Hey Y'all

[GasSavers_BEEF]

is your mileage adjusted for your larger tires?

many times people don't worry about doing that and their mileage is better than they think because they don't adjust. it may not be huge but there again, your goal isn't that far away.

[Jay2TheRescue]

That's a lot of oil usage. I would use a conventional 10W30 in it, coupled with a set of spark plugs 1 range hotter than stock to help keep them from fouling. Take your plugs out at every oil change, clean them, and check the gap. Check your underhood emissions label, I believe your plugs should be at 0.045" if my memory serves correct.

Driving a 350 like you got an egg between your foot and the pedal does not work. I've found its best to just give it about 20-25% throttle, get into overdrive, then feather the pedal. When driving, stay within the speed limit, as aerodynamic drag gets exponentially worse the faster you go, and those trucks are about as aerodynamic as cinder blocks.

On mine I noticed that it pretty much gets the same mileage with the a/c on or the a/c off. I think this is because in the grand scheme of things, the drag of the a/c compressor is nothing compared to the output of a 350. Run the a/c when you feel you need to, as the aerodynamic drag of riding with the windows open will take a bigger hit on economy than the a/c will.

For general driving, without getting into advanced techniques, using the cruise control is going to be better for fuel economy than driving without it.

Your engine and computer system probably have Decelleration Fuel Cut Off (DFCO), but I would not recommend trying to aggressively implement DFCO as a fuel saving measure. I tried this on one of my trucks, and it worked - beat the EPA highway rating driving in the city, but it cost me about $1,200 in transmission repairs a couple months after I started doing that. The best use of DFCO is just to let off the accelerator on hills, and let the truck coast down. If you're going fast enough, the computer will shut off the fuel injectors. Under which conditions the injectors will shut off will vary from model to model. On my truck, the injectors shut off if the RPM > 1,500 and you lay off the throttle for > 3 seconds. The injectors come back on when either I press the accelerator, or RPM < 1,000. These conditions can be coaxed by downshifting at lower speeds when stopping anyway (like at traffic lights), but like I said, with the age and mileage of your vehicle I do not recommend this strategy.

When on the highway, drafting is an excellent strategy. DO NOT attempt "NASCAR Style" drafting though. We're not talking about being 2 feet from the rear bumper of an 18 wheeler. Its amazing how far back you can follow a tractor trailer, and still see a measurable increase in your fuel economy. Look at the striped lines marking the highway. I recommend following no closer than 3 stripes. I usually try to follow about 4-5 stripes behind when I draft. Settle in, match the truck's speed, and set the cruise. Pay attention, as the truck may speed up or slow down, you don't want to run into the back of the truck.

If you have one of those plexiglass bug shields on your truck, I'd recommend taking it off. I had one on my 86 Chevy when I bought it, got a 2 MPG increase just by taking it off.

[theholycow]

I'll second what BEEF said about calculating your fuel economy; if you have oversized tires and aren't calculating in the difference then you're already getting better FE than you think. There are plenty of tire size calculators that can tell you a percentage speedometer difference; add that percentage to your miles when calculating your FE.

Around town, try to avoid stopping at red lights. As soon as you know there is a red light ahead, slow down immediately. Your goal is to arrive at a fresh green light going as fast as possible instead of stopping at a red light.

Also, roll up to turns rather than cruising up and then braking. (Whether you neutral coast, leave it in gear with your foot off the pedal, or downshift to try for DFCO is up to you.)

In general, any time you can avoid using the brakes, you've just avoided discarding energy. That's energy that you spent fuel to make, and that you'll spend fuel to make again.

Never do any of this if it will compromise safety. Safety comes first.

[CaineRaisenBlazer88]

Beef: I have not put the larger tires on the Blazer yet, I still have stock size tires that are DINKY! 31" bfg at's that are wore so its like having a 30 But the 33 Duratracs I am going with weight just 6-7 pounds more a tire, I think they weigh 48 a piece and 31 bfg's weigh 42, so takeoff should be mostly preserved and the engine not have to work as hard to turn them, if I am thinking right.

