Author Topic: Fuel mileage (Read 4489 times)

crx-si · « **on:** Mar 20, 2006, 08:44:25 PM »

What is everyone gettin i have an 85 carbed 4x4 with stock tires, and no modification and new carb. I'm gettin about 12 or 13 MPG. I forgot to mention it has an 87 22re block in it would this cause a difference in fuel mileage.

lilbuddy · « **Reply #1 on:** Mar 20, 2006, 09:10:06 PM »

Just to let you know, there are about 3 recent threads about what sort of MPG people are getting...

81 carbed with stage 2 cam, exhaust, header, 37s dual cases and 529s, about 19 freeway and 15 town. About 11 wheeling.

BigMike · « **Reply #2 on:** Mar 20, 2006, 10:27:23 PM »

Hey! Well, I have not been around for a while, but I just thought I would share some new news I have experienced about Fuel Consumption, which mainly deals with EFI systems.

When I first started driving, I had always wondered what was happening when you let off the gas and coast. Is gas still going into the cylinders? Even with the throttle closed? Is it better to coast, for instance, down hill in gear or in neutral (engine idling)? Does coasting in gear require less fuel then it does for the engine to idle?

Well, thanks to the new version of my OBD-II scanner software (http://www.obddiagnostics.com/), there is now a "Performance" Feature that includes the real time fuel consumption vs. miles traveled (or MPG) display.

My original consent was that it is better (uses less fuel) to coast in gear with the throttle closed than to be coasting in neutral with the engine at an idle. I thought that at an idle it is using fuel to keep the pistons moving whereas while coasting in gear, no fuel (or a very small amount) is needed because the momentum of the vehicle is keeping the pistons going (conservation of energy). I have heard many times that if you have to idle your truck for more then 1 minuet, then it would save you gas if you were to turn the engine off, and then restart it when you are ready to go. Apparently the amount of fuel needed to start an engine is approximately the same amount of fuel that is required to maintain an idle for 60 seconds, or at least thats what the "myth" is anyways... (has anyone else heard this?)

However, with the Scanner hooked up, I find that it is quite the opposite.

When I am on the Freeway doing 80 MPH in 5th gear, according to the scanner, my truck averages about 18.5 MPG in order to maintain 80 MPH. There is of course a drastic change if I were to accelerate to say 90 MPH (pegs my speedo at 85), then the scanner reports about 11 MPG for about a 80% load.
The story is the same for coasting. Coasting in 5th gear from 80 MPH to 70 MPH, my truck will average close to 95 MPG.

But, if, at 80 MPH, I throw it into Neutral and coast, off the gas of course with the engine at an idle, the Fuel Mileage will rise upwards to 150 MPG.

Therefore we come to the conclusion that RPM is the Ultimate Fuel Mileage KILLER!!

I have found out that if I accelerate my truck while shifting before 3000 rpm, I can keep the average MPG during acceleration above 21.

On a related question, one that again has always been in the back of my mind since I started driving, is comparing 4th gear at 3,000 rpm with a light load vs. 5th gear at ~2500 rpm with a heavier load, both at the same vehicle speed. I have always thought that, for the same speed, less fuel is required if you are in 4th gear (at a moderately low rpm) with a very light engine load (10-20%) than if you were to be in 5th gear (at a lower rpm) with a higher engine load (25%+). My reasoning is that it is easier to maintain the vehicle at 50 MPH in 4th gear then it is to maintain 50 MPH in 5th gear, simply because at that particular speed, 5th gear is under a slight load or bog whereas in 4th gear the engine is much more freely spinning. Their is less of a load on the engine, so therefore less fuel is required in 4th gear.
Of course we have to consider the RPM of each case. The RPM in 4th gear is maybe 500 rpm more at 50 MPH compared to the rpm in 5th.

