Fuel mileage conundrum

[fzj80kidpen]

Doug,
Did you actually record all mileage and gallons consumed by both. Just want to make sure we are not racking our brains to due to sibling rivalry. If I was your brother I would have to chasing your tail by misleading you about my MPG if I thought I could get away with it Then let you in about a week later
But seriously whats the PM like on your O2 sensors and whats that other one that has to do with EGR is it VSV or VCV. I forget what it is but it is in that same location under the intake manifold. Did you already check tire pressures?
Not ask but check, you are usually pretty thorough just trying to eliminate the brother practical joke factor.

 

[Hayes]

ECT won't have any effect if cruise control is engaged. Just accept that the '93 is a better rig.

The 93 has a better transmission...

Hayes

 

[Nay]

I believe it is the PWR button. Are his tyres the same diameter as yours? You said 265 vs 275 but that is only part of the equation to decipher the diameter.

-B-

PWR button doesn't change the OD gear ratio...no affect on highway driving unless you had to downshift a lot, in which case it probably helped you, because you weren't sitting with the pedal to the floor at 1,800 RPM trying to get the damn thing to actually shift down only to have it drop right back into OD lug-mode anyway.

The real question that is arising from this and other posts is at what point you will have spent more on the extra OCD stuff than his truck is worth

 

[Tuner]

Two different year model trucks...I bet he'd trade for yours even with worse mileage

At the risk of revealing the depth of my ignorance from the old v-8 days, I think advancing the timing means the spark plug fires a good bit before the piston reachs top dead center on the compression stroke....resulting in slightly more power but also increasing the pressure on the combustion chamber, pistons, connecting rods, etc. The most forgiving place in that equation is the HG....am I way off base?

BTW, I've been hand calculating mpg for a while and it is pretty steady at 12-13 in town with a semi heavy foot and 16-17 on the raod at 70-75.

 

[OZCAL]

Doug, you're a bike racer right? Was your brother sitting on your wheel?

 

[Grouseman]

IdahoDoug,

Great question. I can remember just a few short months back when I was asking questions about mpg with differant tires, and modifications. Everybody was saying hey you shouldn't have purchased a Cruiser if your worried about mpg. Now look where we are.

Grouseman

P.S.

Doug this wasn't directed at you at all. Just a general statement

 

[Gumby]

Easy.

His rings have finally broken in. Yours is still too new.





There are a ton of little differences I could see as the difference. Different emissions. Different engine management. Different transmissions (although both should have had locked TQs on a highway trip) Different break in. You tow a boat in the mountains country. I could see your compression being lower from that dispite the mileage difference. Anything different aerodynamically? Roof racks, rear window deflector, bug deflector, window drip sheilds? Running A/c or windows open? Dragging brakes are certainly an issue for the 80 series. Both p-brakes and sticky clalipers. Are you running 100 series pads with him on the 80 series?

 

[cary]

I'll throw one out that hasn't been said, gear ratios. Does the 93 have the same 4th gear ratio as the 97 tranny?

 

[cruiserman]

0.765 (A442F) vs 0.753 (A343F)

 

[OZCAL]

AHA! Doug, did either of you engage the cruise control?

 

[PhILIE]

I'm the process of trying to determine how much a bad ac clutch will cost mpg wise. I got almost 2mpg better mileage after slicing off the ac belt after meltdown. This is all theoretical at this point and I know that other factors are involved, but once I get it fixed I want to see if I go back to original or maintain the better MPG.

 

[Cruisin'Carolina]

Can I hijack for one response?

I have a 94 with 94K.....newish Revos of the 33" flavor.

I just traveled what reads (speedo uncorrected) 215 miles, took 17.587 gallons to do it. Combo city, mostly highway miles running at a good clip....

How do I adjust? Are the revos (285s) truely 33"???

 

[alkaline747trio]

285/75r16 would equal a 32.8" tire. 31/2 = 15.5 15.5^2 x pi = 745.767635. So w/ a stock 31" tire, you travel 745.767635in or 62.89730292ft or .011912368mi per revolution. 32.8/2 = 16.4 16.4^2 x pi = 844.9627601in or .0133359021mi per rev. So... 215mi/.011912mpr = 18049.02619 x .013335mpr = 240.6837 actual miles traveled. 240.6837/17.587 = 13.6853mpg.

