Thread: Bad gas mileage? Why!?

Hey guys. So, I have a turbo p11. The motor is a w10 and I've been driving it for about 3months now. I know turbo motors are gas suckers, but for some reason my gas mileage is getting worst and worst. Here are my mods: gtir t28 setup(came with motor), jwt ecu tuned for the motor,z32 maf, and 4 bar fuel pressure, also nismo fpr and z32 fuel filter. Fuel pressure is set at 58psi with vacuum off. Timing is dead on 15*. I know turbo eats more gas, but please read on and you will see what I'm talking about.

The first week of driving the car, I noticed I was getting about 350 miles to a tank. That was driving only 5 miles per day in the city to work and back and did not smash on it since I was breaking in the clutch. I did that for a whole month to make sure everything was good to go. Now, I'm litterally getting 198 miles right when it hits at quater tank. That tank took 12.8 gallons to make the gas pump stop so I figured thats about 15.5 miles per gallon. I didin't pass 4k rpm at all with that tank of gas to see if its a problem with my foot to hear the bov or the exciment of turbo.LOL.. 3 weeks ago I did a road trip. Mostly highway driving, and logged 363 miles right on quater tank. So I know my highway mileage is about right.

Just last week, I did a oil change, spark plugs(gapped at .35), new z32 fuel filter, cleaned my K&N filter(pop charger btw), and filled my tank up which took 13.2 gallons. Now I'm already at half tank with only 74 miles. That's just driving 5 miles per day in the city, barely stop and go, also did a little highway driving to Walmart which is about 4miles of highway. I do have a wideband and when crusing it flacuates between 14.5 to 15.7. I know jwt run rich, but another crazy thing is, I did smash on it max boost set at 14psi and sometimes it goes as rich at 11.1 and sometimes it only goes to 12.4. I have a safc2, but did not touch the settings at all.

I do believe i have a IACV problem. Since my idle is flacutating.Sometimes it idles great at 830-850rpm. But after driving for a little it idles at about 1300 rpm and stays there and sometimes drops to 850 for a quick second. Motor idles smooth regardless what rpms its at. When I tried to check the timing using the proper procedure, my idle is above 1k with tps dc'd. I screwed the idle screw all the way down and unplugged both connecters that go to the iacv and the car dies when I start it. The way I have to adjust my timing is follow the proper procedure, then dc the iacv and of course the tps, turn on my headlights and rear defroster to get the idle down. I am in the process of getting another iacv. I was told this can cause bad gas mileage. And I know its a problem because its the same iacv from my N/A motor and it did exactly the same thing its doing now when I need to adjust my timing and my N/A was getting just as worst mileage as my turbo motor. But I want to see other opionions before I make the purchase.

Sorry for the long reading, but I wanted to explain everything cause last time I posted something on g20.net about my gas mileage when I was N/A I was treated like I was stupid and recieved NO HELP AT ALL. Thank you

Do you have a boost gauge? How often do you get into the 0psi and psi area? On a turbo motor you can stay under 2k rpm, but if you get into PSI area's you will be chugging gas.

11.1 AFR is not bad for in boost. 12.4 is dangerous though.

Go side gap your spark plugs, I got 2-3 more mpg with sidegapping.

Keep your foot of the throttle though, when my wife drives my na P11 she gets 24mpg, I get 20 .

I would start by using the word worse instead of worst

Try and set your idle screw back to where it was at first. That is not what you want to adjust it will just make the problem harder to diagnose. I think you want your idle at right around 900rpm once the car is warmed up. High idle will defiantly ruin your MPG at stop lights.

Next try only putting in 4 gallons of fuel at a time and then driving until the low fuel light comes on. That way you can get a more consistent idea of your fuel consumption. The fuel gauge isn't that accurate, especially at partial tank readings. Oh and get a note pad and keep track when you fill up if you are not doing this already. It is easy to make mistakes or forget.

I always idled my SR20's at 800-850 with no issues. That is the factory spec idle speed too.

Jere is right though, the fuel gauge is as accurate as the coolant temperature gauge. What I do is, drive until the first quarter, then fill up. This is about 3.5-4 gallons on a P11.

My sentra and 200sx both idle like that. Sometimes it'll idle at the right rpm and then sometimes it will be a little over 1k..
Also like Vadim said, could be your driving lol my bro got high 20's to low 30's in my 200sx but when I drive it I get 24-25 :o

I do have a boost gauge. Its actually the AEM truboost controller that shows boost also. I barely go to 0 psi area. Only if I was speeding up to the speed limit or to pass someone not going the speed limit. I will wait til my gas light comes on and try that 4 gallon thing. Yea i just saw my post, worst? LOL, I was at work using a state government computer and was in a rush to type it up. I swear, I've been really careful on how I drive to log my miles the past couple weeks.

You don't have to drive it until it's empty (light). Just fill it up full, reset your trip odometer, then drive till quarter tank then fill up, and write down the gallons/miles it took.

thats what i was doing. i always filled my tank up at quarter tank. i'm going to do some more tuning up and what not since today is my friday at work.

If you drive until the light comes on you will see how far off that gauge is when it says 1/4 tank. Sometimes I find about another gallon, sometimes not I dunno though maybe it's worse on certain cars?

On P11 I noticed with the light on it's about 2-3 gallons. 16 gallon tank, light comes on around 12.5gallons. It just doesn't really matter when the light comes on. You should avoid getting the tank that empty anyway. More room for liquid fuel to turn into gas fuel.