Gas Milage Went To Pot

[bigblockrocks]

I have a 2001 Chev 2500 HD Crew Cab Short box 4x4 with an 8.1 L /Allison Combo. I used to get 16mpg, Now I get 10mpg. Have flushed the fuel system, changed the fuel filter, plugs and wires and new air filter. Got a little more power back but the milage still sucks...Anyone have any ideas

[2000DV4.8]

I have a 2001 Chev 2500 HD Crew Cab Short box 4x4 with an 8.1 L /Allison Combo. I used to get 16mpg, Now I get 10mpg. Have flushed the fuel system, changed the fuel filter, plugs and wires and new air filter. Got a little more power back but the milage still sucks...Anyone have any ideas

 

 

16mpg with an 8.1? I find that hard to believe, I barely average that with my 4.8...

 

Any idiot lights on the dash?

 

Does the exhaust smell like rotten eggs? If it does, you got a bad cat.

 

Are you running the same tire pressure?

 

Running more aggressive tires?

 

For how many tanks has the bad gas mileage been going on?

[bigblockrocks]

I have a 2001 Chev 2500 HD Crew Cab Short box 4x4 with an 8.1 L /Allison Combo. I used to get 16mpg, Now I get 10mpg. Have flushed the fuel system, changed the fuel filter, plugs and wires and new air filter. Got a little more power back but the milage still sucks...Anyone have any ideas

 

 

16mpg with an 8.1? I find that hard to believe, I barely average that with my 4.8...

 

Any idiot lights on the dash?

 

Does the exhaust smell like rotten eggs? If it does, you got a bad cat.

 

Are you running the same tire pressure?

 

Running more aggressive tires?

 

For how many tanks has the bad gas mileage been going on?

 

 

Same tires and tire pressure...No goofy lights. Guess i,m talkin' in Canadian gallons. US would be about 16 not 18 and 9 not 10.

Problem has started in about the last 5000 miles or so.

[Hammer2785]

O2 sensors?

[silversport]

02 sensors or cats???

Bill

[jrrod2004]

If you had a disconnect of the battery, that could do it. If not, then disconnect your battery (batteries) and leave em disconnected at least 4 hours (my own personal recommendation), some will say that 30 mins is just fine, I usually go off the deep end on this type of stuff. Once you reconnect the battery (batteries), start it up and let it idle for 10 mins (IMHO) and then take it for a drive (errands, work, hunting, or whatever) and drive it for several days with different styles of driving (city, highway, slit your wrist traffic etc ). Gotta give the computer to 'relearn' everything.

[jrrod2004]

by the way, did you seafoam it???

[cargoone]

O2 sensors?

 

 

x2 on O2 sensors

 

or Clean MAF, dirty EGR or plugged convertor

[bigblockrocks]

O2 sensors?

 

 

x2 on O2 sensors

 

or Clean MAF, dirty EGR or plugged convertor

 

 

I tried to take the MAF out and clean it...Darn thing wont come out...is there a trick to it...Don't want to break it. Also my brother in law has a guage to check the back pressure...thats me next step.

Thanks for the advise guys.

[BDPatriot13]

16.2 around suburbs (0-40 MPH)