Jay: I might try the spark plug idea, I run regular AC DELCO's, whats the next grade up, the platnuims? and mine are to be gapped at .035, but would it run better with a .040 with the hotter plug? I have found the same thing about the throttle thing bo! My mama gets on me for not babying it all the time, but I know not to cuz it gets better mpg, but she cant understand I took my A/C off. Well, I took the belt off, the compressor is still there, but the motor is freed up a bit so maybe a extra 2 HP haha! I cant use cruise control effieciently due to a blown torque converter. I haint had OD in over a year, but I still pull close to the same, about 1-2 mpg less, but its getting fixed asap! I have never heard of DFCO on a Blazer, but I will ask on the Blazer forum and get a answer. Going back to the TC, I do not get on the interstate to much to try this, but I will when it is fixed and no bug shield here, they are ugly as sin on Blazer anyway.

Holycow: Many good points you bring up there, all of which I try to do with safety in mind. What are some advanced things I can do? I'm going to seal off the front of my beast, but first im putting in a bigger radiator that I pull out of one of my daddy's ol 84 GMC, its nearly twice as thick as the one in there now and it should cool the motor down more efficiently. I'm making a shield to go under the engine, but i am lost on the materials to make it out of. Y'all got any bright ideas?

[theholycow]

Tire weight isn't as important as you might think; other variables are much more important. Unfortunately the most important variable isn't tested or published for most: Rolling resistance. Those aggressive Duratracs probably have more RR than BFG AT's. Then there's just the fact that they'll be new and replacing worn tires; worn tires have less RR (so better FE). I'd accept that loss, though, for those awesome tires!

For explaining the moderate acceleration, consider the torque converter. Its job is to waste energy, turning work into heat. You can slosh it for 1/2 mile as you gently gain speed before you cruise, or you can slosh it for a 1/4 mile and then cruise efficiently. At some point, the extra RPM and enrichment required outweigh the loss in the torque converter; the middle ground is where your FE is.

The Blazer forum probably won't know how your Blazer's DFCO behavior is. Realistically, I suspect your 1988 GM is equipped with TBI, and I doubt they ever programmed TBI to DFCO...and I bet the company that provided your aftermarket chip didn't bother with it either. Don't count on DFCO.

Another driving strategy I thought of after posting was dealing with stop-and-go traffic, either the small annoyance leading up to a stop sign or the big annoyance in a highway traffic jam. Try to idle along with a bunch of space in front of you instead of gas-brake-honk-brake-honk-gas-brake-head explode-gas-brake-honk. Either way your average speed is 2mph, might as well roll smoothly.

Grill blocking may help, but I can't say I've ever managed to measure a real effect. Luckily it's free so it's worth experimenting with just in case it works, and it still provides quicker warm-up in winter. There's no need to upgrade your radiator; it's not all-or-nothing, you block as much as you want.

For the belly pan, you may not need to reinvent the wheel. If you can find a pre-fab skid plate for nearly free that is smooth and has good coverage, you have a winner. Otherwise, the most popular material is coroplast, the corrugated plastic material used for campaign signs and road spam. You can collect road spam/used campaign signs, or you can buy nice large sheets of it from sign companies.

A plastic bedliner, easily found for free, could be a nice piece of material but I'm not sure if the exposed corrugations would eliminate any advantage it creates.

[Jay2TheRescue]

An 88 Blazer gapped at .035? I think that's the stock gap for a points type ignition on 74 and older GM V-8's. I'm pretty sure if you checked your emissions label under the hood, it will say .045. I'm quite sure the gap on my 86 Chevy is .045. I could be wrong though. They may have also changed the gap when they added fuel injection. Anyway, buy AC Delco plugs, ask for one range hotter than stock. Don't mess with Platinums. Just get the copper plugs. The electrode on the platinum is so thin, it might foul easier, plus with as much as you're going to be taking these plugs out and cleaning and regapping them, copper is the way to go. You can just have at a copper electrode with a bit of sandpaper or emery board to clean it. You can't do that with Platinums without risking damage.

Get your torque converter replaced. Not being able to lockup your torque converter, and not being able to access overdrive not only effects your mileage, but will eventually kill your transmission.

DFCO isn't something that most folks know about, but it is an integral feature of almost any computer controlled fuel injection system. When going down steep hills, the computer shuts down the injectors. This helps the vehicle meet emissions standards, saves a little bit of fuel, and since its using the compression of the engine as a brake, you don't end up going 80 MPH at the bottom of a hill. Have you noticed a slight surge in power for a brief instant when first touching the accelerator after gliding down a hill at highway speed? That's your fuel injectors coming back online.

