More Questions About Poor Fuel Milage In My 02 5.3

[niko11]

my 02 5.3 4x4 with 3:73 gears used to get 15 city/17 highway when it was new.i have a k+n air filter and a tornado which i had then as well. I had dual cat back exhaust on it at the time but i have since removed it. I now have been consistantly been getting about 11.5 mpg at about 50/50 city/highway here in maine. It is cold and i know that drops my mpg some. In 05 i let the truck sit alot and drove my car. I think i put like 2500 miles on it that year...mostly plowing. i took the dual off after that and started driving it full time again in 06. Since then i am getting horrible milage. I have 41000 miles on it and have recently changed to synthetic engine oil, changed the fuel filter, cleaned the k+n, adjusted the air pressure in my tires, ran injector cleaner and installed a hyper tech programmer. I just filled up and i am getting 13.1 mpg. That aint verry good. I need help. I know there is a lot of talk abot o2 sensors but i hate to dump $160.00 into it to find out that my o2's were fine. I have never had an ses light come on and was wondering if a scan tool could tell me if things were working right sensor wise. any input would be greatly appreciated!!!!

[z85violator]

if you could find the specs for resistance(ohms)per sensor, and then check your o2 sensors to see if they are within spec? i don't know the specs.

[pwall]

My truck's gas mileage has been not as good as it usually is. Just this week I had new plugs and wires installed, and two of the plugs on the drivers side were bad. I haven't been thru a tank of gas yet, but so far it appears to be much better. I'll know more over the weekend.

Anyways, may be worth the time to pull each plug and have a look. That doesn't cost anything but some time.

[RLGDiesel]

Most states now require gasoline to contain 10% ethanol. The lower energy content of this "gasohol" produces a drop of about 2 mpgs.

[pwall]

Not in Ontario. ;)

[niko11]

My truck's gas mileage has been not as good as it usually is. Just this week I had new plugs and wires installed, and two of the plugs on the drivers side were bad. I haven't been thru a tank of gas yet, but so far it appears to be much better. I'll know more over the weekend.

Anyways, may be worth the time to pull each plug and have a look. That doesn't cost anything but some time.

 

 

How many miles on your rig, and did you notice any hesitation problems etc.?? I would be interested to see if that helps you. I have yet to check my plugs because i have not had any hesitation issues etc. and they "say" these plugs are supposed to be good for 100k.

[Starrman]

How many miles on your rig, and did you notice any hesitation problems etc.?? I would be interested to see if that helps you. I have yet to check my plugs because i have not had any hesitation issues etc. and they "say" these plugs are supposed to be good for 100k.

 

 

The plugs on these 5.3l motors are easy enough to get to that it won't hurt to check them or even change them. I don't believe in these "100k mile plugs". Plugs are cheap, and I change mine on my vehicles about once a year on the daily drivers and even more often on my performance/race cars

[billo52]

Is the truck getting up to operating temperature? Don't just check the temp gage, measure the return hose temp with an infra-red or a contact thermocouple. You may have a stuck OPEN thermostat and the computer still thinks that it needs to warm up(very rich). or you may have a bad temp sensor(not the one that runs the gage). Just my 2 cents.

[niko11]

Is the truck getting up to operating temperature? Don't just check the temp gage, measure the return hose temp with an infra-red or a contact thermocouple. You may have a stuck OPEN thermostat and the computer still thinks that it needs to warm up(very rich). or you may have a bad temp sensor(not the one that runs the gage). Just my 2 cents.

 

 

do '02's have two temp sensors. I was thinking that there was only one. and for the thermostat being stuck open, wouldn't it be hard to warm the cab up??

[Westlotorn]

my 02 5.3 4x4 with 3:73 gears used to get 15 city/17 highway when it was new.i have a k+n air filter and a tornado which i had then as well. I had dual cat back exhaust on it at the time but i have since removed it. I now have been consistantly been getting about 11.5 mpg at about 50/50 city/highway here in maine. It is cold and i know that drops my mpg some. In 05 i let the truck sit alot and drove my car. I think i put like 2500 miles on it that year...mostly plowing. i took the dual off after that and started driving it full time again in 06. Since then i am getting horrible milage. I have 41000 miles on it and have recently changed to synthetic engine oil, changed the fuel filter, cleaned the k+n, adjusted the air pressure in my tires, ran injector cleaner and installed a hyper tech programmer. I just filled up and i am getting 13.1 mpg. That aint verry good. I need help. I know there is a lot of talk abot o2 sensors but i hate to dump $160.00 into it to find out that my o2's were fine. I have never had an ses light come on and was wondering if a scan tool could tell me if things were working right sensor wise. any input would be greatly appreciated!!!!

Have you changed the fuel filter? Should be done every 10,000 miles. Helps a lot if pressure is where it should be. Usually does not set off Check engine light if you lose a few pounds of pressure in the fuel system but it will affect fuel atomization, power and mileage. Good Luck, cheap replacement and needs done regardless of fixing your issue.

[Rammer]

Try cleaning the MAF sensor with a spray can of electronics cleaner. Oil from the K&N filter might be transferring to the sensor causing incorrect airflow measurement.

[Z71SIERRA]

I had plugged cats on my 2002 Z71 recently and I suffered a slow progressive decrease in gas mileage leading up to the point where I lost top end power. Looking back I had noticed a loss of passing power and some spark knock under hard acceleration in the several months leading up to when the power would cut out when accelerating hard. I never got a error code from the computer until the cats were nearly competely plugged. Since I had the cats replaced the truck runs like new and I have no spark knock, it runs strong and I got my gas mileage back. I still have the stock O2 sensors and plugs and wires. The dealer covered the cost of the cats since they are emission related. Also if you clean your mass air sensor use the new CRC mass air sensor cleaner. I know RAMMER above suggested electronic cleaner and that used to be the only thing that could be used but now CRC make a cleaner specifically for MAFs and it works great. I had a dirty MAF on my wifes Ponitac Montana and I couldn't believe the difference it made. Good Luck

[niko11]

I had plugged cats on my 2002 Z71 recently and I suffered a slow progressive decrease in gas mileage leading up to the point where I lost top end power. Looking back I had noticed a loss of passing power and some spark knock under hard acceleration in the several months leading up to when the power would cut out when accelerating hard. I never got a error code from the computer until the cats were nearly competely plugged. Since I had the cats replaced the truck runs like new and I have no spark knock, it runs strong and I got my gas mileage back. I still have the stock O2 sensors and plugs and wires. The dealer covered the cost of the cats since they are emission related. Also if you clean your mass air sensor use the new CRC mass air sensor cleaner. I know RAMMER above suggested electronic cleaner and that used to be the only thing that could be used but now CRC make a cleaner specifically for MAFs and it works great. I had a dirty MAF on my wifes Ponitac Montana and I couldn't believe the difference it made. Good Luck

 

Thanks for the input. That is one of the things that i wondering about. How did you find out that they were plugged, and what exactly plugs them up. Are they warrented past the 3/36

[redvett]

Cat's are warranted 8years or 80000mi.

[niko11]

Cat's are warranted 8years or 80000mi.

 

Thanks redvet, i'll have to call the dealership and schedule an appointment to have them checked out. Any one else had trouble with the cats on these trucks???