Finally got my car (89 240sx coupe) legal and been driving it around, and i noticed something...gas milage is terrible. After driving ONLY 38 miles, i'm down to HALF a tank (From a FULL tank). What could cause suck a HUGE impact on gas milage?

 

Could need a tune up. Could need an oxygen sensor. Could have a vaccum line leak. Could be a combination of alot of things.

Also could need a fuel cell replacement. That happened on my Pathfinder. Gas gauge was totally wrong.

 

WOOHOO
well sorta
Did a self diagnostic, and got a engine code 13
Coolant temp sensor
Not hard to replace..however..one problem, how do i replace it?
Any suggestions would be pretty cool

 

hmm, never replaced one of those before, so I can't help ya there.

I don't see how that would cause bad gas mileage though .

 

do your rpm's bounce?

if so it's the intake manifold gasket and intake plenum gasket.

500 USdollar repair.

 

Eh..idle is about 700 strong *sometimes* however it is sometimes also at 1500. My tranny (auto, bleh) is messed up and doesn't like shifting so it makes it hard to tell.

500 dollar job eh?
Doesn't sound hard to do it yourself :P

 

oh no you wouldn't want to do it yourself. i dropped the car off at 730 am and got it back at 215 pm when i was supposed to get it back at 430 pm. it was a master mechanic too... it takes a while and he was dedicated to my car.

it the rpm's don't bounce though it's not those two gaskets.
youi can single out the plugs and the wires so it has to be a sensor or a cracked rubber hose basically meaning a leak.


:edit: i imagine it's running extremely rich to have that bad milage. what does it smell like when you stand at the tail end of the car?

give us some more symptoms.

 

Cold, it's a nice rich gas smelling smoke, after awhile it goes away, still there tho (smell).
It drives super strong, doesn't miss a beat, does hesitate and feel like i'm drowning a cat in water at idle at times. Again, i dunno if my failing alternator is a reason for that.
Now, i wonder if it could be an exhaust leak (maybe headers?), because it is loud, i dunno if stock is suppost to be that deep.

 

so for sure it's HALF tank and not just the gas gauge? i know mine stays on full for about 250-300 miles, then drops sharply to a quarter tank or less

i mean 38 miles on half tank? if the tanks are about 15 gallons (i think the s14 is 17 gallons), you're getting about 5mpg. i think with all the problems mentioned above i would think you'd get maybe 10-15 mpg.

i'm making an educated guess on that one, but that sucks.

 

The gas gauge is indeed right. I have killed the tank at 120 miles per a full tank. The idle seems a little irractic too. I drove for about a constant 80 miles, and it didn't die, the car DOES idle at 700, wonderfully infact, just sometimes it doesn't and it hits at 1500 at operating temp. It was a little scary because it sometimes felt that the car was gonna die. But the gas gauge is correct.

 

Coolant temp sensor is located on the left side of the engine (when facing the car from the front). Follow the upper radiator hose to where it enters the block - on that section of the block you'll see 2 sensors with wires coming out of them that are inline with the flow of the coolant through the radiator hose. The coolant temp sensor is the one closest to the radiator hose.