Cause For Concern?

Whocares05050 · November 18, 2009

Info:

2004

GMC Sierra SLE

Extended cab 5.3

MODS:

K&N Performance intake

Maganflow Muffler

Issue::

recently i wanted to improve my trucks fuel mileage and driveability. I changed the intake, changed the plugs and wires, had my shop perform the GM Fuel induction service, and have been running 93 octane for 4 months now. About 4 -5 days ago, i changed my primary o2 sensors just incase they were getting "lazy". My trip indicated me improving my gas mileage from 15.8 to 18.3. Nothing changed, driving conditions and distance remained the same. Just yesterday my idle started to get a little rough. Not a misfire rough, more like too much fuel rough. And my mileage has decreased steadily as im driving i can see it lower from 18.3 to now 15.4. I have no CEL and no codes from the scanner. The truck was topped off to a full tank and now at the half way mark its starting to do this.

Could the cold front i had in florida cause moisture to build up in the tank? Could it be bad gas? I need some suggestions on what it could be.

Truck has 75,230 miles on it.

Thanks for all the help. Ive tried searching and came up short.

[email protected] · November 18, 2009

fill tank with regular 87 unleaded,sounds like you got a tank of 'heavy ' fuel.super unleaded has additivs in the fuel that can cause it to vaporize to slow mainly if the fuel has set around to long.

csheatz · November 18, 2009

sounds like a gas problem, try some dry-gas to get you through this tank.

Whocares05050 · November 18, 2009

fill tank with regular 87 unleaded,sounds like you got a tank of 'heavy ' fuel.super unleaded has additivs in the fuel that can cause it to vaporize to slow mainly if the fuel has set around to long.

Everytime ive switched back to 87 the truck always seem to run like shit. Ive never had an issue with 93 up until now ( thats if it is the fuel in the first place.)

Since ive got a half tank of 93 in there, think i should top off with 87 to level things out?

compulynx · November 18, 2009

One other thing to think about. E10.

When I pump E10 when visiting Fla (seems that is all they have) my mileage goes down a few mpg.

Did you have regular gas the first tank, then get hold of some E10? That would explain it.

I am still baffled as the what these "green" folks are thinking when they replace 10% of the gas with corn droppings, then you get 10% worse mileage. After you figure the polution caused making the E10 additive, you probably actually have MORE polution.

No common sense left in the USA today....

C

Whocares05050 · November 18, 2009

ALL fuel in florida has 10% Ethonal by law now. i live in florida and use the same gas station every time.

jblakeney · November 18, 2009

ALL fuel in florida has 10% Ethonal by law now. i live in florida and use the same gas station every time.

Engines will get addicted to a certain octane level. If you have always had 93 in it keep it up. It is a good possibility that 87 could make it run like crap. 10% ethonal is bs..... it drops fuel mileage........ In my area a bunch of the stations have the ethanol enriched fuel. I drive right by and swing in the shell stations that HAVE nitrogen signs (they are the ones that also say NO ETHANOL). I get 15-16 with a 75/25 interstate/city blend of driving.

Also, changing sensors, plugs, and wires could this have been the culprit that gave you the 18mpg, as the computer recalculated the increase in fuel mileage.

Jbo

dlstewart01 · November 18, 2009

http://www.wanderings.net/notebook/Main/Is...asWorthTheMoney

http://www.carlocate.com/Articles/High-Oct...ticle.aspx?id_7

Spurshot · November 18, 2009

One other thing to think about. E10.

When I pump E10 when visiting Fla (seems that is all they have) my mileage goes down a few mpg.

Did you have regular gas the first tank, then get hold of some E10? That would explain it.

I am still baffled as the what these "green" folks are thinking when they replace 10% of the gas with corn droppings, then you get 10% worse mileage. After you figure the polution caused making the E10 additive, you probably actually have MORE polution.

No common sense left in the USA today....

C

Actually, my understanding of E10 was that it had more to do with economy than ecology. No, not your truck's fuel economy, the farming industry's economy. It drove the price of other crops up and increased demand of corn. It's been a big boon to the farm industry. It f#*ked the rest of us over, but what the hey...or hay.

I'm a believer in the lowest octane that works crowd. There is more BTUs per gallon in most lower octane fuels than higher octane fuels.

Whocares05050 · November 18, 2009

One other thing to think about. E10.

When I pump E10 when visiting Fla (seems that is all they have) my mileage goes down a few mpg.

Did you have regular gas the first tank, then get hold of some E10? That would explain it.

I am still baffled as the what these "green" folks are thinking when they replace 10% of the gas with corn droppings, then you get 10% worse mileage. After you figure the polution caused making the E10 additive, you probably actually have MORE polution.

No common sense left in the USA today....