But again, my original thoughts were wrong. As in the first question, the issue with RPM arises.
Cruising in 4th gear at 50 MPH and (I don't remember the exact rpm) let's say 3000 rpm, my truck makes 21 MPG according to the scanner. But at this same speed in 5th gear, the rpm is, well lets say 2500 rpm, and my truck is now making 24 MPG.

And yes, you are reading that correctly, for my truck, engine, tire size, and climate that I live in, makes better mileage cruising in town then it does on the freeway. And this is largely due to the fact that I have a mismatch with my Tire size and axle ratio. I am running 35" tires with 5.29s, but I should have 4.88s for this tire size. Unfortunately I can not stand driving any less then 70 MPH on the freeway, so I suffer from that in the MPG department because my engine speed is always above 3,200 rpm in 5th gear. I am sure that once I get 37" tires that my gas mileage on the freeway will go up at least 2 miles per gallon.

For the data, my truck averages 23 MPG in the city and 17 MPG on the freeway, under my driving habits. Of course when I pump gas and computer the mileage vs. fuel used, the numbers are not far from the scanner data. My combined Freeway and City driving is always between 17 and 17.5 MPG. I typically get 250 Miles out of 14.5 gallons (16 gallon tank).

This has prompted me to take some screen shots of the scan tool and show you guys some real positive proof.

The only thing wrong with all of this is that, again, the poor tire-axle choice that I have right now leaves my truck with a speedometer that is about 4 MPH too fast. 54 MPH on the speedo is really 50 MPH compared to the ground. This is I believe is good for a 0.7% error in all of my calculations, and in that of the scanner also, since the OBD-II system gets its MPG data right from the Speedometer (internal speedsensor). So if I am averaging 17.5 MPG combined, then I am really only making 17.38 MPG, and therefore, for all practical reasons, I just ignore it.

Again, I will take some screen captures of my scanner the next time I am out with it!

Also, I drove around with my tailgate down and with it up, and I didn't notice any difference in real time. Perhaps there is a difference over the 250 miles that I travel between fillups, but I have yet to determine this.

Also, coasting to red lights with the tranny in neutral and the engine idling instead of leaving it in gear and using the compression of the engine to aid in braking, can save considerable amounts of fuel. Even at 40 MPH, coasting in neutral the truck is getting upwards to 100 MPG compared to it coasting in 5th gear at 40 MPH, the truck is only getting about 55 MPG. Interesting...... Of course I am not one for wearing out brakes and having to replace them all of the time, but perhaps the money saved at the pump can buy me new brake pads and have extra change left over

Keep those RPMs down and save some money at the pump!!

BigMike

wa4x4 · « **Reply #3 on:** Mar 20, 2006, 10:31:54 PM »

5VZE in the 98 is getting around 16, no freeway driving, lots of red lights. I am not super light on the gas, but I don't need another speeding ticket so I keep the speeds down. I replaced the air filter and it went up a little bit. I think the cat has gotten clogged, so it may be time for a high flow and a new muffler, hopefully that will raise the MPG to around 17-18. Stupid automatics, with their bad MPG. The Subaru EJ25 got around 23 for me.

BigMike · « **Reply #4 on:** Mar 20, 2006, 11:04:44 PM »

wa, the #1 BEST WAY TO GET MORE MPG is to IMMEDIATELY replace your clutch fan with an electric.

When I got back from Japan I converted to an electric ($10 junkyard) fan and I dished out $100 and bought a high tech e-fan variable current controller (http://www.dccontrol.com/) and let me tell ya, what a WISE decision that was. Not only am I getting MUCH better gas mileage, but of course I have a considerable increase in throttle response and much more power at the higher RPM, where my engine tends to "run out of steam" (4700+ rpm).

I was getting on average, going all the way back to last summer, I have recipts documenting 14-15 MPG. By the time my trip OD was hitting 190-200 miles I was back at the pumps again. Anything more then 200 miles was really pushing it. But the VERY FIRST TANK after installing an electric fan, my OD sky rocketed to 240 MILES!!! It has never since gone below 240 and I always run the trip OD to 250 and then hit the pumps out of habit (I still have about 1.5 gallons remaining).

