What gives these pigs better fuel economy?

[turbovanman]

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?

[thadrawr]

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

[CanukGMC]

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

[turbovanman]

Originally Posted by thadrawr

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.

[turbovanman]

Originally Posted by CanukGMC

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

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

[dwausa]

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

[tkz22]

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

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

[ChrisGood]

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

[jdmccright]

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!

[excheezhead]

Originally Posted by turbovanman

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!!

[turbovanman]

^^^^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,

[excheezhead]

Originally Posted by turbovanman

^^^^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,

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!!!

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

[jdmccright]

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...

[turbovanman]

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.

[Babs007]

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.