93 3.4 maro gets 15 mpg no matter what-why?

[no_doz]

i recently got a 93 camaro 3.4l v6 sfi with 4 speed trans & the engine & trans are controlled separately (which is nice!!) and ive been testing the gas mileage because the gauge doesnt work and no matter how i drive it-it gets an average of 13-16 mpg, this is on highway or in city, weather i baby it or i run it like its stolen-same gas mileage. im thinking a leak & am going to test it as such soon, what do you guys think? this car runs GREAT but idle sounds a little strange, has had most of a tune up except for plugs & wires-i havent checked the plugs but i intend to. also the fluids are fresh & they look fine (no oil & antifreeze mix or anything )-this car has 62.5k original miles on it!! and ideas as to why it would be getting gas mileage like this? i mean, its a fun car to drive, and 15mpg in town isnt awful especially if im running it hard (and i do), so considering i get to have my fun and -at this point- it isnt hurting my mileage, im not discouraged enough to park it :P. id like to get this thing to where i can get 30 hwy or near that, i know my luminas all used to & they weighed a little more, so i figure its capable of it-so why is it so low & unchanging if its not a leak?

[Dave_A]

Something is obviously wrong...

The V8 cars get MPG in the low 20s...

[no_doz]

oh i know-im thinking it has to be a leak because it runs great-no cel

[Dave_A]

Leak as in fuel leak?

Easy way to figure that out is get a fuel pressure test kit - if you have a fuel leak you will have a loss of pressure...

Should be < 40PSI

You can loan out a FP test set from AutoZone.

[no_doz]

if its not a leak-anyone have any ideas as to what it could be? with the exception of a slightly rough idle this engine runs GREAT

[IsaacHayes]

Reason, it's a gen1 iron head v6... LOL

Swap to aluminum heads would help not only in power, but mileage/efficiency as well..

Your O2 sensors may be old and shot too, that will effect mileage (and power).

[Dave_A]

if its not a leak-anyone have any ideas as to what it could be? with the exception of a slightly rough idle this engine runs GREAT

1) Bad sensor somewhere (is SES on)?

2) Loss of compression in one or more cylinders (Minor head gasket failure)?

3) Valves way out of adjustment

You should get high 20s-low 30s for MPG with NORMAL driving, and less if you drive it like you stole it...

[60dgrzbelow0]

Location of the Schrader Valve on a 93-94 3.4L Eng

Leak as in fuel leak?

Easy way to figure that out is get a fuel pressure test kit - if you have a fuel leak you will have a loss of pressure...

Should be < 40PSI

You can loan out a FP test set from AutoZone.

These images show where the Schrader Valve is located for you to attach the Fuel Pressure Gauge. When you are finished testing for FP, turn off the engine and have a clean rag handy when you later remove the hose and adapter so fuel won't spray in your face or on the hot engine when you gradually unscrew the hose from the fuel rail.

Is there any chance that someone put in either after-market fuel injectors or the wrong (over-sized) ones? The Stock GM Multec EFI is marked with P/N 17103007 and is rated at 18 PPH. If larger ones are installed, they will not only cause poor gas mileage...but in addition, the excess fuel can sort of "water down" your engine oil by thinning out the oil left on the cylinder walls during the cycling of the pistons and then migrate back into the oil pan. Once there... the gas in the oil will reduce the lubricity of any kind of oil you have in the pan and bad things will be happening sooner than later. You can pull the dipstick and move away from the car a good distance before you gingerly smell the oil for the presence of a heavy gasoline smell and this might indicate that someone before you installed the wrong sized fuel injectors in the engine. The rough idling is also a symptom of "big" injectors trying to put more fuel in the motor than the stock PCM can handle while trying to mix it with air. The same problem of "Gassy Oil" occurs with badly worn rings.

[no_doz]

how do i check the injector rating?

[Iyyob]

i have a 95 3.4 and i get about 30 MPG ...

[mongo]

Mileage isn't all about the engine. How is your Transmission?

[no_doz]

not great-when in anything but D if i run it hard it wont shift unless i let off a bit (yes i do realize you should always do this for the sake of the transmission, but running it hard will usually point out problems that would otherwise stay hidden. i also have noticed a small amount of tranny fluid leaking near where the engine/trans mate up. if this is the reason for my poor mileage then i am definitely swapping to 5 speed.