06 67k Miles poor gas milage

[Pilgrim]

If the simple basics like air filter and tire pressure are good and the plugs have thousands of miles to go before being due to change, I'd start thinking about the possibility of back pressure in the exhaust system or an O2 sensor that's out of range and sending bad info to the ECU. An O2 sensor should throw an error message, but changing them with generic sensors would be a lot cheaper than changing plugs or messing with cats. AN O2 sensor is a very simple unit and doesn't require a factory replacement.

I admit these are simply guesses. If the converters are becoming plugged for some unusual reason, the problem should get worse over time - it doesn't require quick action, but observation.

[Eric L.]

Believe it or not, it is a myth for modern cars that a dirty air filter will cause a significant drop in fuel economy. The amount that modern filters flow even when significantly clogged is more than enough for a modern engine's electronics to compensate for. In fact, Pat Goss on Motorweek stresses this point over and over again.

As for the drop from 22 to 19mpg - that is not dramatic enough to immediately resort to thinking there is a CVT issue or fouled plugs, to be honest. Seasonal variations in fuel mixtures and just a little bit more cold weather idling can have a dramatic effect on gas mileage. I've found that just a little added wind blowing the wrong way can affect the mileage substantially as well.

Regarding the spark plugs improving mileage, that is also for the most part a myth - modern vehicles equipped with high powered ignition coils can compensate for older plugs by just upping the voltage delivered to the plug - there is a substantial margin that these can operate. When I had my plugs changed at 90k, the plugs were in pretty good shape. Sure they were not as new, but I had no reason to believe they performed any worse than new. Change in mileage? Absolutely none. I changed them just because I did not want them "to become one with the engine block" as the Cartalk brothers would say.

[Carguy75]

Originally Posted by Eric L.

Believe it or not, it is a myth for modern cars that a dirty air filter will cause a significant drop in fuel economy. The amount that modern filters flow even when significantly clogged is more than enough for a modern engine's electronics to compensate for. In fact, Pat Goss on Motorweek stresses this point over and over again.

As for the drop from 22 to 19mpg - that is not dramatic enough to immediately resort to thinking there is a CVT issue or fouled plugs, to be honest. Seasonal variations in fuel mixtures and just a little bit more cold weather idling can have a dramatic effect on gas mileage. I've found that just a little added wind blowing the wrong way can affect the mileage substantially as well.

Regarding the spark plugs improving mileage, that is also for the most part a myth - modern vehicles equipped with high powered ignition coils can compensate for older plugs by just upping the voltage delivered to the plug - there is a substantial margin that these can operate. When I had my plugs changed at 90k, the plugs were in pretty good shape. Sure they were not as new, but I had no reason to believe they performed any worse than new. Change in mileage? Absolutely none. I changed them just because I did not want them "to become one with the engine block" as the Cartalk brothers would say.

It is a myth to say that old plugs will give the same gas milage as new plugs and the wind will cause a sudden loss of 3 MPGs due to wind resistance, especially over a lengthy period of time. What we "all" are doing is giving an opinion of what we think the problem is and how to fix it. These ideas are opinions. No one can diagnose an owner's particular car problem over the web with 100% accuracy, too many variables. So, please stop trying to make every suggestion a debate about myth vs. fact. In addition, your theory about modern coil packs compensating for worn plugs is the biggest myth. The coils can compensate enough to avoid misfiring, but still produce a weaker spark than it would with a properly gapped plug or new plug with the correct gap. The car cpu can only compensate so much for poor performing items like worn spark plugs and dirty air filters. These items has to be changed, sometimes before the manufactor's recommended time. That is why Nissan "recommend" and not make it a set time because the items can last longer or fail sooner than the time Nissan recommends them to be changed.

[Pilgrim]

OK then, my opinion:

- Change in gas mileage does not warrant plug change at this mileage. IMO plugs aren't at all likely to be a problem. Even with older ignition systems, I have changed plugs which were worn considerably wider than spec and no gas mileage loss had occurred.
- Primary culprit IMO is cold weather.
- Alternate culprit is the gas - mixtures change from winter to summer and winter gas often gets lower mileage.

I'd make sure the air filter is clean (can't hurt, may help), air up the tires to customary pressure and drive it until the weather warms up.

[Eric L.]

Originally Posted by Carguy75

It is a myth to say that old plugs will give the same gas milage as new plugs and the wind will cause a sudden loss of 3 MPGs due to wind resistance, especially over a lengthy period of time. What we "all" are doing is giving an opinion of what we think the problem is and how to fix it. These ideas are opinions. No one can diagnose an owner's particular car problem over the web with 100% accuracy, too many variables. So, please stop trying to make every suggestion a debate about myth vs. fact. In addition, your theory about modern coil packs compensating for worn plugs is the biggest myth. The coils can compensate enough to avoid misfiring, but still produce a weaker spark than it would with a properly gapped plug or new plug with the correct gap. The car cpu can only compensate so much for poor performing items like worn spark plugs and dirty air filters. These items has to be changed, sometimes before the manufactor's recommended time. That is why Nissan "recommend" and not make it a set time because the items can last longer or fail sooner than the time Nissan recommends them to be changed.

The folks who have been here since the site started will know I am a total maintenance nut - I tend to replace everything well before its time. I like to think my engine is running at 100% efficiency if I take care of the maintenance before it is due. However, I am under no illusion that doing so will dramatically influence the amount of power the engine makes, or its fuel efficiency. 1%, sure. But 3mpg, impossible unless I have a misfiring cylinder and an intake leak.

