poor gas mileage?

[thecrash91]

i have no egr, and i keep reading how people get almost 30 or more mpg at highway, i have a 2002 p5 standard, my mods (performance related) are high flow cat, obx headers, magnaflow exhaust, injen CAI converted to SRI, but when i drive from my college (utica NY) to my girlfriends college (syracuse NY) which is only about 60 miles i use a quarter tank. so when i drive her back im on half so im getting about 20 miles to the gallon, i highly doubt my mods would do this, im runnin regular gas. what could be the problem? its been like this for a while and i dont think im runnin rich, i just changed spark plugs and coils cuz i was boggin something fierce, and now im bogging again i think its the wires this time though. could bad wires give me s*** gas mileage?

 

[slavrenz]

i have no egr, and i keep reading how people get almost 30 or more mpg at highway, i have a 2002 p5 standard, my mods (performance related) are high flow cat, obx headers, magnaflow exhaust, injen CAI converted to SRI, but when i drive from my college (utica NY) to my girlfriends college (syracuse NY) which is only about 60 miles i use a quarter tank. so when i drive her back im on half so im getting about 20 miles to the gallon, i highly doubt my mods would do this, im runnin regular gas. what could be the problem? its been like this for a while and i dont think im runnin rich, i just changed spark plugs and coils cuz i was boggin something fierce, and now im bogging again i think its the wires this time though. could bad wires give me s*** gas mileage?

Yes. Change them.

 

[thecrash91]

haha i just realized i didnt mean i dont have an egr, i meant cel. but thanks, is there anything else that could give me poor gas mileage?

 

[isbre]

Start with the wires. Also a dirty MAF, dirty injectors, low fuel pressure, air leak, defective brakes (like a seized e-brake), air filter and carbon buildup in the EGR affects milage.

Naturally, 30+mpg requires that the engine internals are undamaged and things like pistonrings and valves are sealed tight. A compression test might be an idea to check that out.

 

[flash75]

Are you basing you mpg on the fuel gauge readings? Your question implies you are. That is not a very accurate way to compute mpg.

 

[sube]

I get 25city 32highway based on a US gallon, little less in winter but not a lot.

Pat.

 

[thecrash91]

im calculating it based on how much i drive and how fast it goes down. its not dirty filter, i just cleaned it, ill start with the wires and work my way up to the more expensive things. i cleaned the egr valve a little while ago, but i lost the gasket and put it back on without only to find the gasket on the ground when i moved the car. would that give me bad gas mileage?

 

[isbre]

im calculating it based on how much i drive and how fast it goes down. its not dirty filter, i just cleaned it, ill start with the wires and work my way up to the more expensive things. i cleaned the egr valve a little while ago, but i lost the gasket and put it back on without only to find the gasket on the ground when i moved the car. would that give me bad gas mileage?

What kind of filter do you use? and how did you clean it?
Bacause if you use the stock filter and cleaned it with pressurised air blowing the other way to get the dirt out you can throw away that filter now.
If you cleaned it with oil some of that oil may escape into the tubes and mess with the MAF. (Cleaning you MAF is also a cheap fix as long as you're careful.)

No EGR gasket may give you an air leak, don't know how much that one affects things though.

 

[flash75]

{im calculating it based on how much i drive and how fast it goes down.}

In other words you haven't determined what your fuel mpg is by calculating mpg= miles driven/divided by gallons of fuel consumed. If you do a correct fuel consumption/mpg calculation you may find your true mpg may be better than you think, it may also be worse than you think.

Clifton

 

[thecrash91]

well judging that driving 60 miles takes it down a quarter tank, and that we have 14 gallon tanks it actually came out to 17mpg. i have k and n filter on a sri, but the sri is converted from a cai. i didnt relocate maf though, could that do it since the maf is right behind the filter?
and no matter how much gas i have, full or half tank it always goes down a quarter tank every time i drive to my girlfriends college which is were im getting the 60 miles from.
p.s. im also driving 80mph when i go, so does having the rpm at 3.5-3.75k give me 17mpg?

 

[probin94]

well judging that driving 60 miles takes it down a quarter tank, and that we have 14 gallon tanks it actually came out to 17mpg. i have k and n filter on a sri, but the sri is converted from a cai. i didnt relocate maf though, could that do it since the maf is right behind the filter?
and no matter how much gas i have, full or half tank it always goes down a quarter tank every time i drive to my girlfriends college which is were im getting the 60 miles from.
p.s. im also driving 80mph when i go, so does having the rpm at 3.5-3.75k give me 17mpg?

yes...ive noticed that anything higher than 70 mph for an extended period of times kills the gas mileage. that high of an rpm range is a gas killer for sure in these cars

 

[cbrcrx]

You can't calculate your mpg on 1/4 of a tank. I had a car once that went as far on the first quarter as it did on the other 3/4ths.

 

[thecrash91]

well like i said no matter if its full or half or any other point on the gauge it always goes down a quarter

 

[isbre]

well like i said no matter if its full or half or any other point on the gauge it always goes down a quarter

I see your point, but just take the hint.
Fill the tank up to the point where you can see the gas, drive around, then repeat and calculate exact mpg. It will give you an accurate reference point now to compare it to when you have figured out what gives you poor gas milage. - And it will keep this thread focused on ideas that might help you instead of just talking about how you don't really know your mpg number with decimals. Approximate average speed and type of driving while measuring will also give a good reference point if your numbers are far worse than other P5's out there.

Did you try to clean your MAF sensor?