C

Actually, my understanding of E10 was that it had more to do with economy than ecology. No, not your truck's fuel economy, the farming industry's economy. It drove the price of other crops up and increased demand of corn. It's been a big boon to the farm industry. It f#*ked the rest of us over, but what the hey...or hay.

I'm a believer in the lowest octane that works crowd. There is more BTUs per gallon in most lower octane fuels than higher octane fuels.

Ok... Some new information as of today. I ditched the topical snanner for a snap-on scanner. Still no codes or pending codes so we dug a little deeper. While the truck was idling we notcied no immediate issue. We then proceeded to put the vehicle in drive with the brake in place, then immediate back into park. The scanner picked up a slight mis-fire in cylinders 1, 3, and 7. No enough of a misfire to throw a code, just enough of it to notice a choppy idle.

Im going to change out my wires in case this is the issue. They are brand new bosch wires, but when i installed them a couple weeks back i had an issue with them not wanting to fully stay on the coil. So im thinking there not making a good connection. Im changing them out with some napa ones that look a hell of a lot better and see if that was my issue.

Im also going to slowly bring the octane rating down as i fill it up. I had a half tank of 93 in there and just put 4 gallons of 87 in bringing me to 3/4 of a tank. so ill slowly bring it back down so its not a rough on the truck so hopefully itll learn the differant fuel trims and octane. Hopefully ill have this completed and updated by saturday. Regardless, im still taking suggestions.

Thanks again for all the help.

dlstewart01 · November 18, 2009

I'm a believer in the lowest octane that works crowd. There is more BTUs per gallon in most lower octane fuels than higher octane fuels.

Actually thats true, 87 has more BTUs than 93

Silverado4x4 · November 18, 2009

You might try cleaning your MAF sensor also as it may have got the oil crud on it from the oil on the K&N filter.

Whocares05050 · November 19, 2009

You might try cleaning your MAF sensor also as it may have got the oil crud on it from the oil on the K&N filter.

AH, very good. Havnt even thought of that. Its been almost a month since i installed it, and orginally cleaned it, but have totally forgot about it. Ill add that to my agenda friday when i change out the wires. Thanks.

jblakeney · November 19, 2009

One other thing to think about. E10.

When I pump E10 when visiting Fla (seems that is all they have) my mileage goes down a few mpg.

Did you have regular gas the first tank, then get hold of some E10? That would explain it.

I am still baffled as the what these "green" folks are thinking when they replace 10% of the gas with corn droppings, then you get 10% worse mileage. After you figure the polution caused making the E10 additive, you probably actually have MORE polution.

No common sense left in the USA today....

C

Actually, my understanding of E10 was that it had more to do with economy than ecology. No, not your truck's fuel economy, the farming industry's economy. It drove the price of other crops up and increased demand of corn. It's been a big boon to the farm industry. It f#*ked the rest of us over, but what the hey...or hay.

I'm a believer in the lowest octane that works crowd. There is more BTUs per gallon in most lower octane fuels than higher octane fuels.

Ok... Some new information as of today. I ditched the topical snanner for a snap-on scanner. Still no codes or pending codes so we dug a little deeper. While the truck was idling we notcied no immediate issue. We then proceeded to put the vehicle in drive with the brake in place, then immediate back into park. The scanner picked up a slight mis-fire in cylinders 1, 3, and 7. No enough of a misfire to throw a code, just enough of it to notice a choppy idle.

Im going to change out my wires in case this is the issue. They are brand new bosch wires, but when i installed them a couple weeks back i had an issue with them not wanting to fully stay on the coil. So im thinking there not making a good connection. Im changing them out with some napa ones that look a hell of a lot better and see if that was my issue.

Im also going to slowly bring the octane rating down as i fill it up. I had a half tank of 93 in there and just put 4 gallons of 87 in bringing me to 3/4 of a tank. so ill slowly bring it back down so its not a rough on the truck so hopefully itll learn the differant fuel trims and octane. Hopefully ill have this completed and updated by saturday. Regardless, im still taking suggestions.

Thanks again for all the help.

I heard you say something about a new intake???? Either way get out the WD-40 and spray around the intake gasket. You might possibly have a leak. If you get to a spot where you can spray WD-40 and it speed the engine or smooth it out.... That spot is a leak... ( could be you miss fires also the 1,3,5,7 is on one side... left side )

With that said 93 is usually pumped at a slower rate their for more susceptible to contain larger amounts of water. Also, if you get gas near the same time the gas station has gas delivered you are more susceptiable to geting a higher concentration of water. You might try some ISO-HEET its quite cheep. Pick up a bottle and drive home park wait an hour. Go back outside pour the contents in the tank and replace the cap. Wait 3 to 4 hours after pouring the contents in to drive the truck.

Jbo