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Discussion Starter · #1 ·
Hi,

Mine is a 2013 Nissan Rogue S. I bought it used a month ago and have since been trying to identify the source(s) of its very bad fuel economy, so far to no avail.

The car has its own dashboard fuel economy gauge and the figure shown is routinely around 17 liter/100km (~14 MPG) for city driving. The official MPG figures for the car model are in the mid-20s. So my car is nowhere near where it should be in terms of fuel economy, even when taking into account the conditions of winter driving.

Since coming into possession of the car I have replaced with high quality parts the following:

1)The air filter
2)Engine oil & Oil filter
3)Coolant
4)All the spark plugs

To better diagnose problems I have bought a BlueDriver OBDII scan tool to record live data from my car.

I notice the following irregularities in the data that may point to the root cause(s) of my car's poor fuel economy. But I am not sure how to interpret them. I would really appreciate it if people from this community could help me out with their ideas.

1)Frequent and abrupt spikes in the voltages of the Air/Fuel (B1S1 Wideband O2) sensor when driving. The stoichiometric voltage of my car is 2.2 volts. The A/F voltage of my car would shoot up, always abruptly, to 4 or more volts (i.e. extreme lean condition) multiple times during a 20-minute drive. Lambda jumps with it.

2)Every time there is a spike in the A/F voltage, the Short Term Fuel Trim would shoot up to compensate the lean condition. So in a short, low-speed 20-minute drive in the city the STFT would show multiple high trims (e.g. 25%).


3)The scan tool indicates a permanent code of P0102 "Mass or Volume Air Flow Sensor "A" Circuit Low." I have tried swapping the Mass Airflow Sensor that came with the car with another used MAF sensor. The same bad fuel economy has persisted. I have not yet tried installing a brand new MAF sensor because of its cost. I would like to eliminate other possibilities before investing in a new MAF sensor.

I have plotted the figures for RPM and MAF gram/second on the same chart and it seems to me that the MAF sensor readout basically tracks changes in RPM, so it's not obvious to me that MAF is malfunctioning (though I don't know for sure whether the sensor under-reports the amount of air entering).

And it doesn't seem to me that I have a vacuum leak problem as the sudden spikes in the A/F sensor voltage occur during driving, and from what I have learned online the effect of vacuum leaks is usually more pronounced at idle and declines as the car accelerates.


Please let me know your thoughts. As for myself, the following questions are swirling around in my mind:

(1) What can cause the voltage of the A/F sensor to spike abruptly as in the case of my car? I have read in multiple places online that these wideband O2 sensors don't change their voltage suddenly like the traditional oxygen sensors do. Is it normal for AF sensors to have sudden spikes at all?

(2) In connection with question one, I have read somewhere that sudden spikes in AF sensor voltage may have to do with a shaky ground wiring. If this is a possibility, how do I go about confirming or ruling it out?

(3) Can my bad fuel economy really be caused by a bad MAF sensor, given the P0102 code? Is it theoretically possible that a bad MAF sensor is causing the kind of AF sensor voltage and STFT fluctuations seen in my car?

I'd appreciate any input from you. Thank you!
 

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Look at freeze frame data for the conditions present when the code set. Let us know what they are.
 

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Discussion Starter · #3 ·
There is no data on the freeze frame page. The P0102 is always there as a "Permanent Code". And BlueDriver wouldn't let me clear it.

There is one further wrinkle I can tell you about: as I said in my original, I have swapped out the MAF sensor that came with the car with another used MAF sensor. Prior to that, BlueDriver had been giving me two codes, P0102 and a pending code of P0113 (Intake Air Temperature Sensor 1 Circuit High Bank 1). After swapping the MAF sensor I am now left with P0102. P0113 has disappeared. But the lean spikes are still there.
 

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There is no data on the freeze frame page. The P0102 is always there as a "Permanent Code". And BlueDriver wouldn't let me clear it.

There is one further wrinkle I can tell you about: as I said in my original, I have swapped out the MAF sensor that came with the car with another used MAF sensor. Prior to that, BlueDriver had been giving me two codes, P0102 and a pending code of P0113 (Intake Air Temperature Sensor 1 Circuit High Bank 1). After swapping the MAF sensor I am now left with P0102. P0113 has disappeared. But the lean spikes are still there.
Not sure about Nissan, but many cars have the IAT sensor integrated with the MAF sensor. Spiking MAF can cause all sorts of odd behavior. Can you map the sensor along with TPS and RPM and log the trip? You can then find out out how the MAF correlates with he other two. Should be a smooth relationship, all three going up together, though not completely linear. My wife's Windstar kept cutting out at idle when pulling away from stop. MAF was all over the place. Would be steady, then plunge when the TPS and RPM went up suddenly. Worked normally when driving. Went to the salvage yard, got one for $20, and that fixed it. I know it is tough to wing a $100 new part at a problem, but my $20 wager paid off.
 

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it almost sounds like there is a rip or crack in the air tube from the MAF to the throttle body. take it off and look at it closely. :vs_cool:
 

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it almost sounds like there is a rip or crack in the air tube from the MAF to the throttle body. take it off and look at it closely. :vs_cool:
Good idea. Air tubes develop cracks that sometimes only open when the engine warms up. Now you see it, now you don't.
 

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Discussion Starter · #7 ·
I am very grateful for your comments and advice.

About a possible vacuum leak: I have read at multiple places online where they say that the effect of a vacuum leak is most pronounced when the car is at idle. But my Air/Fuel sensor voltage lean spikes seem to take place only when driving at higher speed. Does this mean the chance of a vacuum leak is low?

By the way, I have posted a whole punch of charts here (MAF, RPM, A/F sensor voltage, post-cat O2 sensor voltage, catalytic temperature, timing advance for #1 cylinder etc) for those who has the interest to delve deeper. Please let me know if you see anything unusual in these charts that might explain my car's bad fuel economy.

https://forums.nicoclub.com/post6804180.html#p6804180

Thank you so much for your help!
 
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