[CaineRaisenBlazer88]

For an aggressive tire, the duratracs have low RR from what I heard, not the level of a michelin, but better than a super swamper. Im with you, they are one sweet, rugged looking tire!

Your explaination of the torque converter confused me. What do you mean "waste energy"? I thought that TC provided a direct power transfer in automatic trannys, prevented slippage ( not good), and preserved 4th gears bands. Maybe I've missed something...

The next chip I get WILL have DFCO on it! I'l make shure and get it programmed into the chip, it sounds possibly like a great FE booster.

Thanks for the all the tips! You've got my brain to thinking, which is both a maricle and potientially dangerous....

[Jay2TheRescue]

Energy is wasted because of the fluid coupling in the transmission. Your economy comes from the TC locking up at highway speed to provide a 1:1 ratio between the wheels and the motor. With a non functional TC, some energy is lost in the transfer of power to the fluid, and back to the wheels.

[theholycow]

Originally Posted by Jay2TheRescue

DFCO isn't something that most folks know about, but it is an integral feature of almost any computer controlled fuel injection system.

I don't think it is as common and universal as that. I think it is not present on TBI systems, for example. My TBI 1987 Cadillac never showed it on its instant FE display, not as 999 or 0 or -- or anything...it just showed constantly changing FE that you would see without DFCO. Also, I imagine that an aftermarket chip for a TBI would especially not have DFCO. I really wouldn't expect this vehicle to have DFCO, although it's still worth checking with a meter.

Originally Posted by CaineRaisenBlazer88

Your explaination of the torque converter confused me. What do you mean "waste energy"? I thought that TC provided a direct power transfer in automatic trannys, prevented slippage ( not good), and preserved 4th gears bands. Maybe I've missed something...

Imagine two window fans aimed at each other, turned off. You turn one fan on. It blows against the other fan, which begins turning. That is how a classic torque converter works. It allows your transmission to be in gear while the vehicle is stopped, without letting the engine stall. It's also what lets your engine RPM vary while your road speed remains steady, for example as you climb a hill. It's also what lets you rev it up a little in gear while trying to pull something that's stuck, like a tree stump.

Your 1988 model almost certainly has a locking torque converter (aka torque converter clutch). It works the same way, but it's also got a clutch in it (similar to the clutch in a manual transmission) that locks both of those metaphorical window fans together, allowing no slippage. The computer locks the torque converter when you're cruising in overdrive (and maybe under some other cruising/light throttle conditions).

The next chip I get WILL have DFCO on it! I'l make shure and get it programmed into the chip, it sounds possibly like a great FE booster.

It's a minor help. Here are the options for deceleration, assuming your vehicle/traffic/safety all support them:

1. Neutral coasting. This uses as much fuel as it takes to idle.

2. Engine braking without DFCO. This uses more fuel than idling because RPM is higher. The closed throttle means that it uses less fuel than the same RPM would with an open throttle, but it's still more than idle. I measured it once and it seemed pretty linear; 2x idle RPM with closed throttle used 2x fuel.

3. Engine braking with DFCO. This uses no fuel.

Note that "engine braking" doesn't mean you're getting thrown forward in your seat like you just downshifted to control speed going down a mountain...when you're in gear, above idle RPM, and off the throttle, you've got engine braking even if it's just a little bit.

Deliberately trying to leverage DFCO is often worthless and sometimes uses more fuel due to inconsistent DFCO behavior, inefficiencies in downshifting, etc. An experienced hypermiler with the equipment to program his own vehicle could probably make it work...I wish I could afford EFILive for my truck.

Thanks for the all the tips! You've got my brain to thinking, which is both a maricle and potientially dangerous....

[Jay2TheRescue]

Originally Posted by theholycow

I don't think it is as common and universal as that. I think it is not present on TBI systems, for example. My TBI 1987 Cadillac never showed it on its instant FE display, not as 999 or 0 or -- or anything...it just showed constantly changing FE that you would see without DFCO.

My mother's 88 Chrysler LeBaron used to read 99MPG (the display's maximum) when coasting down hills in gear. I suspect it may have had DFCO.