New the the Board: Gas Mileage Question/Intake Question

[MOG35]

Hello all!

I have an '04 G35x with approx 51K miles. Over the last few tanks of gas, my mielage has been horrendous (around 10mi/gal). I had a full diagnostics/fuel system check and everythink was ok. Was running a touch lean but no other issues.

Recently replaced the dirty air filter with an K/N drop in hope to free up air. So what could be causing the problem???

Also, is an air intake system good for boosting mpg and performance. I have the drop in and have also heared of z-tubes. LMK!

Thanks!

[Tampa G35 Sedan 6MT]

z tube will help performance and make it sound better (louder)

Are you running premium? where is the gas from?

How is your driving style... You should run som lucas fuel system cleaner... You could have some clogged fuel injectors..

DJ

[MOG35]

z tube will help performance and make it sound better (louder)

Are you running premium? where is the gas from?

How is your driving style... You should run som lucas fuel system cleaner... You could have some clogged fuel injectors..

DJ

I dont have a heavy foot...anymore. Was running silver (mid grade) from BP but switched to Premium. Can I get Lucas system cleaner at any general auto parts store?

With the Z tube, will have have to switch out the stock air box and K/N drop in?

thanks!

[GAU-8]

Running lean and getting crappy gas mileage don't work together. Possibly a clogged fuel filter or clogged injectors for the lean issue. But the crappy gas mileage could also be fouled O2 sensors. If you're serious about getting things clean, there's only one way to go. That is BG fuel system cleaners. They have stuff for the tank and for the top end of the motor. The top end cleaner might need to be done at a qualified repair center as it has to be fed through an intake vacuum line to clean the intake tract below the plenum all the way to the valves. But there is a BG fuel system cleaner that goes in the tank. I would recommend putting that in only after changing the fuel filter first. Otherwise the fuel system cleaner won't be used to its full capabilities.

[telcoman]

Hello all!

I have an '04 G35x with approx 51K miles. Over the last few tanks of gas, my mielage has been horrendous (around 10mi/gal). I had a full diagnostics/fuel system check and everythink was ok. Was running a touch lean but no other issues.

Recently replaced the dirty air filter with an K/N drop in hope to free up air. So what could be causing the problem???

Also, is an air intake system good for boosting mpg and performance. I have the drop in and have also heared of z-tubes. LMK!

Thanks!

Crappy gas mileage can also result from the type of driving that you do.

Check your tire pressure.

How much weight are you carrying around in your trunk?

Here is an example of the wife using my G for short trips of 2 miles or soon trips to Florida.





I also did a study of using Premium 93 and midgrade 91 against the use of regular. I found no significant increase in MPG for my one month test of each and went back to regular 87 octane.If I were you prior to messing with fuel filters etc fill your tank. Drive 200 miles non stop at 65 to 75 MPH on cruise control.

Refill your tank and divide the gallons it took to refill the tank into the miles traveled. I'm fairly confident you will see a substantial increase in MPG.

By not changing your air filter regularly and allowing it to get very dirty, you may have a MAF sensor problem?

BTW who performed the diagnostic test? Was it done at a dealer?I don't trust independent shops.

Good luck

Telcoman

Modified by telcoman at 1:37 PM 10/11/2009
Modified by telcoman at 1:38 PM 10/11/2009

[MOG35]

The dealer ran the diagnostics. I am going to follow up with them tomorrow to see if they ran the MAF sensor check.

Another question, I get a z tube (calling a Nissan dealer to save $$ ), where does the sensor/wiring harness hook into?

Is there a distinct sound difference.

[Tampa G35 Sedan 6MT]

Let me ask you this... how do you caluclated your mileage?

How many miles are you getting from a full tank to when the gas light comes on?

I get about 300-350 with most city driving... that is anywhere from 18-22 mpg assuming you get gas right when the light comes on.

The Z tube is the tube between the stock air box and the throttle body. It will mount right in..

DJ

[SVTCOBRA]

I was surprised to see the MPG go down slightly in our 05 Sedan after adding a K&N drop in. I've seen increased in other vehicles. But, K&N doesn't claim to increase MPG.

[MOG35]

Last tank, I got 210 mi total. This is after I took it to the dealer for checks.