So I went from 14-15 MPG to (OBD-II scanner proven) 17-17.5 MPG.

That means that in 4 fill-ups with the electric fan, I have gone the same distance that I used to go with the stock clutch fan on 5 tanks! (250 miles x 4 = 200 miles x 5). Where I live it costs me about $35 to fill up. So by the time I hit my 12th tank, the e-fan + controller will have paid for themselves [4 tanks = 200 more miles than before (distance per tank with stock clutch fan) = $35 (price of a tank) for free, $35x3=$105 (apprx price of e-fan setup), so 4 tanks x 3 = 12 tanks].

If that doesn't convince you, then this will:
12 tanks @ 200 miles per tank (pre e-fan) = 2400 miles
12 tanks @ 250 miles per tank (post e-fan) = 3000 miles

That means that in my experience, the time it takes for the entire e-fan setup to pay for itself is exactly the same service interval for my engine. So I experienced the benefits of having an e-fan setup and it fully paid for the cost of itself in just one service interval.

Wow.

And get this, beings that it's still winter weather here, I will drive ALL DAY, yes ALL DAY LONG and the LED light for my Fan Controller will NEVER turn on, not even once! Driving to the freeway, on the freeway, off the freeway driving to college, hunting for a parking spot at the college, heading back home in the warmer afternoon weather, stuck in 5pm traffic, the electric fan NEVER TURNS ON. After the truck has already warmed up, the fan does kick on if you let it idle without moving for more then about 5 mins, and I do not get stuck at a red light for that long.

So I could have just removed the stock clutch fan and been driving all over town, just the same way that I usually drive, without it even overheating. Of course once the weather warms up it will be turning on more often, but it is just amazing to see how much we really don't even need the fan for regular city driving during the winter.

BigMike

wa4x4 · « **Reply #5 on:** Mar 20, 2006, 11:11:36 PM »

Might look into that, I didn't know you drove your truck everywhere...I just assumed you had a DD.

BigMike · « **Reply #6 on:** Mar 20, 2006, 11:16:53 PM »

Quote from: wa4x4 on Mar 20, 2006, 11:11:36 PM

Might look into that, I didn't know you drove your truck everywhere...I just assumed you had a DD.

Well, I have a Bike but I broke the clutch cable back in Jan and I've been to lazy to replace it. My trusty Yota has been my Daily Driver since November of 2004. This is by-far the most reliable mode of transportation that I have ever had. In two years the only trouble I have had is my drivers side rear wheel cylinder went out and my clutch line slowly started leaking at the clutch master cylinder (I over tightened it and cracked the line).

I sure miss my MR2 though..... Sucks putting this many miles on tires that cost so much. When I got the truck it had 62,364.8 on the OD and it now has 82,323.1. In the 15-3/4 months I've daily driven it, I've averaged about ~1,250 miles per month, or about ~15k a year.

Mike

wa4x4 · « **Reply #7 on:** Mar 20, 2006, 11:21:27 PM »

Yeah. I miss my WRX. Only been 3 weeks without it, but still. I got it taken away for speeding, but that's another story. For now the trusty 4runner gets me where I need to go. I need to re-do the brakes badly in it .

85-4roller · « **Reply #8 on:** Mar 21, 2006, 01:08:53 PM »

stock 85 4 runner efi 244k miles 22-25 mpg hwy other ride- 85 runner efi 30 k on rebuild

4:88s w/33s & deitroit 21-24mpg hwy all at speed limits 19-21mpg for both in town

Lonestar Honcho · « **Reply #9 on:** Mar 21, 2006, 03:20:31 PM »

Hey BigMike, you got a web page or something? I sure would like to see the specs and some pics of your truck.
Thanks for posting either way.

wa4x4 · « **Reply #10 on:** Mar 21, 2006, 03:21:25 PM »

Search BigMikes' 81 or something like that, should come up with a nice buildup thread.

