I have a 2001 GMC 1500 4.8l and I am getting 11-12 mpg's on the highway, could this be an 02 sensor? My air filter is new, plugs, wires, and fuel filter are also new.
GMC Q&AAsk Your Question
2001 GMC Sierra 2500 Question: O2 Sensor and poor MPG's
Answer #1DaveJHM January 03, 2011, 01:20Master
If you had an oxygen sensor causing that much of a fuel economy loss, your OBDII check engine light would come on based on a "lean" fuel trim issue.
A good diagnostic test is in order to see what is going on with your truck. A solid fuel economy test should be done. Make sure there is nothing causing an issue aerodynamically.
Replyalsaaron, January 03, 2011, 10:43Rookie
There is a check engine light on, I will shoot up to Autozone and have them check the code.
ReplyDaveJHM, January 03, 2011, 22:53Master
OK, yes, check the check engine light - and if you have P0171 and P0174 together, you have a vacuum leak, air intake leak or something like that...which will make the engine ask for more fuel.
Replyalsaaron, January 03, 2011, 23:07Rookie
I checked the code today, it said engine cylinder misfire...
ReplyDaveJHM, January 03, 2011, 23:33Master
This too can consume more fuel, if fuel is unburned by a misfiring cylinder.
Or, worse yet, you could have a fuel injector on the misfiring cylinder sticking open. Check your oil level - does it smell like fuel at all? Is it high at all?
These are just thoughts. A good diagnosis is in order, otherwise it will be lots of guesswork. Good luck.
Replyalsaaron, January 04, 2011, 00:29Rookie
Thanks Dave, I will have too look into it a bit deeper.