[GAU-8]

Telcoman, your lowest mpg was in the 16ish range. He's talking 10 mpg. You could fill that car with 5 people and a trunk full of luggage and not get that bad of gas mileage. I'm only on my first tank since buying this car and have 220 miles on it with the needle just shy of half tank. I too drive short distance 5 days a week. I'm military living in housing on base. My commute to work is less than 2 miles. Hardly enough time for the O2's and motor temp to do their thing. Of course, I'm also bone stock including air filter. I would start with the simple stuff. Change fuel filter, run fuel system cleaner through tank and injectors. Then re-check. If it's still bad, I'd be knocking on the dealership's door. There is no reason for his numbers to be that low.

I know I'm the new guy so don't take what I write as barking or harassing anyone. I'm trying to get in where I fit in. I have done some basic tuning, however, not on a Nissan platform. But the principals generally remain the same.

On a side note, I'm curious how they deduced his lean condition? A dead plug or coil pack can cause crappy mileage but run rich fuel, as the injector is still working. If he has a clogged injector, the cylinder is still seeing a spark with no fuel. That would show lean so the computer should attempt to fatten the fuel until it can get readings within limits. So if 5 cylinders are firing fine but with a rich mixture, it could still theoretically be lean and wasting fuel at the same time. Just thinking out loud via my keyboard. What say you all on this thought?

[telcoman]

Telcoman, your lowest mpg was in the 16ish range. He's talking 10 mpg. You could fill that car with 5 people and a trunk full of luggage and not get that bad of gas mileage. I'm only on my first tank since buying this car and have 220 miles on it with the needle just shy of half tank. I too drive short distance 5 days a week. I'm military living in housing on base. My commute to work is less than 2 miles. Hardly enough time for the O2's and motor temp to do their thing. Of course, I'm also bone stock including air filter. I would start with the simple stuff. Change fuel filter, run fuel system cleaner through tank and injectors. Then re-check. If it's still bad, I'd be knocking on the dealership's door. There is no reason for his numbers to be that low.

I know I'm the new guy so don't take what I write as barking or harassing anyone. I'm trying to get in where I fit in. I have done some basic tuning, however, not on a Nissan platform. But the principals generally remain the same.

On a side note, I'm curious how they deduced his lean condition? A dead plug or coil pack can cause crappy mileage but run rich fuel, as the injector is still working. If he has a clogged injector, the cylinder is still seeing a spark with no fuel. That would show lean so the computer should attempt to fatten the fuel until it can get readings within limits. So if 5 cylinders are firing fine but with a rich mixture, it could still theoretically be lean and wasting fuel at the same time. Just thinking out loud via my keyboard. What say you all on this thought?

Since the vehicle was at the dealer I would think that if something was wrong they would have found it/

I have one of these that are not expensive.



Short trips, idling for long periods of time, tires dragging brakes, who knows?

You are getting decent mileage with 220 miles at the 1/2 tank mark.

With the needle square on the 3/4 mark after a fillup 120 to 130 miles is good MPG. 220 to 250 at the 1/2 mark and 320 to 350 at the 1/4 mark will usually result in over 25 MPG. After almost 4 years and 99k miles I know my G pretty well.

I do know that being stuck in bumper to bumper stop and go traffic can really kill your MPG.If you look at my table the entry for 14 September show my MPG at 23.65 vs the previous entry of 27 August of 25.77 MPG and the next entry on 17 Sept of 25.27 MPG

Why did I get 23.65 MPG?

Because there was a multiple vehicle accident on the Garden State Parkway shutting down the parkway for 1 hour and my G was idling for most of that time.

I think the dirty air filter may have messed up the MAF but there are experts around here that may have other suggestions.

Telcoman

[MOG35]

all these ideas are great. Keep them coming....

[GAU-8]

I'd love to get one of those scanners. I have an OBDII code reader for MILs from Actron. That might be nice to have since I don't have diagnostic monitoring software anymore. I'm picking up what you're putting down. Just thought 10 mpg is indicating bigger problems than just a long idle time or faulted MAF. Nearly every car I've owned that has run on MAF calibration would pop a MIL if the frequency was out of spec. His would have to be way out of spec to get such piss poor mileage. As far as the OP, try some of Telcoman's suggestions and look at tire wear, pressure, brake slack, etc. Lift a wheel off the ground and try to spin it. It should move at least 1 full turn before stopping. If it locks right up, it's a good possibility you're dragging a brake. Other telltale signs would be excessive dust on on particular wheel.

[Tampa G35 Sedan 6MT]

I am still thinking that you are not calculating the MPG correctly!

I don't think i have ever gone below 15 mpg and I drive like a freak!

DJ

[MOG35]

doesnt take a genius to run this equation

210 mi/18gal = 11.67 mi/gal. Not exactly 10 but still horrendous.

