I have tried the impossible to improve the gas mileage on my Classic beyond the 25-26 mpg limit.

I drive 70% freeway/30% surface streets. Speed is between 70-75 mph with the tach a hair above 3500 with the AC on.

I have done all that is required:
changed O2 sensor
change plugs, wires and rotor and cap
set timing at 15 and idle speed at 800 +/-50
Checked the CAT and it is fine.
Set the pulg gap to one mm
Cleaned the throttle body
regrounded the MAF

Is there anything left to do? I am at a loss as to why the gas mileage does not match the 28 mpg that I got on my 200SX when it was street legal.

Is it because the car has 138K miles? If anyone has tips on how to improve the mileage, then please share them. I hate it when I cannot find out the cause of a problem :mad:

Is your ecu throwing any codes?

Because of the Fuel sending unit problem I can only get 220 miles out of a tank when the needle hits E. But If I run it till I get the gas light to come on I easily get another 80-100 more miles.

Could this be your problem?

Try putting higher octane fuel if all you get is regular. When I first got my classic i ran on 87 for a few weeks and was only able to muster about 25 mpg. I switched to super (93) and got 29-31 MPG. This was about 30% highway driving at the time too.

Also, try tire pressures? Although, I'm sure you are on top of that.

Some Redline SL-1 fuel additive couldn't hurt either.

Strange... I was able to get about 35mpg in my NX in 95% highway/5% city driving... This is with the car in its current state, running 91 octane, with average speed of 85mph going from San Jose to LA. The car's mileage never got below 25mpg. Well... Except when on the track where the mileage never exceeded 15mpg.

you set ur plugs to 1mm??

Originally posted by Its311Pete
Because of the Fuel sending unit problem I can only get 220 miles out of a tank when the needle hits E. But If I run it till I get the gas light to come on I easily get another 80-100 more miles.

Could this be your problem?

The amount of fuel left in your tank when you fill up has nothing to do with gas mileage.

Chris

The amount of fuel left in your tank when you fill up has nothing to do with gas mileage.

True
I was thinking about getting Miles out of a tank of gas instead of MPG.:rolleyes:



Darren

Originally posted by mpg9999
Is your ecu throwing any codes?
There are NO codes at all.

Originally posted by NismoSER
Try putting higher octane fuel if all you get is regular. When I first got my classic i ran on 87 for a few weeks and was only able to muster about 25 mpg. I switched to super (93) and got 29-31 MPG. This was about 30% highway driving at the time too.

Also, try tire pressures? Although, I'm sure you are on top of that.

Some Redline SL-1 fuel additive couldn't hurt either.
I am going to try a tank or two of 91 octane gas. That is the highest we have in CA. I have been running 87 since I got the car. I have set tire pressure before, but I have not done it of late. I think I had them set at 32 all around. I am also running 205/50 wide tires on 15 inch 200SX rims. Could that cause a loss in gas mileage by 1-2 mpg?

I have some NOS octane boost. I might try it with a 91 octane gas tank and see what happens.

I have 205/50's on stock B14 wheels as well. With Fmax Stage II turbo kit(and S3 cams) I get no lower than 25mpg and average around 30/31mpg!! On long highway trips I consistently get 34mpg on the dot. I have repeatedly gotten this. (7psi and yes I romp on it all the time)

I can't say enough good things about the JWT Turbo program with regards to mileage. Simply outstanding.

Naji I think you may have an emission related device causing your less than average mpg.

P.S. With the JWT ECU - POP/NA Program, pre-turbo days, I got very similar numbers except on long trips. Long trips yielded more of a 32mpg average. One other thing, I have ALL emission devices on my car, with none of them disable/altered in any way, including the stock cat.

Cold Air Intake maybe. It is possible that the air entering the MAF at speed is the same temperature or less than cold idle. Therefore causing the ECU to dump more fuel into the motor? When I had the POP I had much better gas mileage. Just a thought.

I had Place Racing CAI when I was speaking above in regards to N/A form.

Well, I have a similar problem. I was getting 24 mpg city and up to 35 mpg hw as recently as a month ago. Now, I'm getting about 21 city and 27 hw. It's pretty sudden. No codes are being thrown by the ECU. I reset it to see what happens. I thought it may have been related to the water pump seizing before, therefore creating worse mileage. But that is fixed and the mileage hasn't increased all that much. So far I've been figuring that the car is readjusting. I guess I'll find out on the next fillup.

Originally posted by DaGenesis
you set ur plugs to 1mm??

whoa, hope thats a typo

I dont' even want to get in on the topic of gas mileage. When I used 87 octane and had 10* timing I thought it was bad for a 4 cylinder car........ Now with 18* and 93 octane it feels like my money is blowing out the exhaust as I drive:mad:

I got about 19mpg out of the last tank. (Last week) But this is me with barely any highway driving and a lead foot. I spend alot of $ on gas. :p

Originally posted by Chrissy
I got about 19mpg out of the last tank. (Last week) But this is me with barely any highway driving and a lead foot. I spend alot of $ on gas. :p

Im with Chrissy, when i drove my 92 everyday, i was getting like 16-18 MPG! :confused: It was all local driving. I did EVERYTHING, plugs wires, O2, cap and rotor. I dont remember the last time i got over 20MPG! oh well...

Originally posted by chriscar
The amount of fuel left in your tank when you fill up has nothing to do with gas mileage.

Chris

When I get gas, I divide the mileage on my trip meter by the amount of gas I put in. When my sister drove the Sentra, she complained that it only got a little over 200 miles on a tank. Once I got it, I noticed that even though the needle was touching E, I only put in 8 gallons. With the 200, at the same point, I put in 10 or 11 gallons.

my gas mileage usually spikes up after an oil change. i use mobil 1 and change every 3000-5000 miles. prior to an oil change, i usualy get ~25mpg. after i change the oil, i would get closer to 30 mpg. i drive 200/100 highway/city miles per tank. i drove 350 miles on the last tank - gas light went on around 330 mile. it was about 12.2 gallons to fill up. i'm sure most people get the oil change phenomenon, but yeah, i'd like to know other ways of upping gas mileage!