What gives these pigs better fuel economy?

It sucks, plane and simple. I have a 98 4 door Jimmy, 4x4, auto. I average 300 km's to a tank, which averages aprox 15 mpg????? The oxygen sensors are new and working properly, I have a K@N air filter, Aurora plug wires, 2.5 inch mandrel bent cat back with a Flowmaster, tires at 40psi. No matter what I do, it sucks. It used to get 375 to a tank but one day, it just dropped and I can't get it back. I noticed my DIC dips down to 4mpg when accelerating from a stop, even if lightly leaving the line and it has a wicked flat spot around 2000 rpm? the MAF sensor checks out fine, even tried a known good one.
Will a programmer help? Grannatelli MAF?

I would check the brakes....there is a thread over on the Blazer forum about it.

My jimmy averages about the same, it's better on highway (much much better) but in city I avg about 300-350km's per tank. Highway I avg much more, I was getting about 550-almost 600km per tank. It does suck, but hey it's still better than alot of trucks on the road, what's an h2's rating? 8mpg? rofl. I know someone who just bought a BRAND NEW (23km's on the odo) ford ranger and she got 300km's to her ENTIRE gas tank on the highway lol, her engine is only a 4.0l v6, brand new, and gets half the mileage my 120,000km 4.3l vortec gets. Gotta laugh at that one :D

I would check the brakes....there is a thread over on the Blazer forum about it.

Nope, they have been checked and they don't have the rubber bushings, it has 4 wheel disc.

My jimmy averages about the same, it's better on highway (much much better) but in city I avg about 300-350km's per tank. Highway I avg much more, I was getting about 550-almost 600km per tank. It does suck, but hey it's still better than alot of trucks on the road, what's an h2's rating? 8mpg? rofl. I know someone who just bought a BRAND NEW (23km's on the odo) ford ranger and she got 300km's to her ENTIRE gas tank on the highway lol, her engine is only a 4.0l v6, brand new, and gets half the mileage my 120,000km 4.3l vortec gets. Gotta laugh at that one :D

It doesn't get much better on the highway either, :sunglasse

heh, my jimmy has given me 18MPG+ ever since i got her in 96. 155,000 miles and going strong.

My Jimmy ('98, 4dr, 4x4) has 155000 miles. I just got back from a trip, and it got 25mpg on the highway :grinyes: I get between 17 - 18 mpg in detroit!

I have really been lucky and had no problems with bad mileage.

My 2000 Jimmy gives me 16mpg in town and 16 - 18mpg highway... Its the nature of the beast if you ask me, it likes to slurp up the fuel. If it makes you feel better the car in my pic is my daily driver and it also get 16mpg and is premium unleaded only... however highway it can get around 30

Mine's a '96 with 150k miles. I noticed mine getting difficult to start sometimes and also was getting ~15 mpg. I did a fuel pressure check and was showing 55 psi prior to start up...just barely within spec. I changed the fuel pressure regulator and the starting problems went away and am getting 18-19 mpg in mixed driving. If you don't mind a long afternoon under the hood, it is a lengthy process to get to it inside the plenum. I went ahead and cleaned all the sludge build-up from the intake, inside the plenum and the injector assembly (make sure you plug up the intake ports with cloth so that dirt/crud doesn't fall in!). I haven't bothered to measure the fuel pressure after the changeout since it is kind of messy. I'll edit this post when i do. (04-Jun-2006: measured fuel pressure at key-on to be 58psi and 52-54psi at engine idle). Hope this helps!

It sucks, plane and simple. I have a 98 4 door Jimmy, 4x4, auto. I average 300 km's to a tank, which averages aprox 15 mpg????? The oxygen sensors are new and working properly, I have a K@N air filter, Aurora plug wires, 2.5 inch mandrel bent cat back with a Flowmaster, tires at 40psi. No matter what I do, it sucks. It used to get 375 to a tank but one day, it just dropped and I can't get it back. I noticed my DIC dips down to 4mpg when accelerating from a stop, even if lightly leaving the line and it has a wicked flat spot around 2000 rpm? the MAF sensor checks out fine, even tried a known good one.
Will a programmer help? Grannatelli MAF?
WARNING!!! on my 01 jimmy 4.3L wcode, i have tried granitelli maf(3), Jeggs mafs(2) and all of them caused serious problems, really bad gas milage, p101,102,401,751 codes, backfiring, power loss, most all at the same time. if anyone has had any success with after market re-done mafs for a newer 4.3L let me know, cause they don't work on my truck. the best performance AND fuel bump i have gotten was a flowmaster cat-back and the K&n FIPK gen II airfilter charger system, so it could breath better. the hypertechPPIII gave a hint of gas milage bump, but only on 87 octane setting and removing all lead from right shoe. I have a club discount card from costco so i run it on 93 octane, as i can get 93 premium for 10-20 cents cheaper at their pumps.
the 93 setting, i pushed the shifts to 1-2 +2mph, 2-3 +2mph and 3-4 +1mph, and used the tire height as per the formula from dunlop for total in inches, and added the shift firmness opt. i am still getting 16-17 combined in miami fl traffic and 22-23mph on hiway only.
if i pet the lead back in my right shoe, the performance improvment is rally fun, but the wallet yells at me, so i try to keep it easy.
good luck, you have a good start and my personal advice is stay away from spacers and performance MAFS. i've never heard of the plugs you are using, but the best i have luck with is ac/delco rapid fire's.
and remeber, keep your stick on the ice!!
:icon16:

