Mathias

Maybe should do the trick.. No, the 235´s are skinny enough.

pandin

Not only does the mpg calculation change with, the increase of tire size or rear gear. The load does per mph.

This is opposite to a drag racer, who lower the rear gear to increase torque a set speed. As echoed across 3rd Gen "you can run up to 3.73:1 and still drive at freeway speeds"

A drivetrain does not make more power, read this as the differrance between FWHP and RWHP. It only uses HP. Manual is less of a loss than an auto. What is that, up to 20%. The guys with the 6 speeds know that. They lose less. It is "free HP" Remember way back, when sticks got better mpg then autos.

Nothing is free. There is a trade trade off between torque and RPM. As the drivetrain gear ratio changes, say you shift into 1st gear, engine torque is multiplied speed is reduced. In OD speed is multiplied and torque reduced.

The challenge, any time you are in OD you lose more. It is more efficient in a gear set to reduce speed to gain torque than increase speed and reduce torque. This is used by the big rigs, Hi torque motors and under (more torque)over (more speed) trannys.

As was pointed out, as the tire size increases, the drivetrain ratios have to go down to stay at the original spec. If not than load increases.

If this change is not done, then load will increase. No big deal. but what about good ol PE. At some point, with a stock tune, your engine will pass over into PE land (80% load ???) and the mpg go south. Way south.

At this point you have options regear, remotor , or retune.

Regear, as mentioned above, lower drivetrain ratio (use 3rd instead of 4th)(change rear gear $$$) Go to drivetrain tech board for more how to info.

Remotor, install bigger motor, has more torque. get under the 80% BSFC.
Try the general motor tech board.

Retune, match the tune to the motor vehicle combination. but there are no TPI trucks. Use TBI? If you got your TPI in a truck then the chip has to be tuned to that combination. That is why this is at Tech board DIY PROM.

Fast355

iTrader: (2)

Definately wrong. I have a Dodge Quad cab truck with a 4.7 and 6spd auto in it. 5th and 6th are both OD. I have tried running the truck in both gears on the highway and just about always get better fuel mileage in top gear. That gives 2,000 rpm @ 75 mph. I have seen 20-22 mpg on a road trip running a constant 70 mph.

pandin

That is great. but what about the guy that is getting 11 mpg.

What is the differance? How does he find the 20 mpg sweet spot using a TPI?

jcs64

yeah,what about me? LOL
I just filled up yesterday a showed 10.9 mpg
W/ the tire deal, Right now Im running a skinny 29.5" tire .

pandin

Do search on mileage and performance. Grumpy (rip) had some very good words of wisdom.

Also there is a thread, my cut and pasted copy runs 8 pages. Grumpy is one of the posters. I didn't copy who the authors were. It was only for my reference.

The first line is " So you want to save some buck well here are things I've implemented on some of my tunes over the years that have increased gas mileage."

There is a ton of mpg info in this thread. specifics on 6E and other Bins.

It is too long to post here and I can't give credit to the original authors.

If anyone remembers or is an author, and has the link info. It would really help this discussion.

BTW The discussion I have presented so far is my own silly thoughts not borrowed from any other source but what I have seen in the past.

I will be reading the eight pages to see the flaws in my thinking.

There is more to be learned by being wrong, than right all the time.

This is a Quote from one of the threads:

pandin

drowning in tbi

Just to throw in my .02. An engine-any engine will be most efficient at its peak torque-meaning the most output of energy to unit of fuel. At this point we are making maximum torque-not the best way to cruise down the highway.What we are looking for is the least amount of fuel to make the power it takes to maintain a given speed, on the highway=not much power. So from this we can work on tuning for best fuel mileage. The egr won't make an engine more efficient-it will cut down on pumping losses by adding an inert gas to help fill the cylinders. When your tune is the best it can be for fuel savings-then you can add egr and start the tuning over again.

jcs64

still good info coming in!
Pandin, thanks for putting up that AFR limit chart. Currently my highwaymode is set at 15.5. I had been wondering if I dare push it any more, now I see that 16 is still OK.
Well make the change and see what happens.

