. after the weather gets better, they offered to let me drive the Camry. Unfortunately, I dont know how much longer that thing will last. im definitely getting a second vehicle when I get my own place. might try to air dam.
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Old 03-03-2010, 06:04 AM   #16
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hey, would a slight wind deflector over the rear hatch help any? maybe divert the wind drag a little?
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Old 03-03-2010, 07:29 AM   #17
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Here's a tricky one, which works best on roads you travel frequently.

Try to get a feel for the timing cycle of each light. Then if you see one turn yellow/red, hit the brakes as soon as quickly as you can to slow as much as possible, so that you:
1) Get to the light exactly when it turns green, and
2) maintain as many MPH as possible.

If you wait too long to brake, you'll have to slow down more, or even stop - but if you hit the brakes early you can hopefully maintain 20-25 MPH when the light turns green.

Obviously this is harder to do when you are not familiar with a traffic light.

-Bob C.
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Old 03-03-2010, 07:32 AM   #18
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hey, would a slight wind deflector over the rear hatch help any? maybe divert the wind drag a little?
No, but what may work is if you were to fashion a kammback for the rear. That is something on my list of things I would like to eventually do, but I've never gotten around to it.
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Old 03-03-2010, 08:04 AM   #19
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how would I fashion a kammback? it would render the liftglass useless. when its opened, the glass is above the roof line. got any ideas?
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Old 03-03-2010, 08:25 AM   #20
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My thoughts were to fashion one that attached to the frame of the rear glass. Last winter my truck was parked nose into the wind during a blizzard. The resulting accumulation of snow on the back glass was a perfect kammback. I wanted to take photos, but my camera was in the back of the truck. I wished I could have taken many pictures & measurements so I could have replicated it.
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