HELP -- Car Mileage Question....(Infiniti Q45t)

[Powerhouse]

I drive a Q45 and only average 260 miles (at best) from a full gas tank till empty...I recently read that the averages should be at 342 mi / 470.8 mi.** ( road/ highway ) I know things like tire air-pressure, weight on board, and how heavy footed you are make a difference... but my tires are fine, I have no problems with my engine nor do I have a lead foot. Whats going on here? why is my gas mileage so terrible? my gas tank is 21 gallons and I get 260miles per tank at best. once again i drive a Infiniti Q45 4.1 liter V8 ....Not a hummer H1 lol.

**When I say averages, I mean the averages for my car specifically.

[goody90q45]

You should be getting close to 15 mpg city/21 mpg highway. The 11 mpg your getting gets expensive quick.

Check the function of the O2 sensors. A 10-12 year old engine will be due. They'll cut into your gas mileage and often don't light up the CEL. Any ECU codes? Stumbling during acceleration (coils)?

[Q451990]

to NICO!

You need actual MPG numbers. Unless you're running your tank down to dead empty, you're not putting 21 gallons in at fill-up. I would start actually measuring the miles driven and gallons you put in to fill up and make sure things are as bad as you think they are. Mike is right though - O2 sensors are good starting point if you're below what you'd expect.

Heath

[elwesso]

You also made no mention of what your driving cycle is on your 260 miles...

I would usually get about 12MPG when i was driving to school everyday, about 5 miles each way...

[Powerhouse]

I was told in another forum that it could be something to do with the "fuel sending unit" or "fuel gauge cluster". Not 100% sure if my gauge is reading correctly sooo my plan as of now is to run my car till I run out of gas completely and record how many miles I go after the gas light comes on. How do I check the 02 sensors?

[goody90q45]

Rather than drive until she sputters, take the practical approach and look up fuel level sending unit and low fuel warning in the index of the FSM. One of those two places should tell you when the warning comes on.

http://www.nicoclub.com/FSM/Q45/1999_Q45/

In the meantime the scientific approach would be to reset the trip odometer to zero the next time you fill up and take note of the miles driven and gallons used on the fill up after that. Do the math and you have your answer.

Where's Andy?

Welcome to NICO!! Few of us would own Q's if it wasn't for the help we get here.

[elwesso]

Welcome to NICO!! Few of us would own Q's if it wasn't for the help we get here.

Indeed..... and BTW goody I got your idler and my Q all put back together, and Im back to terrorizing the streets once again, one lift of the clutch pedal at a time...

[BadQ45t]

I have a 97' and the fuel gauge is very conservative. I hit the "E" around 260-280 but the car will only take 16-17 gallons of gas.

I have owned my 97' since 200, I can tell you that I have NEVER EVER gotten anything close to 450 miles to a tank. I have hit 400 on a tank and still had two gallons left, so perhaps you could get around that but this is not a good car for gas mileage. We only have a 4 speed transmission and I guess for me my right foot is too heavy to really get anything close to great gas mileage. The 2nd gen was rated slightly higher then the 1st gen for gas mileage, but if I have never done better then 21 MPG EVER from day one.

[goody90q45]

........and BTW goody I got your idler and my Q all put back together, and Im back to terrorizing the streets once again, one lift of the clutch pedal at a time...

Glad to hear the pulley worked for you. Did I sent the correct washer set too?

You need to trade the Beast in for a peppy early 90's G20 before you get yourself in trouble......

[elwesso]

Lets just say, I got everything to work...

Back to the original topic... I have seen 450 miles in a single tank on my car... The G50 holds 22.5 gallons, and I put in like 21.5, so thats about as low as I wanted to go, and the route I took had like a 100 mile stretch of no gas stations believe it or not...

Have I mentioned since I switched to the 5 speed I have seen 25MPG

[oldmako]

I tend to drive at 80 on the interstate and I always get just over 20mpg. The few times I have intentionally driven it at around 60-65 the mileage jumps to 22-23mpg.

I don't generally stomp on it to get to cruise speed, I just allow the thing to get there with normal, perhaps even slow acceleration because I feel that impacts the mileage the most.

I never let the tank get below 1/3 before refueling.

If I wail on it, the mileage sucks but the smileage increases.

[loystock]

My average is 13 MPG city; 21 MPG highway; and 16 MPG combined in NORCAL. Yes, you can easily get over 22 MPG but the difficult part is driving below 65 MPH. I normally use Shell Premium and refill when it approaches 1/4 tank. Always use the trip odometer and amount of gas put in to calculate gas mileage.

[elwesso]

Yes, you can easily get over 22 MPG but the difficult part is driving below 65 MPH.

In my experience......... its not worth it...

[tfitzs01]

Before I replaced all the injectors in the Q, it was getting only 14 mpg on the highway downhill with a tailwind... now, it gets easily 22 mpg.

Just seems logical to examine all the fuel delivery components. Everything from the fuel pump and out to the O2 sensors. Quite a bit to check...

[Powerhouse]

----------------------UPDATE------------------------------

I noticed than when I fill up im only putting about 16 gallons of Saudi water in the tank....but when I do, tank reads full. Im averaging about 15 MPG, still not so good. What do I need to fix so my tank reads what I actually have in there??

[loystock]

Not that bad as It depends on how much of city driving and stop-and-go traffic are involved in your average. Try adding a bottle or two of Redline SI-1 Fuel System Cleaner to a tank of gas, if you have not done so.