I just filled up yesterday, another 10.92 mpg! arghhh!

pandin

The weight of the vehicle and cruising speed has to match the engines efficiency range. A high overlap cam run at lower engine speeds is not a match (the cam was changed to RV type). Running the engine, at cruise speed, in the PE mode is not a match (raised the PE cut in spot, slightly richened the main AFR below that point).

jcs64 more is not always better.
Do not just lean the engine, there are other issues to watch, like melted pistons, from running too lean, too long, too much load.

If your results do not match your expectations, try doing the opposite, you may be surprised.

To stay out of PE mode a little richer AFR at cruise may be needed not less.

At cruise speed a lean AFR + PE = low gas mileage.

Higher AFR without PE = better mileage.

This principle came from a Peterson's Publishing book, bought back in the 80's,

Rochester Carburetors & Emission Controls : Quadrajet, Two Barrels, Monojet, 4GC (Paperback)
by Doug Roe (Author)

I am not an engineer. These are just my observations. The two vehicles that I owned and Tuned got a lot better mileage. I don't have a clue why. I know what I changed and I know what the results were. Just trying to help out.

MarcusMandarino

Hello

I'm looking for $0D .adx file for ScannerPro...
Can anyone help me?

Thanks in advance

Marcus

83 Crossfire TA

iTrader: (2)

This couldn’t be more true and is often ignored by most people, they think “if I want better gas mileage I’ll just run it leaner, and if I want more power I’ll just run it richer…” Just like running an engine overly rich will kill power, running it overly lean will hurt gas mileage.

The thing is that unless the engine was originally optimized for lean burn and a well balanced happy combination operating in it’s optimum power band, as you go leaner than where it makes max power at that rpm, the amount of power it makes starts dropping off, and the farther you are out of your power band, the worse this is. So you might be in highway mode and the ecm is calling for 15 or 16:1 A/F ratio, the power could drop off so much that you have to give it significantly more throttle resulting in significantly more fueling (especially if that puts the engine in PE), resulting in really awful gas mileage.

You can cover up that loss some by adding ignition timing, but then you risk rattling and melting bits, and even that tendency can be dealt with some by adding some EGR, but again, that can hurt power… you’re in an even more delicate spot around the torque peak where your cylinder pressure is the highest….

Basically, what I’m getting at is that in a lot of cases unless things are optimized for that lean burn condition, you might find that you actually get better mpg around stoich or maybe even slightly richer

83 Crossfire TA

iTrader: (2)

Being another full size truck owner (’92 K1500 Blazer, the 4wd probably puts me in a similar place WRT to drag as your suburban…), I think that people in this thread are _way_ underestimating the affect tires have on the situation. Yes, tire size changes make a difference in effective gear ratio, but that’s not the only thing.

For example, when I bought my truck it had 265/75-16 goodyear aquatreads (Don’t look at me, I didn’t do it), and I replaced them with some 285/75-16 BFG AT KO’s (roughly going from a 31” tire to a 33” tire).

Now if there was nothing but a height difference, you’d expect the slightly better final gear ratio would help slightly (3.42 gears and a 700r4 transmission), at least at my relatively high highway cruising speed. There is a little less than an inch increase in height which will hurt aerodynamic drag slightly. I would be surprised if that minor increase in width makes a significant impact, so if everything else was the same you would expect to break even or be very close. IRL, on the shorter aquatreads I was getting 14.5-16mpg depending on what was going on to a very consistent high 12 with the goodyears (it’s actually very difficult to document any mpg change whether it’s all city, all highway, unloaded, fully loaded pulling a heavy trailer…).

I would argue that the big change is the result of 2 different things… first tire construction/tread design… somewhere in the different manufacturer’s AT truck tire line is a clear point of delineation where tires are optimized for traction and durability offroad and more practical considerations on road, including MPG. I would argue that the BFG AT’s fall more on the side with the MT’s and other offroad tires then something like a Yokohama geolander II or even more so, tires optimized for highway use like the firestone steeltex line.

