When I first got my truck with 93k on it I changed plugs, trans fluid, PCV valve, u-joints, O2 sensors, oil and filter, and cleaned the throttle body. I have also added an exhaust cutout, a new muffler to replace the old one that rusted through, a cold air intake, and did a small torsion bar crank. Well mid summer I made a 3 hour drive from Novi to Muskegon and averaged 16.5mpg on the overhead computer which I was happy with.

Since then I drove the truck from Novi to ******* (about 3 1/2 hrs) and averaged 14.5mpg which was understandable with a bed full of gear, a hitch carrier, and a cab full of people. Now I drive from Kalamazoo to Novi (about 2 hrs) regularly with just me in the truck and I can get any better than 14.5mpg. I tried going 75 then 80 just for the hell of it and it only got worse. Now I keep it on cruise at 70mph all the way and the mileage is just terrible, especially after owning a Bonneville that averaged 30mpg on the same trip. The truck has the 3.92 gears in it, which I'm sure doesn't help. It's also missing the air dam, not sure if that would help or not. I know it's not made to be efficient and I love the truck either way, just wondering if theres something I can do to help it.

 

Two things,

1) never trust the overhead console. Calculate your mileage my hand when you fill up
2) SO SO SO many things determine MPG. On top of that, resetting the PCM to delete the short term and long term fuel trims can help because the truck s PCM learns your driving habits and adjusts accordingly.

 

I used to do it by hand but only around the city when mileage was in the 12's. I thought the overhead console would be close enough to see a change in mpg's even though they're not accurate, maybe thats not the case. I have been driving agressively lately in the city at least, will resetting the pcm help then if I change my driving habbits?

 

OMG!! You mean using real math?! What a concept! I drove mine down to Ocala last Saturday for "Mopars with Big Daddy". Running between 73 & 80 with a couple of WOT runs to 100 or so AND stopping often for the dog, I got an honest 15.1 mpg (made it on one tank, too )

 

I think I can explain a little. What you have witnessed first hand is a change in the gasoline formulation for winter.
To help, limit acceleration----I know--well duh, Try to keep the engine RPM under 2000. The frictional loss (parasitic) increases dramatically above that...in other words, slow down or pay up at the pump

 

Yep, one thing has changed. We are now into "winter gas"...

 

Thanks, I'll work on keeping it below 2000 rpm's and see how that helps. I'm gonna miss that deep throaty exhaust note at 2500 and up. Did they really change to winter fuel this early? I knew to expect worse mileage around winter time, but I noticed it in early September and that's what was confusing me.

 

I noticed it too. I live just South of you and used to commute to Kzoo every day for work.

 

I was gonna say "read the plenum thread", but then I remembered...LOL!

 

All the advice given is good. I can verify that if you can manage to keep the tach under 2K at ALL times, it does improve the mileage significantly. Hard to do though... ;>)

A couple of other things I've experienced though that you might keep in mind. One is that I started noticing poor indicated fuel consumption and then I found the cruise control wouldn't work properly. The problem was the speed sensor on the top of the rear differential housing. It was covered in metal filings, which is typical with the limited slip clutch pack retaining clips coming undone and getting chewed up in the differential. Not always fatal and in many cases you can probably clean up the filings off the sensor and get it to work properly again.

Another odd thing that I noticed was fuel consumption was poor recently. I noticed that the idle was somewhat erratic with a bit of what seemed like a miss. I was thinking spark plug time again, but then the truck catastropically failed one day on my wife. Crusing along no problem, rolled off the gas as she approached slow moving farm traffic. When she got back into the gas to pass, nothing happened. Engine sped up... truck didn't. She pulled over and the truck would run, but wouldn't move.

I went and checked to ensure the rear end hadn't failed, but no driveshaft movement at all. The engine would start fine, but the idle speed was weird and wrong. I did a lot of troubleshooting the tranny and in the end had to replace the whole torque converter/transmission/cooler with a Jasper rebuilt system. Oddly, after doing so (no tune up or anything else was done) the idle was perfect again and mileage was back up to 18-19+ on the highway. I do have a rear tonneau cover and a Superchips tuner programmed for the 87 octane level. Truck is still scary quick at that tune when needed, but does get reasonable mileage, if you can keep your foot out of it!

Hopefully you don't have one of these other issues, but just to share with others as well. I wasn't expecting an automatic transmission to cause these other problems, but unless there is another unknown to me cause of the idle and fuel consumption, there does seem to be some connection.