ArcticDC5

Can't figure out what is going out or wrong with my 3rd gen. I used to get to half a tank around 170 miles and now I am lucky if it sees 150. It barely makes 200 miles at 1/4 of a tank left. I mean, I filled that thing up to the brim on Sunday and driving on the highway, I saw the needle go away from the F after about 14 miles, I was like WTF?! I shift between 2,000 - 2,500 RPMs

its a 91 5spd w/171k
the following parts have been replaced:
-fuel injectors (from a junkyard with a wrecked max that had 89k)
-use techron fuel system cleaner every 3k miles
-use 89 octane fuel
-air filter
-fuel filter
-knock sensor (but no harness)
-cleaned MAF with electronic parts cleaner
-air pressure on the tires is OK
-plug wires, distributor cap/rotor
-spark plugs

I'm clueless as to why I am getting sh*tty mileage

Greeny

iTrader: (43)

O2 sensor maybe

internetautomar

iTrader: (30)

Leaky exhaust, bad injectors, coolant temp sensor malfunction are all possibilities.

ArcticDC5

exhaust manifold studs are broke I know.

Coolant temp and O2 sensor have been replaced recently as well.

vansskaterfreek

iTrader: (14)

maybe that fuel system is messing up your injectors..... i heards it does that sometimes

internetautomar

iTrader: (30)

fix that exhaust leak.
once you do your mileage should go back up

decus

Hmm, just to state the obvious, but because it sounds like you are just measuring mileage via the fuel gauge, the sending unit might be shot and not giving a good reading anymore....overtime the **** in the fuel sometime makes the sensor go out of wack.

jwmaxse

iTrader: (1)

Yeah I think it's a good idea to start keeping track of your mileage by figuring it out when you fill up the tank instead of estimating it by watching the needle.

One big thing that can affect mileage is the winter. You get worse gas mileage for a number of reasons in the winter:

-Engine doesn't run as well in the extreme cold
-Alot of people warm up their cars in the winter
-Driving in snow can use more gas if you constantly rev the motor
-Some gas companies even use a different gas mixture in the winter I think

Something else to consider is that if you're only getting 20-30 miles less on a tank of gas then that only changes your gas mileage by 1-2 mpg's, so that's not a huge difference.

Jeff92se

iTrader: (82)

I went a good 45 miles and the guage didn't even move. Does that mean I'm getting infinite mileage?

bhunter

iTrader: (3)

How much difference should wider tires make? My red car seems to run just fine but my mileage has dropped 3-4 mpg on the highway.

internetautomar

iTrader: (30)

Rolling resistance + Heavier rotational mass = mileage drop

jwmaxse

iTrader: (1)

Funny, but that's pretty much the logic of some of these gas mileage issues. People need to stop trusting their fuel gauges and keep track of their mileage every time they fill up instead

ArcticDC5

Ok, so i filled up the tank tonight and it was basically on E with 294 miles on the trip odometer.

Filled 14.5 gallons of gas in the Max, and then I went into my briefcase and got out my calculator. 20.5 miles per gallon. Hmm, I used to average 25 mpg 2 months back. I somehow lost 4.5 mpg somehow. I popped the hood and looked for the fuel rail lines and the one that was visible on the passenger side was dry, couldn't see under the intake plenum for the other one.

I'm really clueless here.

internetautomar

iTrader: (30)

.

ArcticDC5

The exhaust is all new minus the pipe that goes in between the cat and the muffler. Otherwise I have a new cat, muffler, and y-pipe. I am sure there are a few exhaust studs broken, but once the car is warmed up, I don't hear the ticking noise when accelerating.

Bad exhaust manifold studs would really screw my mileage up like this??

jwmaxse

iTrader: (1)

I don't frequent this site very often for obvious reasons but read the article on this webpage and you'll find your answer:

http://www.wholesomebabyfood.com/frugal14Dec.htm

So did you fill up the car all the way or did you just put 14.5 gallons in? In order to keep as accurate gas mileage as possible you have to fill the tank up completely, set the trip odo. to "0" and then fill it up completely the next time and calculate it then.

Your gas mileage is most likely just being affected by the weather and the different gas mixture though, I just recently got 330 miles on my last tank, I normally get 370-380.

Oh yeah, the exhaust stud issue will give you less power and worse gas mileage if they are leaking badly enough.

internetautomar

iTrader: (30)

it can, because air is getting into the exhaust before the o2 takes its readings so it keeps reading lean and the computer tries to compensate by adding more fuel.