Second, these things are just plain monstrous compared to the normal car tires that we’re used to. For example. Check the weight of the 285/75-16’s, they seem to average about 55lbs, and I would have no doubt that even the relatively small factory 16x7 rims on the truck are easily pushing 30lbs, putting each wheel/tire in the 80-90lb range, compare that to a third gen tire on 15x7 or 16x8 rims, most of which fall in the 32-45lb range, even the factory convex “high tech” 16” Pontiac rims which are enormously heavy for that kind of a rim still usually total under 55lbs. I have a couple of sets of 275/60-15’s which are about as close to truck tire sizes as you’re going to come on a car (fairly tall, 28” tires that are fairly narrow for the height, but close to the width of a lot of the truck tires), the set on some factory 15x7” rims is about 39# each, and the set mounted on some 15x9 draglites is much lighter than that (FWIW, I’ve run 37mpg on the street in a TA with similar sized tires, 255/60-15 on some factory 15x7’s).

Now remember, the amount of energy involved in something spinning is affected by both diameter (the term is squared, so exponential) and it’s weight has roughly 4x the affect of that same weight just being carried by the vehicle.

I would argue that something like Fast355’s examples, though impressive, in many ways is more comparable to trying to do it with a car than with a truck, his gearing, tire sizes and weights are much more car like than what we’re dealing with.

All that being said, I would suggest that what actual size and model of tire you’re running is probably more important than “I’m running 33” tires”

Tbi-MAX

true, they will measure slightly less that 33" more like 32.8.... im looking at the Mickey Thompson MTZ... specifics are 33x12.5x15 this is what the website says.
http://store.summitracing.com/partde...5&autoview=sku




so yea.... i can expect to loose mpg VS a AT tire.. since im going with MTs for the look i am after. The speedo had not been adjusted, im doing that when i switch my gears. so in reality i dont think the truck lost any mpg from the tire swap. i have a set of 4.56 gears waiting to be installed... i know that will be lil overkill for a 33" tire.

jcs64

dont forget that if your speedo is off, things wont be happening when there supposed to ,such as highway mode.


Im making some changes right now to richen my mixture in highway mode to 14. Im currently leaning it to 15.5 so Ill try going the other way.

Ill give it a 1/2 tank and see what happens. Then I may even try changing the base AFR setting from 14.73 to 14, which should should show a definite change whether its good or bad.

Does that line of thinking make sense?

83 Crossfire TA

iTrader: (2)

Highway mode calling for a richer then normal mixture… not sure what would happen, I wouldn’t be surprised if it did something unexpected.

Why not just turn highway mode off, that would be a more reasonable step to see if that helps MPG anyway. Another thing to experiment with would be setting the PE threshold MUCH higher to see if it might be that you’re forcing it into PE during your normal driving.

As far as tires… I’ve got a dilemma going on there. My truck actually sees a fair bit of actual off road use (it’s not uncommon for it to be buried up to it’s axles in mud once a month or so during legit, “I have to be here” type use), I would also prefer to keep something fairly wide on it because it’s not uncommon for me to use it to move heavy equipment across the lawn into the shop/basement door and I don’t want to leave ruts, and finally I need a decent load rating because I do some hefty towing with it a few times a year.

The 285/75-16 AT’s are a pretty good compromise there. Enough tread and size that I rarely have to even turn the 4x4 on, and being load range E tires, perfect for heavy loads. But it turns out they are a bit wide for the factory wheels (I actually have had the beads unseat from the wheels a few times just parked, never a problem on the road)… they really want a 9” wide rim which I can’t seem to find anywhere (at least not for a reasonable price… I really care much more how this truck functions than how it looks).

