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Some help with current fuel mileage Issues

1K views 17 replies 10 participants last post by  dchawk81 
#1 ·
Currently only getting around 16.9 hand calculated in my 1994 4.3 auto 2WD single cab long bed. My current set up is a SBC 14x3 intake, cat delete and fresh 2.5 inch magnaflow muffler and piping, Electric fan and no more fan pulley. 235/75/15 general grabbers (29.5 tall) on mickey thompson classic aluminum wheels. Stock height truck, auto 4l60E. I have changed spark plugs, fuel filter, oil and filter every 4k, and i drive it easily. I have also taken the spare tire mount and such off to help out with a little weight reduction. Should i switch to a lighter shorter tire to help? Factory tire size is 215 75 15 for the truck, but 235 is factory for the ZR2 and 4x4 models. Truck has right at 100k miles and is spotless. only seen 4 winters and the front end is tight. Just a little confused why its not 20 or more like other 2wd models are. Thanks in advance
 
#2 ·
Your tires and gearing are probably hurting the mileage some. But I don't think a 2wd 4.3 V6 will get in the low 20's unless pure interstate driving at a legal speed. I only get around 15.7-18 in my 2003 truck no matter how I drive it.
 
#3 ·
Next question, does anyone make a turbo kit for these? I mostly work on duramax engines and turbos and i know how expensive those remote mount kits can get, does anyone have a t3 or t4 kit to put like a s363/s366 turbo on these?

I also have contemplated going back down to a 205/75/15 like the manufacturer says on the door, they are 2.1 inches shorter and tire weight goes down by 41 pounds if i switch from a 235 to a 205
 
#4 ·
Lighter tires might help fuel economy around town, but on the highway, it makes little difference.

Tire width does affect aerodynamics at highway speeds.
But taller tires tend make your gearing a bit taller.
There are 235/75/15s out there that weigh as little as 24lbs. each, and aren't as wide.
You usually find these in the lesser known brand budget tires.
The Starfire (Cooper Tires) SF-340 is a good example. The 235/75R15 is about 24lbs each, about 5.6" in tread width, but still around 28.9" tall.

The Falken Sincera SN-250 is another budget priced tire that has an 80K treadwear warranty, has good ride comfort, but weighs in around 30 lbs each, has a tread width around 7".
Probably good for those that don't want too skinny of a tread on their truck.

I don't think you mentioned what axle ratio your truck has. The two most common ratios for 4.3 powered 2WDs are 3.08 and 3.42.
 
#5 ·
I've owned a 1985 Monte Carlo with a 4.3. Drove almost nothing but highway miles. Best I ever got was 19 mpg.
My wife had a 1994 S10 single cab, 2WD, 4.3 when we got married. Best it ever got on the highway was 19 mpg.
We traded the pickup for a 1995 4-door Blazer, with obviously a 4.3. Best it ever got on the highway was 19 mpg.
I now have a 1994 S10 extended cab, 2WD, 4.3. Haven't driven it on the highway any length, but around town it averages 16 mpg.

If you're seeing S10 pickups getting into the 20's on the highway, I'll bet it's because they're either not driving a hair over 50 mph, or they have the four-banger in them.
 
#6 ·
My Sonoma will get between 25-26 mpg with about 70% highway driving, kept at 55mph, but up to 60 at times.

But I do have extensive mods.
Efans, tune, lots of weight reductions, no A/C, early torque converter clutch engagement, ect.
 
#7 ·
my 2002 blazer used to get 18 no matter how I drove. (5 speed manual 2wd) then long story short replaced the coil pack as it showed a weak spark (orange - not blue) and ign control module. instantly got better mpg. Then fuel pump died and just got it replaced last tuesday. my over head console is now telling me 20-22 on the highway on level ground and little wind used to say 16-18mpg constantly. by what ammount of miles ive driven today its deffinately more than 18mpg.

I havent gone thru a whole tank yet to see what my mpg has changed or not. Just filled it up today and i think they didnt tighten a hose clamp or something as it got near the top fuel was running out of everywhere....gotta take it back monday...
 
#8 ·
Did you calibrate the ECM to account for the tire change? If they're not the same diameter as stock, the odometer and tripometer will not be accurate and thus your calculations will be incorrect.

In other words, you're still driving the same distance to work but the truck doesn't know that.
 
#9 ·
Good point. The 235/75 tire is 4.3% larger than the 215/75 so your odometer and resulting figures will be off by that much. When the odometer says you have gone 5280 feet you will have actually gone 5507 feet. In other words 16.9 is really 17.63. So you're actually getting close to 18 mpg. Not bad for a 23 year old 4.3.
You could also try bumping your initial timing about 2°. Those TBI engines don't seem to mind it at all. Especially since you're not towing.
 
#10 ·
General Grabbers aren't exactly a low rolling resistance tire either.

Run the AC/defrost and your mileage drops too.

Low air in the tires? Mileage drops.

Pass people on the highway? Mileage drops.

I get about 19 from my 2001 S-10 2WD 4.3 with 3.42 rear & automatic & extended cab almost all highway to work and back on stock tires. They're some cheapo brand my step grandfather put on for my grandma. The commute is almost exactly 65mph with cruise set and no passing.
 
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