 

[C6H12O6]

I would think a properly inflated, taller, skinnier 265 tire would have a smaller contact area on the road than a properly inflated, wider 285 tire does. That should help, not hurt the mileage, assuming the 265 isn't significantly heavier.

Have you figured out the math to see what effect the different gear ratios would have on total engine revolutions? I would think, at highway speeds, there would be a pretty comparable volume of gas per cylinder firing. More cylinders firing off would use more gas. Maybe not 13% worth, but you might be looking at more than one variable here. So far, I see ignition timing, tire size, giant baby weight, ???.

I'm also not convinced the PWR button really has that much effect, especially at highway speeds. Once you are up to speed getting your best mileage, it's probably a wash. Even getting up to speed, it feels to me that I push the pedal much harder with the PWR button off to get up to speed. I'm planning on running a comparison test of a couple tanks each with the PWR button on and off to see what effect it really has under similar driving. I would think a deep pedal at low RPMs wastes as much or more fuel than accelerating smoothly to a little higher RPM with the PWR button. Same effect with the kickdown? We'll see.

In any case, driving with the same road rage lead foot every tank is tough. That makes it hard to set up a very valid experiment unless you can devote so many tankfuls worth of driving to the test so as to get rid of any weird blips in the data. Doug's test is as good as you can get with two vehicles. Now we just need to figure out what all the variables really were and try to see which one/ones are to blame.

 

[cruiserdan]

0.765 (A442F) vs 0.753 (A343F)

That and tires.

To get that "apple" Doug both vehicles need the same tires. I thinkk the tires are a main difference.

 

[Bearcat80]

Yup, Tires.

When I went from the stock Badyear Wranglers on the wife's Heep Liberty to heavy Toyo A/T's (no size change) it sucked the MPG down an average of 1.5 MPG. Add that to the Winterized Gassholine we have here in the People's Republic of Portland, and the little tank sucks it down at 13.8 mpg for the Mrs. daily commute. So don't feel bad, Mr. Idaho, at least it's a Toyota you are suffering for, and you have some room in the back.

 

[RAYJON]

As info ... having had this same issue and didn't understand why... Called a freind of mine who has done alot of dyno testing and map programing for aftermarket computers and asked why would my air door outdated 93 get better mileage than our 97 ever has... His answer was simple different computer tunes.. one is geared to performance and mileage and one to emisions. OBD 2 did some great things for the emisions of the vehicle but it forced the MFG to change the computer maps to meet the emisions...thus hurting milage... interesting trade off....

Personally I think my 93 has better throtle response and pulls harder in the middle than my wifes 97 ever has.. just the seat but dyno no facts.....

Another example is my 92 dodge diesel get better mileage consistantly than my bro's 98... 5-6mpg different... same gears, tires, and trans ratio, different tune on the pump and injection timing... is the main difference....

 

[medtro]

285/75r16 would equal a 32.8" tire. 31/2 = 15.5 15.5^2 x pi = 745.767635. So w/ a stock 31" tire, you travel 745.767635in or 62.89730292ft or .011912368mi per revolution. 32.8/2 = 16.4 16.4^2 x pi = 844.9627601in or .0133359021mi per rev. So... 215mi/.011912mpr = 18049.02619 x .013335mpr = 240.6837 actual miles traveled. 240.6837/17.587 = 13.6853mpg.

Something is not right here, Radius^2 x pi gets you the area of the circle, not circumference.

 

[scottm]

Bro, you advanced the timing on my '97 same as yours. Last night I finished a tank on my O'Hare & back run, 15.3 mpg. That's on stock tires, fighting rush-hour traffic and cruising 75 - 80 mph (mostly 78 mph). Thule standard height rack with two fork-mount rails. Check engine light on, probably running open loop for the O2 sensors. I've seen 16 mpg at lower speeds, heavily loaded with the cargo box on the roof. The 40th always seemed to get worse mileage with it's knobby 265s.

And I rarely unleash the force of the PWR button.

 

[T Y L E R]

Something is not right here, Radius^2 x pi gets you the area of the circle, not circumference.

Multiply his data by 2/r to get circumference based shtuff ..



TY