Join Date: Jan 2014
Joe Cool is offline
Re: 2001 RWD still getting bad gas mileage
It cost me $30 to hand my new Ebay MagnaFlow cat to the exhaust shop, have them cut out the old one and weld the new one in. His only requirement was he kept the old cat. As someone who has made and installed a new Y pipe/cat assembly in my truck with out the right equipment, I highly recommend taking it to a shop.
As far as mileage goes, once you get the exhaust fixed, there should be an improvement. My '03 RCSB V6 5 speed is getting just over 19 mpg right now with 50/50 city/highway driving. It has dropped about 1 mpg in the last 2 years or so, but it does have 240K on it. I bought it new, and am meticulous about preventative maintenance (obsessive, probably spend too much), which I believe has helped in the long run. I do however drive it "enthusiastically". On the other hand, I will keep it in 5th gear during steady drives of 35 mph or higher. It has plenty of torque to drive at 1,500 or lower.
When you get the known issues figured out, the thing you need to remember is your new truck isn't the same as your old one. There are variances and tolerances that can effect the gauges, not to mention how the vehicle is treated throughout it's life. My first two cars were both Oldsmobile Cutlass Cieras, the first a 1986 and the second a 1989. When I bought the second one I couldn't figure out why it had a gas can in the trunk. The next day when it ran out of gas at 1/8 tank I realized why. Even my current truck's gas gauge will vary. Over the life of my truck when I fill the tank I can drive between 30-100 miles before the needle will move. The distance will change when ever I reset the the computer to clear a CEL.
In my opinion you need a larger sample size to determine your trucks gas mileage, maybe 4-5 fill ups at least. Something to consider when filling up is how consistently your truck will top off at the pump. When filling my '96 the pump would shut off and I would be 2 gallons short of full. Every time. My '03 when new was completely different and when the gas pump would shut off, it was full. Now with age, I have to hold the nozzle just right or it will shut off before full.
Basically, you're on the right path by fixing the known issues, just realize the results are not always clear. You may have to temper your expectations to circumstances a little.