Now considering the rest of this, if I was going to buy rims anyway _I would prefer_ to go with 15” wheels, large enough to still clear the brakes but the smaller wheel will weigh less helping this whole gas mileage deal, and in a perfect world they’d be slightly wider and maybe an inch shorter (somewhere between the stock 265/75’s and the 285/75’s in height) just because I have just caught the lip of the front fender with the tread a couple of times, amazingly on the street, not off road. The thing is that I don’t believe that there is a common tire size in that range that has a decent load rating.

jcs64

IT WORKED!
yeah, to soon to get excited, I know. but, I topped of the tank today and it showed 11.56 MPG. (pretty sad getting excited over a 1/2 mpg improvement)
This was even achieved while I had a high idle problem and and a code 22. Not sure what that was all about, but I reburned the chip when I got home (used the previous one to get me home) and now its fine.
Ill leave it the same for a while to see if it repeats before I go changing it a little more.
As for the other stuff you mentioned,
-PE is already set high si that its out of the picture
-Highway mode was already disabled when I started, im just starting to experiment w/ it now.

pandin

Glad to see your getting some results.

You could also experiment with Highway mode, a little richer and more spark adv. Under a lower load condition may gain a little. Becareful richer + spark adv hides detonation.

kevm14

Funny you should mention that. I bought a 91 Ranger recently (hey, the price was right and the truck is clean and only 71k). It's the 2.3L OHC 2wd plus 4-speed auto. The EPA ratings on this truck were only 21/23. But as if that weren't bad enough, I've not broken 19mpg, even on the highway. Part of the reason may be the winter gas, but I think a lot of it is the sucky Ford calibration. For whatever reason, this truck won't stay in closed loop on FLAT road (according to my XP240) much beyond about 65mph. I have no idea why they did this. It's not even that the truck needs a ton of throttle at 65 on flat (short gearing). In fact, idle TPS voltage is 0.9 and it seems like it goes to open loop (PE?) by 1.9 volts or so. That's not a ton of throttle. Sorry to corrupt the thread with F*rd crap but it has been bugging me lately. It's even more frustrating when you realize the truck has multiport/MAF/CnP ignition!

jcs64

No good, it was just a fluke!
But maybe not totaly.
Last fill up showed 10.47mpg which is even bellow average. I also had the code 22 come back, and now its even coming on w/ my "safe chip".
Looks like its off to the parts store for a new TPS

pandin

PE is power enrichment. If you are carb inclined its is the power valve.

At some point of load (vac) the engine tune is richened by up to about 25%.

20 mpg - 25% = 15 mpg

ggenovez

Code 22 is a TPS error. (low signal voltage).

I guess many of us with the large gas sucking beasts are getting into the EFI tuning now that gas is going to shoot over 4$/Gallon.

Being a newbie myself and overwelmed with information is there a link that shows what setting is linked with what setting?

Like I see PE (Power Enrichment)

On Tunerpro I have a choice of
PE mode spark advance
PE mode VS TMP
...VS Rpm

VE (volumentric efficiency) was mentioned, I don't see anything like that in the e6.xdf.

AHHHHH!!!!!

Is there another XDF I hsould be looking at? Is there a fuel efficiency XDF that only deals with the fields needed to modify?

I'm running a stock 90 burb R1500 700-r4. On a all highway trip I got a whold 13 mpg.

Excellent post. Excellent thread. Thanks to all who post & make this forum possible.

pandin

Weclome to TGO.

This is Automotive engineering 101,102, ect...... You have just taken your first steps on a long trek, enjoy the path you take.

jcs64

little update here,
A couple weeks ago I switched back to my summer tires (33"x 12.5" x15, I was running 31x 10.5r 15's). I wasnt sure what to expect at my next fillup. When I first got the jeep (w/ a 350 and "91 TPI setup) I was getting low 9's mpg. I just did my third fill up w/ an average of 12 mpg (highest was 12.15 mpg yesterday).
I did pick up almost 1 mpg more by going w/ bigger tires, I guess that really screws w/ the theory that big tires hurt milage.

