Mud_Slinger

I have a 99 4.8l 4x4

Things I have replaced:

all plugs and wires
oil and filter
fuel filter
egr valve
maf censer
o2 censor
air filter

So here is my issue. I am getting really ****ty fuel economy. I know this truck is not going to get the best but I am only getting around 10 city and 11 highway IN 2WD!! This thing is not a 6.0. I could expect bad fuel economy if it were a fig v8. Now I was getting around 12 city a few weeks ago and I changed my maf and added a new k@n air filter and since have gotten worse economy than I had before. I am not pulling any codes at all either. So I really don't know where to go with this. I have slightly bigger tires than the truck calls for and a flow master single outlet exhaust. I don't think these little things are going to hurt much if anything.

CAN SOMEONE PLEASE HELP ME?

I am on the verge of selling this damn thing if I can not get the economy better. Bad thing is it runs awesome, better than it did when I bought it a year ago, better than it has the entire time I have owned it. Any help would be awesome.

6LCHEVYZ71

Could be the winter grade fuel.. Or your foot? Drop in K&N filter? or cold air intake?
You should be getting better than 11 HWY if you're not dawgin it. I get better than that & I have a 6.0L with 305/75R16s, same year model as you. Try filling up with 93 octane next fill up (after your needle is on E) and then see what your mileage is. Keep all other variables the same. Post back with results.

gotstylez

if its a k&n cold air intake... it could be that..on every truck my friends have had and mine that has had a cold air intake on it..all they do is bog it down and you get less power from it..

6LCHEVYZ71

That's probably because they're really hot air intakes unless you have separated the hot engine air from the filter. Unless the filter is REALLY getting cool air (not under the hood air), you are doing more harm than good. They look cool though

gotstylez

agree..LOL

mss

Try a tune ...... maybe there is something wrong with the ECM.

Mud_Slinger

The filter is a stock replacement filter

I took it to my buddies shop and had him hook his computer up to it again and it is saying the back 1 censor 1 and bank 2 censor 1 o2's are bad. It was not showing up at the point it was tested but showed they were not working properly since the last time my computer was reset which was about a week ago when I replaced my maf. So its hard to tell how often they really work right. I suppose that could be one reason its getting poor fuel economy. What do you guys think?


BTW, cold air intakes do look pretty cool, I just can't afford one

6LCHEVYZ71

yes that will definitely cause bad fuel economy; bank 1 sensor 1 & bank 2 sensor 1 are before the catalytic converter IIRC. Change both those O2s out. You're good on the drop in K&N filter.

Mud_Slinger

Can they only work improperly once in a while or will they work improperly all the time? I know when he run the scan they were working. I priced them and they are 69.00 a piece. So I guess I will have to drive my car a little more for a month or so. I will keep this updated as I get money to fix things. Thanks for all the help so far.

6LCHEVYZ71

To answer your question in short, they can work improperly sometimes. Sort of. It's just a sensor that helps determine how to trim the engine, more rich or more lean (more gas or less), based on the air-fuel ratio it 'senses' in the exhaust pipe. If it 'senses' faulty, because they're full of carbon deposits then it can give the computer a faulty reading, but the reading may still be within the manufacturers tolerances of working 'properly' thus not throwing a code but still causing less than perfect gas mileage.. I hope that makes a little sense for a laymans term answer.

When you start doing the math, it pays off in the end to have properly functioning 02 sensors. Think about it. 11mpg vs say.. 17mpg. Gas at $3 a gallon. 20 gallon tank. 6x20 = 120 miles you wasted on that tank (17mpg-11mpg = 6 times 20 gallons). That equates to $11.54 per tank wasted due to bad 02 sensors. 13 fill ups and you've already bought BOTH of them.