Post Precat Removal and gas mileage

green02crew · Post by **green02crew** » Fri Dec 19, 2008 1:18 am

Ok so change from last tank to this tank: 1.2 mpg increase. Could be contributed to many things but same driving style, same routes, pretty much same weather too. Not a huge difference but I'm almost up to 13mpg! I don't know why my fuel economy sucks so bad. Only thing I can think of is the tires?? It is city driving but still.

Sounds slightly better but thats about all I'm getting for difference. Worthwhile mod since it was only a couple bucks and easy/quick to do.

Post by **HenryJ** » Fri Dec 19, 2008 7:01 am

Is your speedometer calibrated correctly? Mine was off from the factory.

YellowCrewCabber · Post by **YellowCrewCabber** » Fri Dec 19, 2008 8:37 am

Don't mean to hijack but this got me thinking about comparison. City driving I can get around 230 to 240 miles on a tank. (That's pushing it)I am running 235/70 size tires on mine with no other mods. Speedo has not been recalibrated. Occasionally the police will set up portable "radar bots" to let you know how fast you're going. According to the radar my speedo is accurate.

Post by **HenryJ** » Fri Dec 19, 2008 9:03 am

I may end up splitting this topic, but it is a good subject. Mine came with the optional 235/75-15 tires and was off nearly 5% IIRC.
A GPS works ok to check and the mile markers with a stop watch works too. It really is worth checking. I though mine was getting really good gas mileage, until I straightened out the speedometer. Then it was back to the norm.

green02crew · Post by **green02crew** » Fri Dec 19, 2008 12:51 pm

I go by the scangauge, it was set to tire size and verified by GPS.

border man · Post by **border man** » Fri Dec 19, 2008 8:05 pm

I switched to 30 in. tires, and now my speedo is dead on.

green02crew · Post by **green02crew** » Sat Dec 20, 2008 5:07 am

It depends on which tires I have on, my pcm was reprogrammed and is accurate on one set not the other, this is the accurate set sadly. I still go by the scangauge and verify with mileage reading.

Post by **HenryJ** » Sat Dec 20, 2008 5:16 am

Scangauge is only going to read what the PCM tells it. It will be the same as the speedometer.

kwalsh · Post by **kwalsh** » Sat Dec 20, 2008 6:34 am

I had the same experience with the 235/75-15 OEM, the speedo was off.

Post by **HenryJ** » Sat Dec 20, 2008 7:09 am

It is almost like they over compensated with the recalibration. I was showing over 20 mpg regularly. I came down to reality when it was corrected.

roadrunner · Post by **roadrunner** » Sat Dec 20, 2008 1:02 pm

Just returned from Denver yesterday. Avg temp 25F winds quartering (running East on I 70) from SE at 10-15mph speeds consistently limit plus 4mph (all 70-75mph range). Average mpg for return trip verified by mile markers, trip odometer, and scan gauge with gas measured in sitting in same position 21.8mpg. Miles, speeds, gallons used, and distance were consistent between actual and scan gauge recordings. Truck is stock except for noted mods on my sig line. Tires are 235x75x15 BFG AT KO's @50psi cold. This trip from there to my home is an altitude drop of 2300 ft. The trip out there under very similiar conditions (temps were lower by 20F) yielded 16.78mpg. I realize the tire pressures seem high but they are rated for it and my mileage suffers if I drop much below 45psi. Enough I can notice the difference anyway. There's my .02 worth.

Post by **HenryJ** » Sat Dec 20, 2008 1:04 pm

Don't mess with perfection. That is very respectable.

F9K9 · Post by **F9K9** » Sat Dec 20, 2008 1:30 pm

Can we please stop talking about our MPGs? I have been depressed enough with mine. Thinking about how that I could have spent the $400 that I would have saved if, the prices were this cheap 2 months ago when I went to Moab.

roadrunner · Post by **roadrunner** » Sat Dec 20, 2008 1:33 pm

Hey Reed! That just makes the "experience" all the more precious. At least you got to go.

YellowCrewCabber · Post by **YellowCrewCabber** » Sat Dec 20, 2008 1:41 pm

Yeah Reed, what he said.

green02crew · Post by **green02crew** » Sat Dec 20, 2008 1:46 pm

HenryJ wrote:Scangauge is only going to read what the PCM tells it. It will be the same as the speedometer.

The scangauge has a tire size setting. You can set it by the percentage the tires you are using are smaller or larger than the stock pcm setting. You can also verify it by gps as the scangauge gives a readout of mph while changing tire size so you can set it by mph on the highway as well. Makes the scangauge tool more accurate than the pcm.

Post by **HenryJ** » Sat Dec 20, 2008 2:30 pm

You are correct. It can be calibrated. You did not mention that you had done that, or I missed it.
You can also alter the settings for the stock readout with a power programmer or custom flash of the PCM.

I tune mine with the HPPIII.