^^^^Thanks for the info. Guess I forgot to let you know, I am a mechanic, smog shop certified and I own my own shop so trust me, I have gone thru every thing on this truck. Tried different plugs and found the G-powers the best for life but will be using Iridiums when these wear out. I also have Aurora wires on, the best in the world and will be putting one of there coils on next week. I actually did try a spacer and I got better fuel economy, I picked up 3-4 mpg but like I said, one day, it just stopped getting high teens and early 20's. Its weird, its like I hit 120,000 km's and a switch went off in the computer to give me shitty fuel economy and a flat spot in performance, :screwy:

^^^^Thanks for the info. Guess I forgot to let you know, I am a mechanic, smog shop certified and I own my own shop so trust me, I have gone thru every thing on this truck. Tried different plugs and found the G-powers the best for life but will be using Iridiums when these wear out. I also have Aurora wires on, the best in the world and will be putting one of there coils on next week. I actually did try a spacer and I got better fuel economy, I picked up 3-4 mpg but like I said, one day, it just stopped getting high teens and early 20's. Its weird, its like I hit 120,000 km's and a switch went off in the computer to give me shitty fuel economy and a flat spot in performance, :screwy:

fuel injector pressure good? possible gunk build up in intake/exhaust journals, cat plug'd, if all that is on spec, man, your the pro, don't trash it build it!!
paxton/edelbrock/nos, screw the mpg's!! bush needs our money to buy the country when he retires!!!:evillol: :evillol: :evillol:

seriously, good luck, but you mpg's ain't that bad.

You might note on my teeny pic that I've removed the roof racks from my truck. Then filled the holes with plastic expander fasteners and are sealed with silicone. That way I can removed them when I need to but will prevent water intrusion otherwise. I have a Flowmaster cat-back system too, but no noticeable change in performance or mpg. I try not to run the AC if I can bear it and keep the tire pressures in check with the air temps. Driving habits are a BIG factor as well. I start out easy, trying to stay around 2000rpm until I'm up to speed and kick into OD. Watching traffic ahead, I can coast and time it so I don't have to slow down as abruptly.
One thing I'm sure that has helped in all of my cars is using Microlon engine treatment. It's more expensive, but it treats the WHOLE drivetrain and fuel system and is a ONE SHOT deal. Not like the crappy Slick 50, et al, that you have to buy every oil change. Gives me an extra ~1-2 mpg. Check out the website and let me know if you have questions. www.microlon.com
I'm also considering converting to an electric fan setup to release a few ponies from that damned fan clutch. Every little bit helps...

Thanks. I don't know if you want to bother with the electric fan. If your clutch fan is working properly, it won't eat any power, and it keeps the engine at a more constant temp. An electric fan will be on more and will eat HP due to the alt having to work harder to make it run. My .02 cent. :2cents:

I've got a 2001 Jimmy 4x4 and my gas milage is 23 mpg city/30 mpg hiway.
It is the most fuel efficient at about 120-130 km/hr. No special parts, all original factory. Good luck with yours.

I own a 96 Jimmy. I was getting 13mpg. I spent $500 on tune up and fuel repairs. It increased my mpg to 16. I was under my vehicle messing around and noticed that the front diff was locked in (drive shaft didn't spin freely). I checked on my friends 98 blazer and found hers was not locked in (drive shaft spun freely). My Jimmy was not engaged in 4X4. I had it checked ant the engaging cable for the front end was broken. $450.oo fix. Now the Jimmy is getting 21mpg.

My fiance is driving it now, she's averaging 20 mpg, so maybe she's lighter on the gas than me??? I also installed a cold air intake so we'll see if I can squeak out some more.:grinyes:

Old thread, yes. But MPG's are near and dear to my heart. :) I was under the impression that a CAI would improve power, but not necessarily MPG's? I thought that warmer air coming in would improve the fuel economy?

My truck is a 2000 GMC Jimmy, 2wd/4dr with 125K miles. I haven't done anything as far as performance parts goes, I just really baby the truck. Has stock intake/exhaust, standard OEM brake replacements, new sealed hubs. No throttle body spacer, or performance chip mod. I have made several trips recently from Mississippi to Michigan, roughly 1100 miles one way. I normally get about 270-290ish miles to the tank between fill-ups on the highway. My latest trip, I went 346 miles between a particular fill up. The next fill up came at 300 miles, with no real change in driving habit. I kept cruise control on both times as much as possible. Being a man, I'm by nature fairly OCD(obsessive compulsive) so I was watching my RPM's like a hawk. My RPM's stayed fairly stable at about 2100-2200, excluding random speed ups to pass or hills here and there. I have no explanation why there was such a dramatic difference in fuel economy between the tanks. I'm leaving again this coming tuesday from Michigan to Mississippi, so I'll try to get a more thorough picture of the travel and post it(ie-outside temp, road conditions, accessories running, night-vs.-day travel, PSI in tires[supposed to be picking up new wheels/tires on monday, so guessing that may affect mileage too])

A bit late on the reply, but here it is:

Excluded the drive between Detroit and roughly Tennessee, since it was snow/ice, the other lengths afterwards I only averaged 300miles per tank. It was pretty much all night driving, with outside air temp being in the 30's until I hit Mobile, which is directly on the gulf coast, and even then, it only warmed up to the mid 40's. I never once had the pedal floored to pass a vehicle. I specifically only passed people on my cruise control, and if I had to slow down, I consistently let my cruise catch me back up to speed, so that the acceleration was controlled by the comp., and not my foot. I'm still keeping an eye out in city driving for habits or conditions that improve/impact my MPG. Nothing noticeable as of yet, except for keeping my RPM's at or below 2K as much as possible.

Thread is almost 2 years old. Using the cruise under daily driving conditions will most likely not improve fuel economy. The computer uses to much fuel to bring the truck back up to speed. A person is capabile of using much lighter throttle inputs.