So...didn't mythbuster's prove that a tailgate that's up will do better than down? I mean, I don't think it would really change that much, but I believe that the tailgate up is the way to go.

 

Yea I remember something about that. Very minimal to no change in MPG I think.

 

I mix my own high octane fuel for another vehicle I own, which requires 93 or higher. My mix brings it up to about 96, and it runs very well on it.

But, I wouldn't run 93 in the truck, unless it's been modified a bit...cleaners are the only thing I put in the tank with the gas.

The car i run the specially mixed fuel is an AMG tuned Mercedes 560SL that ran 162 at speedweek last year in Utah. She won't run right on 93 pump...she's a finicky woman.

 

See that's the thing, when I run 87 it's slow and hesitant, but as soon as I give it 93, it flys and roars! Maybe the PO did something? Not me, the only thing I have done is the K&N Air Filter Drop In!

Weird huh? And when I say roar, I mean big difference ROAR!

 

K&N cold air? because those don't do crap for these trucks

 

Here's the deal...go to a paint store and pick up a gallon of toluene. Mix it with your gas at a 10% concentration. You'll end up with 94.2 octane fuel. If you buy it like I do, wholesale, it's cheaper than paying for 93 octane fuel.

10%...94.2 Octane
20%...96.4 Octane
30%...98.6 Octane

 

First things first......you can't get an accurate MPG calculation unless your odometer is correct. If you have 30" tall tires, my guess is they're taller than factory. If so, you're getting better MPG than you think because you are actually travelling farther than the odometer indicates (providing it is indeed off). Use the search function in this forum to find out how to calibrate your speedo based on your actual tire. It's very easy and only takes a few minutes.

If you do have an exhaust leak close to the o2 sensor, it can throw the sensor's readings off and can result in a rich mixture. Exhaust leaks can also effect low RPM power, which can hurt MPG as well. IMO, you should be able to get better MPG than you do, if everything is working correctly and in a good state of tune. I can pull down 17-18 with my 5.8L F250 consistently, but it's also a 2wd regular cab XL and fairly light compared to an extended cab 4X4. I track the MPG on all my cars on a regular basis. It is a great indicator of developing mechanical problems before they can be noticed by drivability.

 

Didn't you say that you think the cat is clogged? That'll kill MPG for sure.
X2 on the correct tire size calibration as well. Your truck's computer still thinks it has stock tires on it.
High octane fuel is more resistant to detonation, and will combust at a slower rate. I've always been told run only as much octane as it takes to combat detonation. In other words, only high compression motors or those w/ ignition timing overly advanced need higher octane. Not sure why your truck would run better with 93?

 

Is this safe? I just wanna double check, but will most definitely be doing this if it is!

 

Not sure why it does with 93, but man I tell you, no bull, it gets a wake up call.

Also I think the cat is clogged because I here like a put, put, put, put, coming from the cat, so I just guessed that, but it could be the exhaust leak, either way I think I'm going to delete the cat. Maybe even a high flow cat.

Umm, how do I recalibrate the odo. and speedo? And I think it's the same height, but I actually think my tires look skinnier than stock ones.

 

at about 80% highway (65mph) my 88 consistently got just over 18 mpg. although now the average is down to about 16 since I put a set of 32x11.50 muds on it. and even with those it was able to get 14 driving up and down colorado mountains for two days. and yeah, im the kinda guy that double checks the odometer to gps, and uses the same pump whenever possible so that the truck fills the same every time (and i never go past the first click)

5.0, m5od, 3.55's extended cab longbox, still has all (and i do mean all) of its emission equipment. egr, smog pump, both cats. has a drop in K&N, electric fan, and the exhaust disappears about 3 feet after the cat, and its possibly clogged too, cause its every bit as quiet as a factory truck.

the biggest thing is the way you drive. I embraced progressive shifting, hardly ever drove over 65, and generally got passed by everybody while accelerating (in which you want to give it just enough throttle that its accelerating, but not so little that your just wasting time) i never did install one on the 88, but a vacuum guage is the best 20 bucks you could spend on fuel mileage

as far as work to the truck goes, do a full tuneup. no platinum plugs either. get autolite coppers and side-gap em'. change the oil in your tranny and diffs, grease your u-joints. change and adjust the wheel bearings, make sure the brakes aren't dragging, make sure your tires are inflated to the max thats on the sidewall. rather than bothering with cleaning the egr, just go get a new one and make sure the vacuum lines are all good. and as said above, an exhaust leak, even after the o2 will mess with its readings. make sure that you

check your timing. if its too far advanced and its getting slight detonation, the higher octane would "fix it" and make it seem more powerful. your pretty low in altitude, so you shouldn't need to crank the timing too high. high octane fuel doesn't do crap for power or economy unless the engine is built/tuned for it. and like the acetone craze a few years ago, the only benifit was on vehicles with horribly dirty fuel systems that it cleaned out. I would only use seafoam when doing the vacuum line method or with an injector cleaning machine. every year or so i usually just grab a can of bg44k to do some cleaning and lubrication and call it good. marvel mystery oil would work for that too, I have used it in the crankcase of engines that have sat for a while, its good for sticky lifters too.

walk out and rub the tread on your front tires, if it feels like the tread blocks are "sharper" in one direction than the other your toe-in is out of alignment and it is literally plowing the tires sideways down the road as you drive. an alignment would fix it. I have seen many vehicles (including my 88, which i did with a tape measure!) that have gained mileage. my dad had a little gmc safari that jumped 3mpg after an alignment (but it was pretty bad to start with)

if your worried about the tailgate, just go get a tonneau cover, you can even build one for fairly cheap.

the guys over on FSB have claimed good results from building a new Y-pipe for the exhaust, getting rid of the horrible bends in it. this and a set of shorties would work good. its on the list for mine, I just got a set of pacesetters the other day.

another item that would help would be a set of underdrive pulleys, if it has trouble staying cool its a lack of cooling system maintenance.

if you really want to push it, get a bigger radiator, and run one of these grill blocks meant for winter, and slowly close off the grill until it starts to run on the warm side, then open it back up to where it was ok, install some heat extractors in the hood, and build a fastback tonneau cover, then go and buy some prerunner fiberglass body parts.