mileage -- 17mpg now down to 14 mpg

[T_love]

OK, last week was the first time i was able to calculate my mileage. it was 17mpg. That kinda shocked me but i figured its the first time so there may be other factors. Today i did it again and it was 14mpg. That's ridiculous. I'd have better mileage if i was driving a SUV.

I have a idling problem, my car idles at about 1500 - 2000 rpms when i start it after it has been sitting for a while( cooled down completely). It stays there for as long as it takes me to get wherever i'm going which sometimes is up to 45 minutes with some highway driving. Sometimes after driving for a while, if i stop somewhere then come back and restart it before it completely cools down, it idles around 700-900 rpms. When washing the car a couple of days ago i also noticed that the exhaust is black on the inside from the exhaust fumes, I'm talking about a nice layer of the black stuff when i ran my finger into the exhaust.(its not oil though). From the few threads i found on the Skyline boards, i think i'm running very rich (black smoke, crappy mileage). I'm going to try and change my O2 sensor and maybe even sparkplugs but i would like to know what might cause this coz even if i change all that it probably will come back in a week or so.

Gas is too expensive to waste like this, especially since i'm not even boosting at all. I have only seen the positive side of 3000rpms a couple of times.

Any ideas as to a possible cause or things i might want to clean, change(hopefully not expensive), diagnose,etc

[JonPowell]

Are you ready?

Coolant temp sensor, TPS, MAF, O2, wiring, spark plugs, coils, CAS, injectors, fuel pressure regulator. IAC, FICD, air regulator,

All of these things will make you car run ****ty/rich/screw with idle

[T_love]

Damn, i wish it wasn't snowing. I would have run out and tried to go down that list and eliminate a few things

What's/Where's the Fast Idle Control(?) Device? did i get that right?

Wiring, i hope, should be OK coz i was idling perfectly fine for a week or so.02 sensor is probably dirty and maybe reading off cause of the dirt from the black exhaust dusting/smoke (its not actually smoking from what i can tell). I think same goes for spark plugs.

[BoostFab]

the O2 sensor is the first thing usually cause bad gas mileage. do you have the fuel pressure regulator installed? high fuel pressure at can cause your car to run too rich and gas milage can be horrible.

i consistently put out over 300 miles on each tank. i don't drive like a granny either.

[T_love]

I have not installed the walbro pump yet and i still have the stock FPR. I had no nipple on my intercooler piping so i T-ed the boost controller off of the FPR. I don't know if that could be one of the factors. i'm going to try and get a new O2 sensor as soon as possible. Does it have to be a specific kinda or are they generally universal?

[Joe]

i hate to be so blunt but honestly what did you expect? its a turbocharged 6 cylinder with no emissions requirments.

i get 14.5 with my mines ecu with regular spirited driving.

the idle isnt going to affect your gas mileage that much, its a seperate issue that needs to be taken care of tho.

[JonPowell]

the O2 sensor is the first thing usually cause bad gas mileage. do you have the fuel pressure regulator installed? high fuel pressure at can cause your car to run too rich and gas milage can be horrible.QUOTE]

Remember the high idle

What's/Where's the Fast Idle Control(?) Device? did i get that right?

Wiring, i hope, should be OK coz i was idling perfectly fine for a week or so.02 sensor is probably dirty and maybe reading off cause of the dirt from the black exhaust dusting/smoke (its not actually smoking from what i can tell). I think same goes for spark plugs.

FICD is piggy back on the IAC...brown plug & purple plugs on the back of the intake mani...for the most part the FICD should not engage unless you have the rr defroster or the AX on

wiring, something can always vibrate loose/abrade

I have not installed the walbro pump yet and i still have the stock FPR. I had no nipple on my intercooler piping so i T-ed the boost controller off of the FPR. I don't know if that could be one of the factors. i'm going to try and get a new O2 sensor as soon as possible. Does it have to be a specific kinda or are they generally universal?

Stop being a dumbass and install that pump! When your engine blows from lower octane and less pressure you will kick yourself in the *** and get no sympathy from any of us. I can't believe you had time to install the boost controller, but not the pump or regulator. You are a disaster waiting to happen.

the idle isnt going to affect your gas mileage that much, its a seperate issue that needs to be taken care of tho.

I disagree, I think the idle is one of his biggest problems in his milage issue.

[T_love]

Sorry for the misunderstanding, the boost controller is the boost cut solenoid. I don't have any boost controller on. I'll get the fuel pump on. I'll also go through the wiring and see if anything got loose or broke off.

Kamin: I have yet to hear of anybody with mileage less than 20 mpg, that's why i'm worried. Also the fact that its going down. I honestly have not pushed the car at all. I've been driving like an old lady since the day i started the car so its almost like my car is NA right now(sort of)

[Joe]

Jon the idle is probably an underlying SIGN of a problem that is causing bad mileage. that ill agree with. but not just a high idle causing bad mileage.

and Tlove, Im pretty sure 20ish is the norm for mileage. if you are getting bad mileage WITHOUT beating on the car then something is probably up. just cruising there should be a big increase in mileage. the big long list that Jon posted should be gone over with a fine toothed comb.

[T_love]

I should be able to get sometime to go over the list at the beginning of next week. I'll let you guys know what i find out.

Does anybody happen to know what size wrench you need for the O2 sensor, the biggest i have(19mm) doesn't fit, neither does the 3/4 inch one

[JonPowell]

ALL o2 sensors are the same size...its the only universal thing in cars....

Go to the parts place & ask for an O2 wrench...

[T_love]

thanks Jon, will do.