Current tank is approx 3/16 gone and I have only 39.5 miles

Sooo. ..1875(18 gal) = 3.375 gal39.5 mi/3.375gal= 11.7 mi/gal currently

everytime I start my engine, my gas gauge drops approx 1/16th-1/8th of a tank and barely recovers.

Modified by MOG35 at 6:12 AM 10/12/2009

Modified by MOG35 at 6:13 AM 10/12/2009
Modified by MOG35 at 6:14 AM 10/12/2009

[Tampa G35 Sedan 6MT]

I know this sounds carzy but maybe the float in the tank is bad and the gas light comes on when you really have like 7-9 gallons left...

Oh wait stupid question... You did say you can pump 18 gallons or close to it right?

DJ

[MOG35]

I know this sounds carzy but maybe the float in the tank is bad and the gas light comes on when you really have like 7-9 gallons left...

Oh wait stupid question... You did say you can pump 18 gallons or close to it right?

DJ

Correct. I am connect back with the Infinit service dept today to drill into what they specifically checked. Want to see if they checked all fuel injectors, oil seals, and the MAF sensor.

[Tampa G35 Sedan 6MT]

Yes please keep us posted..

I really want to know the answer to this question!

DJ

[MOG35]

so do I

Update: spoke with the dealer today an they said their data showed no issues at all with improper gas usage by the engine, leaks, MAF issues, etc. Suggested I run another full tank, document the mileage, fill up again then bring it to them for another battery of tests.
Modified by MOG35 at 11:53 AM 10/12/2009

[jmcohen23]

dumb question, but could there be a leak?

are you filling up at the same gas station each time?, perhaps you got bad gas (pun intended)....

there is a station near me that people got bad gas from, however, most of their cars would not even start up.

[telcoman]

dumb question, but could there be a leak?

are you filling up at the same gas station each time?, perhaps you got bad gas (pun intended)....

there is a station near me that people got bad gas from, however, most of their cars would not even start up.

I wonder if someone changed the plugs and installed the wrong ones?

[G_whizz]

My guess would be

Injectors or fuel filterBad gas (have you tried a different gas station?)Plugs as Telco said.

TelcomanI know I'm the new guy so don't take what I write as barking or harassing anyone. I'm trying to get in where I fit in. I have done some basic tuning, however, not on a Nissan platform. But the principals generally remain the same.

Your help is appreciated!!

[Tampa G35 Sedan 6MT]

I am just stumped....

I slooked over an old thread and couldn't find any answers...

heres the link with someone that had the same problem!http://forums.g35club.org/zero...39935

DJ

[MOG35]

It may have been bad gas, I wouldnt doubt that. I may change out the plugs just to be safe and b/c it doenst cost that much. I am going to run this tank out, fill again, and document mileage and see if there are any changes.

[Tampa G35 Sedan 6MT]

Make sure you get gas from some where that Has a High Volume Of gas that they go through each day... (sams) This way if it was bad gas they have such a high turn over on the fuel that you can rule it out if it was.

DJ

[kmckis1029]

when was your last oil change? i have notice when i get to the end of my oil change interval my gas milage drops... just a thought...

like many i have never gotten less than 16mpg and thats driving like i stole it... and i have the g35x also...

collectively everyone has named everything i would suggest as the problem...

hey!!! have you tried just reseting the ECU? (easy way... disconnect battery and pump brakes) this will give you all the base air/fuel maps...

[MOG35]

when was your last oil change? i have notice when i get to the end of my oil change interval my gas milage drops... just a thought...

like many i have never gotten less than 16mpg and thats driving like i stole it... and i have the g35x also...

collectively everyone has named everything i would suggest as the problem...

hey!!! have you tried just reseting the ECU? (easy way... disconnect battery and pump brakes) this will give you all the base air/fuel maps...

I have one coming up in 1K miles, but I think my last one was done poorly. I waswatching and it looks as they didnt replace any filters (oil/air).

I recently replaced the battery, but will reset the ECU like you mentioned. How many pumps?

[Tampa G35 Sedan 6MT]

Just leave the batt unplugged for about 5 min and that will do it!

DJ

[MOG35]

Sounds good.

[kmckis1029]

didnt replace the filter

well if a reset ECU with fresh oil, new oil/air filters, with intake/fuel injector cleaning. and no bad spark plugs doesnt improve your milage... then something is really wrong... and i would love to know the fix... cause it might be something we all should check on our cars...