Lonestar Honcho · « **Reply #11 on:** Mar 21, 2006, 03:22:32 PM »

Doh, found it. Under his screen name.
Thanks.

BigMike · « **Reply #12 on:** Mar 21, 2006, 04:04:49 PM »

Quote from: Lonestar Honcho on Mar 21, 2006, 03:20:31 PM

Hey BigMike, you got a web page or something? I sure would like to see the specs and some pics of your truck.
Thanks for posting either way.

My Project Thread:
http://board.marlincrawler.com/index.php?topic=4401.0

My wimpy Photo Gallery:
http://board.marlincrawler.com/index.php?topic=6532.0

3RZ Database Thread:
http://board.marlincrawler.com/index.php?topic=19275.0

Jeffe 81 · « **Reply #13 on:** Mar 23, 2006, 07:44:30 AM »

'81 22r with recent timing chain, headgasket, carb rebuild, Marlin tranny, Doug Thorley Tri Y headers, K and N air filter, stock gearing with 31" tires getting 25mpg. Not bad with just under 200,000 miles on the original engine!

84_yota_4wd · « **Reply #14 on:** Mar 23, 2006, 08:31:44 AM »

hey man damn some of u guys r gettin good fuel mileage. mine floppin' sucks ive got an 84 carb 22r with a header some head work ported and 3 angle valve job and springs with dampeners and i only get like 11-12 miles a gallon with 31 inch tires

BigMike · « **Reply #15 on:** Mar 23, 2006, 06:17:50 PM »

I remember our stock '87 4Runner (22R-E) used to average about 17 MPG and Marlin's old carb 22MAR engine used to get 13-14 MPG no matter the load, flat foot or not, it would always get 13-14 MPG.

I believe he is making 16 MPG with his 3RZ right now (his truck is nearly 1 ton heavier than mine

)

kneedownnate · « **Reply #16 on:** Mar 24, 2006, 09:42:11 PM »

THANK YOU BIGMIKE FOR FINALLY PROVING TRUE WHAT PEOPLE HAVE BEEN CALLING ME A FOOL FOR SAYING!!! I've tried saying that mileage is very closely related to rpm for the most part, but have been shot down every time I say it! I proved it in two of my trucks, my brother in his corolla gts. I understand that if you're into the secondaries there's more consumption, but if there's no added vaccuum(low rpm/bogging) then theoretically it's not "pulling" in more fuel. I've also done my own "tests" on the tailgate mileage theory, and have long since felt it's merely a myth that so many people believe. Fill your bed with a layer of leaves/pine needles, then drive around with the tailgate up for a while and keep an eye on them to see what happens, then do it again with it down. Either way they'll end up at the front of your bed, but having the gate down will potentially cause added drag. As the air comes over the top of your cab it rolls over and just kinda boils behind the cab.

wa4x4 · « **Reply #17 on:** Mar 24, 2006, 09:51:40 PM »

My WRX with no clutch fan and 2 electric fans gets around 24mpg and that is with the 2.5liter turbocharged motor, and yes, I like boost. I could get 25+ if I stayed out of it, but why?

kneedownnate · « **Reply #18 on:** Mar 24, 2006, 10:54:16 PM »

My 91 2wd got 29mpg last weekend at a pretty constant 80mph.

rexandfx · « **Reply #19 on:** Mar 26, 2006, 02:15:54 PM »

My 86 22rte runner is gettin 9 MPG, no matter how you drive it. It gets 9 on the freeway, 9 on the freeway pulling a 4x8 trailer packed full. 9 with the trailer empty, 9 in town, and stop and go. 9 everywhere. but I don't drive it, It just has issues.
And to top that off thats on 235/75/15 streets....lol

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