In the case of the OP's question, I do not object to suggesting proper scheduled maintenance of the vehicle. However I don't believe for a second that it will make up for a substantial portion of the lost fuel economy, when more obvious explanations such as cold weather, winter fuel formulation, and the effect of wind resistance come into play. Keep in mind that the majority of increased fuel consumption at highway speeds is due to overcoming wind resistance. If you have a headwind, that will dramatically diminish fuel economy in a tall vehicle like the Murano.

[Carguy75]

Originally Posted by Eric L.

The folks who have been here since the site started will know I am a total maintenance nut - I tend to replace everything well before its time. I like to think my engine is running at 100% efficiency if I take care of the maintenance before it is due. However, I am under no illusion that doing so will dramatically influence the amount of power the engine makes, or its fuel efficiency. 1%, sure. But 3mpg, impossible unless I have a misfiring cylinder and an intake leak.

In the case of the OP's question, I do not object to suggesting proper scheduled maintenance of the vehicle. However I don't believe for a second that it will make up for a substantial portion of the lost fuel economy, when more obvious explanations such as cold weather, winter fuel formulation, and the effect of wind resistance come into play. Keep in mind that the majority of increased fuel consumption at highway speeds is due to overcoming wind resistance. If you have a headwind, that will dramatically diminish fuel economy in a tall vehicle like the Murano.

So, it is your "opinion" that it may the cold weather as opposed to maintance that is causing the drop in MPG. You can give an opinion without saying someone else opinion is wrong. That is my point. Therefore, we all can be right or wrong.

[Carguy75]

Originally Posted by Pilgrim

OK then, my opinion:

- Change in gas mileage does not warrant plug change at this mileage. IMO plugs aren't at all likely to be a problem. Even with older ignition systems, I have changed plugs which were worn considerably wider than spec and no gas mileage loss had occurred.
- Primary culprit IMO is cold weather.
- Alternate culprit is the gas - mixtures change from winter to summer and winter gas often gets lower mileage.

I'd make sure the air filter is clean (can't hurt, may help), air up the tires to customary pressure and drive it until the weather warms up.

Well after rereading the OP concern about the CVT in relation to the drop in MPG, I believe that we both are barking up the wrong tree on this question. I believe he is more concerned about the CVT having a problem than the actual loss in gas mileage. P.S. opinions are like assholes, every one has one.

[Eric L.]

Originally Posted by Carguy75

So, it is your "opinion" that it may the cold weather as opposed to maintance that is causing the drop in MPG. You can give an opinion without saying someone else opinion is wrong. That is my point. Therefore, we all can be right or wrong.

I'd go with what is more likely to be the problem, rather than a less likely cause. As I wrote above, I have nothing against a spark plug change - I just think it has very little to do with the mileage drop the OP reported.

[Pilgrim]

Originally Posted by Carguy75

Well after rereading the OP concern about the CVT in relation to the drop in MPG, I believe that we both are barking up the wrong tree on this question. I believe he is more concerned about the CVT having a problem than the actual loss in gas mileage. P.S. opinions are like assholes, every one has one.

Very possible! In that case, it would be worth taking the car to a dealer for the Consult-tool analysis of the CVT oil.

[Carguy75]

Originally Posted by Eric L.

I'd go with what is more likely to be the problem, rather than a less likely cause. As I wrote above, I have nothing against a spark plug change - I just think it has very little to do with the mileage drop the OP reported.

And I believe that spark plugs could be a more likely factor in mileage drop considering the OP said that the mileage dropped recently this winter, but his Murano had better gas mileage during previous winters. So, this is a new problem this winter only.Therefore, the OP would have noticed a MPG drop during previous winters. So that rules out cold air as being the only cause of decreased MPG or wind resistance.Unless, this year the OP area is have an usually case of strong winds this year compared to previous years. A winter el Nino! Just kidding!

[Pilgrim]

I won't argue, just note that I don't have the same faith that plugs may be the cause.

[njjoe]

Originally Posted by Pilgrim

Very possible! In that case, it would be worth taking the car to a dealer for the Consult-tool analysis of the CVT oil.

I believe that would prove little, if anything, about the condition of the CVT.

The CVTF Deterioration Date is nothing more than an algorythm that attempts to calculate the theoretical remaining life of the fluid.

Plus, I doubt many serice managers even know about the CVTF Deterioration Date. Mine did not.

-njjoe

[njjoe]

Originally Posted by Eric L.

The folks who have been here since the site started will know I am a total maintenance nut...

A resounding YES to that.

-njjoe

[nitely]

Too early for new plugs. It would be a waste. I would just set the tire pressure a little above recommended, drop a bottle of fuel system cleaner in the gas tank and observe. Wait till you get the summer blend and check your mpg again. 19 mpg is soooo average for city driving. I even consider 15-20 mpg range to be city average.

Your jerky deceleration if accompanied by any hesitation maybe cvt related or throttle related. So observe carefully. You do know the Normal forward jerk - when the torque converter releases - you get when you are stopping right? And its not that? Good luck.

[Carguy75]

Originally Posted by Pilgrim

I won't argue, just note that I don't have the same faith that plugs may be the cause.

I will not argue neither, but I have faith that plugs could be a cause. P.S. This last word thing we have going on could go on forever.