Fuel Mileage poor. How come?

HCO4x4 · Post by **HCO4x4** » Tue Oct 21, 2008 8:15 pm

How can you get around 16 mpg and I'm sitting here at 12?

Post by **HenryJ** » Tue Oct 21, 2008 8:30 pm

Did you recalibrate for bigger tires? What gear ratio do you have? What driving conditions?

HCO4x4 · Post by **HCO4x4** » Wed Oct 22, 2008 4:38 pm

No I didn't but now it makes a lot more sense. Stock gears. Strait flat Florida roads. Know how much a calibration would cost?

Post by **HenryJ** » Wed Oct 22, 2008 4:52 pm

Stock gears does not mean much as there are different ratios available. Read the Deciphering the RPO code list post and see what ratio you have. That may help make some suggestions on what could help.

It is very likely that you are off as much as 10%

That still has you on the low side for mileage, so you might do a tune up and read up on plugging precats.

HCO4x4 · Post by **HCO4x4** » Wed Oct 22, 2008 5:27 pm

3.73 gear ratio

Post by **HenryJ** » Wed Oct 22, 2008 6:06 pm

The tire size will help then. Most of the 3.42 ratio guys seem to be doing fine up to 31" a few over that too.
Most of the guys with 3.73 see increases from the bigger tires.

Try to choose a tire that is lighter weight.
Play with the tire pressure to get the maximum pressure without sacrificing the tread wear. Make sure they are all properly inflated.

A maintenance dose of injector cleaner regularly is a good idea.

Open up the exhaust system from the cat back is a good idea. There are lots of ideas. I can't say any one thing is the answer. It tends to be a combination that works well together. I have spent a bunch of money to maintain only the stock fuel mileage. Many modifications take away while providing performance. I have done what I can to satisfy both.

Less than 14 mpg, usually means something is up. I would look seriously at the possibility of a plugging cat. Either that or lift that right foot once in a while.

HCO4x4 · Post by **HCO4x4** » Wed Oct 22, 2008 6:14 pm

Ok I'll take a look at the precat asap. Thanks for the help

sonomadude4x4 · Post by **sonomadude4x4** » Tue Oct 28, 2008 12:26 pm

will it pass inspection with no precat? and will it make it any louder? or set off any warning lights?

Post by **HenryJ** » Tue Oct 28, 2008 1:35 pm

sonomadude4x4 wrote:will it pass inspection with no precat?

It will not pass a visual inspection. It will pass a sniffer and OBDII check.

and will it make it any louder?

A little perhaps. I really didn't notice much of a difference, but still mine was really bad and had become really quiet as it plugged. So I guess it was probably a little louder.

or set off any warning lights?

No.

sonomadude4x4 · Post by **sonomadude4x4** » Tue Oct 28, 2008 1:58 pm

ok. . . i have noticed my tyruck getting a little quieter and my gas milage sucks. . . im averging 14mpg and thats highway driving back and forth to school

WileyHunter · Post by **WileyHunter** » Tue Oct 28, 2008 2:16 pm

sonomadude4x4,

What you might consider doing, is remove the precat, gut it and weld it back in place... If they look close enough to notice the welding, just say it was replaced...

AZS10Crew · Post by **AZS10Crew** » Wed Oct 29, 2008 7:50 am

Also consider the weight difference between the stock wheel and tire setup and 31" mud terrain tires on aftermarket rims. On just the tires alone there's a 13lb difference between stock and your current tires...52lbs extra all around can make a difference too.

sonomadude4x4 · Post by **sonomadude4x4** » Wed Oct 29, 2008 11:57 am

i have someone that will probly inspect it that wont mind the pre cat not being there so i think ill just get someone to take it off

Post by **HenryJ** » Wed Oct 29, 2008 12:24 pm

Be sure to get a good look at the intake side. If it looks like a clean honeycomb, then we will need to look elsewhere.

F9K9 · Post by **F9K9** » Wed Oct 29, 2008 3:07 pm

HenryJ wrote:Be sure to get a good look at the intake side..........

Wait over 1/2 an hr to examine it bare handed. The muffler shop tech watched me burn the $hit out myself before he advised "it stays hot a long time".

HCO4x4 · Post by **HCO4x4** » Sun Nov 02, 2008 7:00 pm

Well I took the pre-cat out today... it looked clean to me. I guess the clamps i put on to hold the new pipe aren't air tight because it sounds like a POS. I'll have to fix that and see if my mileage is any better but what else could cause such poor mileage?

Post by **HenryJ** » Sun Nov 02, 2008 7:09 pm

Disconnect the battery to reset the PCM.

Do your tune up and check into calibrating the speedometer. At least check the percentage of correction that needs to be applied.

Horsehammerr · Post by **Horsehammerr** » Mon Nov 03, 2008 1:34 am

Maybe you need a new fuel pump. Mine died 3 weeks ago. After playing guess what part # fits, I got the right one . It only took three tries to come up with the fact that I have an 01-02 not an 02-04 model '02. 01-02 has steel tank,02-04 has plastic tank, just FYI. Anyway the topper of this hi-tech story is after going though 5.5 hours of tank removel and 3 weeks of discovery in part # research I'm back on the road and very happy with the results. I went from 22.5 MPG to 25.75 MPG and these are GPS and Interstate Mile Marker readings over a 200 mile round trip mostly up and down the hills of the Ozarks. Same trip today so I'll keep you updated.

HCO4x4 · Post by **HCO4x4** » Mon Nov 03, 2008 7:24 pm

I cant imagine getting that gas mileage lol. Ill try some of your other suggestions. My fuel pump is only 5 months old though.

WileyHunter · Post by **WileyHunter** » Mon Nov 03, 2008 8:43 pm

Horsehammerr wrote: I went from 22.5 MPG to 25.75 MPG and these are GPS and Interstate Mile Marker readings over a 200 mile round trip mostly up and down the hills of the Ozarks. Same trip today so I'll keep you updated.

THANKS

I was happy with my 20-22 mpg on the '03 until I read that. Now I'm thinking I need to spend the $$$ and get a new fuel pump, just to try to get better mileage...

Horsehammerr · Post by **Horsehammerr** » Tue Nov 04, 2008 1:33 am

Well I did the same trip yesterday and still have over half tank left, so I'm going for it again today. I am just blown away 'cause the only thing different is the gas pump. I do run 35 lbs. air front and 32 rear on 275/60/15 s and all that extra drag from my stock roof racks on my '02 ZR5 CC. I read about some of this miledge killing wind drag and wonder where these people get this crap.

Rockrz · Post by **Rockrz** » Tue Nov 04, 2008 7:26 am

HenryJ wrote:It will not pass a visual inspection.

I'd bet that most state inspection guys wouldn't know that a pre-cat is supposed to be on there in the first place, so that shouldn't be much of an issue.

If they ask about that new small section of pipe, just tell 'em that area got damaged and needed to be replaced.

Unless the guy happens to know this type of truck or he goes and does some research, he won't know the difference.

F9K9 · Post by **F9K9** » Tue Nov 04, 2008 5:09 pm

If, it was my livelihood and my agency was known to plant illegal rigs at my inspection location to eliminate state government employees that failed to do their job. I would look hard at each vehicle and have a database complete with photos at my disposal to do my job.

sonomadude4x4 · Post by **sonomadude4x4** » Tue Nov 11, 2008 4:29 pm

my crew cab has 80,000 miles on it so do u think my pre cat is plugged? cause gas milage sucks and it had also goten quieter

F9K9 · Post by **F9K9** » Tue Nov 11, 2008 9:05 pm

Well, what else have you done (tune up related) to it?