Now I just need to fit the 38's under there! LOL

antman89iroc

Ok, hopefully I'm not getting too off topic here but...

I understand that an engine is most efficient at peak torque (not talking about fuel mileage here) and it is obtaining the most amount of power (hp) from "x" amount of fuel. Now the problem is that the amount of power required to maintain speed "y" is less than generated at peak torque. Therefore, the best fuel mileage (mpg) would be seen at engine speeds less than peak torque because the reqired power is less. IOW the engine isn't more efficient, it's simply making "enough" power to maintain speed "y" while consuming "z" amount of fuel.

Or have I misunderstood this? redngold what do you think?

Opinion: Performance and economy can (and in my opinion should) coexist. Yes, there always seems to be a trade off. However, I always tune with a goal tward one with the other close behind. I get the most satisfaction from combinations which deliver outstanding performance AND economy.

itawolf

my hardbody nissan gets 30mpg on the highway running 33" and a 3.0 v6 auto but with 225 tires the milage fell to 21mpg

all i can say is big tires cover more distance maybe thats why??

RBob

iTrader: (1)

Or, because of the tire diameter change the odometer is now off and the results are meaningless.

RBob.

DM91RS

Going back to earlier comments about delaying PE with the PE-TPS% settings, what would a safe range of delay be? Mine are now 40% @1600 and 46% @ 2400. With a .63 od gear even with a 3.73 rear and as many hills as there are on the interstate I most likely envoke PE quite often. This can't help mpg.

Thanks.......DM

malcom2073

EDIT: I'll put this in its own post

Ronny

iTrader: (1)

I think the stock 7747 $42 mask had invoke as high as 70% TPS if I read that right. commercial trucks. I would think staying out of PE is a good idea for fuel consumption. AE will get you moving then you run off the VE tables.

DM91RS

Sounds good to me. I'm gonna up my percentages some and see how it will do. As long as it does not hesitate when applying throttle to keep moving at the same mph it would seem is all you need.

pandin

You will need to up the fuel alittle in the ranges that are not covered by the increase in the PE vs TPS %.

You need to know what the maf/map area is, that you uncover by upping toward 70% TPS. Then add 2-3 % more fuel, PE adds up to 25% more fuel. This difference in % added fuel is were the MPG increase comes from.

If this was a carb metering rod you are effectively making the taper from cruise to power, long and gradual, instead of short and steep,

Your AFR should transition from 14.7 towards 13.2 (lean torque) in this uncovered range. PE would then take you to best power then on to rich torque, under even more load (steep hill, passing).

You need enough more fuel, to pull all the little hills, and save the PE for the big ones and passing.

DM91RS

Thanks, I'll be trying this soon.

DM

itawolf

dumb me---guess I wasnt thinking--but it did a good job on the brain

pandin

Something to watch when tuning for MPG.

If the O2 sensor goes cold (around 600 F) then the ECM thinks the mixture is lean and will richen to the point of stall. Watch the cross counts and the MV output if they are low then a switch to a heated NB O2 sensor is in order.

This is also the cause of it, smells/runs rich but reads lean (160 BLM) at idle.

Grim Reaper

The problem with max BFSC/TQ only works IF the car operates in a vacuum. Once you add air resistance, that equation is affected.

I did MANY tests on my 91 GTA to obtain it's best fuel economy a number of years ago (when my engine was still basically stock). I got my best fuel economy at a steady speed just shy of 60 mph which was about 1,800 rpm. That was NOT it's peak TQ of BFSC (which was probably closer to 3,200 rpm).

If there was NO air resistance, then it may have been but with air resistance, it happens at a much lower rpm because of the high air resistance that occurs at the speed when the engine hits 3,200 rpm.

DM91RS

What drive train did you have in the car when stock?

Thanks......DM

ggenovez

& what did you use to determine the best fuel economy? was it readings from your TPS or get on the highway hit cruise and drive for 30 miles?