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LTFT figure stuck at 0 and Bad fuel economy? 2013 Nissan Rogue

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12 Mar 2020 13:18 #38285 by TorJoe
Hello,

I recently bought my 2013 Nissan Rogue used and have just realized that it does not produce any Long Term Fuel Trim data for my scan tool. When I use my scan tool to read for LTFT it's always 0. It does produce Short Term Fuel Trim data. I have already tried resetting ECU and been driving the car for more than 100 miles since the reset, but still no sign of LTFT data.

Potentially connected to this is the fact that my car has very bad fuel economy. I have read somewhere that LTFT stuck at 0 may have to do with EVAP problems (somewhere a sensor is not sending signal to the ECU), which can cause bad mileage because a bad EVAP valve can have the effect of a vacuum leak (air-fuel mixture gets vented outside instead of being routed back to the combustion chamber, thus creating a lean condition).

My A/F wideband oxygen sensor does report frequent lean spikes once RPM goes above 1500.

Anyone has any idea as to what the meaning of all this is? I'd appreciate greatly any input from you. Thank you!

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12 Mar 2020 14:08 #38286 by tech25
what kind of scan tool are you using??

Also, are you using obd, or vehicle specific parameters when looking at pids??

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12 Mar 2020 14:27 #38287 by TorJoe
Hi,

I use BlueDriver. I believe the parameters used are OBD.

I am attaching a combo chart of my STFT and RPM readouts. The blue line is STFT. As you can see, there are very frequent 25% lean spikes. The orange line is RPM. It seems that the lean spikes occur when RPM climbs above 1500. I don't know if there is a real causal relationship behind this seeming correlation.

https://imgur.com/a/6UxOia2

Since I bought my car I have done the following maintenance work:
1) Engine oil + filter change
2) Air filter change
3) MAF cleaning
4) Spark plugs change / Coils checked (all good)
5) CVT fluid change

None has helped my fuel economy.

I have not carried out a vacuum check as I have read at several places online that vacuum leaks tend to have its greatest effect at idle (and that their effect reduce as RPM goes up), but my lean spikes seem to occur only when RPM and vehicle speed increase.

So I am now inclined to think that my bad fuel economy originated from either a EVAP or a fuel-supply-side issue - something that kicks in once RPM rises to a certain level.

I am only a novice DIYer so I'd appreciate some guidance. Thanks.

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12 Mar 2020 14:29 #38288 by TorJoe
Sorry I don't seem to be able to integrate the chart directly into my post.

But my STFT + RPM and SRFT + Vehicle Speed (km/hr) are here:

imgur.com/a/irFu7Ux

Thanks

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12 Mar 2020 15:36 #38291 by Weycraze
I'll Chime in on the Bluedriver use;

It is very possible the Bluedriver is not picking up the LTFT. If you are using the latest firmware, try rolling back version by version until the LTFT shows up. IF, you have access to another scanner, try it to compare.

Also, before you try rolling back, try it on another vehicle to see if the LTFT is there. After every update/rollback reset the apps data/storage.

As good as the BD is for global OBD it sometimes has a few caveats. I have seen a few new firmware updates that were not good and BD support said to roll back until they figured it out, which was rather quickly.

Paul

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12 Mar 2020 16:53 #38293 by Tutti57
Is there a PID for Alpha b1? That's basically Nissan's total trim. 100 is stoich, over 100 is lean and under is rich. +/- 8 to 10 is acceptable range.

How about an A/F sensor b1 pid? Looking for 2.2v with close fluctuation to that number. Can you force that number to go up by pulling a vacuum line? You should be able to make the alpha go up the same way. Stuck at 2.2v could mean a sensor problem.

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12 Mar 2020 18:57 #38294 by TorJoe
Hi,

The AF sensor does have a readout, and the figures do tend towards 2.2 volts (but they do not get stuck there), with sharp lean spikes (all the way to above 4.5 volts) that correspond with the positive STFT spikes. Please see the following chart.

imgur.com/a/kswaPBX

I will have to ask around before I can find another car to try my BlueDriver on.

I have also posted my MAF and RPM chart at the link above. It seems that MAF and RPM do correlate with each other, though I can't tell whether the correlation is as proportionate as it should be.

Thank you.

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12 Mar 2020 20:21 #38295 by scannerjohn
I have to say, I'm not a big fan of data streams while driving. Your RPM are all over the place which make it harder to interpret the data.
Voltage when it comes to A/F sensors and scantool values are an interpreted value by the scantool. The stoichiometric ratio of 14.7.1 in voltage for Nissan is 1.47v and changes in value are measured in current not volts but the scantool will show that interpreted voltage value.
Can you post a graph of RPM, STFT and LTFT at idle then increase RPM to 1500 then 2500. Please do not overlay the data.


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12 Mar 2020 20:31 #38296 by TorJoe
Scanner John: Do you want me to hold my RPM at each of those levels for a certain length of time (say 30 secs or 1 min) before graduating to the next level?

As for the stoichiometric voltage for the B1S1 wideband oxygen Sensor, according to my service manual, as Tutti57 pointed out, it is 2.2 volts. But I am a novice so maybe I am confused about the whole current-voltage thing.

Thank you

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12 Mar 2020 20:36 #38297 by TorJoe
And, also, the reason I provided the readouts from when the car was moving rather than at idle is because those lean spikes appear only when the car is moving (at moderate and high speed).

In any case, I will get you some charts of my car at idle tomorrow.

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12 Mar 2020 20:41 #38299 by scannerjohn
yes hold the rpm's want to see what stft does, so if it keeps moving at 1500, hold until it levels then go to 2500.

I recorded the 2.2v in my records so I will confirm and update...


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12 Mar 2020 21:35 #38303 by Tutti57
1.5v was the calculated value on older models. 2.2v is what you will see. Is the Alpha pid available on your tool?

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12 Mar 2020 22:41 #38305 by TorJoe
Tutti57: sorry, missed that bit about Alpha pid (you mean the air-fuel ratio parameter where 100 = 14.7:1?) . I have not noticed it as supported on my scan tool (or by my car). But I will check tomorrow (I live in a high-rise and my car is in the underground garage so I don't have ready access to it). I do know my scan tool and car support lambda (BlueDrive calls it equivalence ratio, but I suppose they are the same thing, no?).

In any case, the lambda readout correspond with the AF sensor readout with all its lean spikes.

I have added the lambda chart to the bottom of the same link:
imgur.com/a/kswaPBX

I will get some at-idle charts tomorrow. Night-night.

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12 Mar 2020 22:55 #38306 by TorJoe
Scanner John: one thing, about the idle readouts, should I record them when the car is at operating temperature, or if it doesn't matter even if it is a cold start?

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13 Mar 2020 12:16 - 13 Mar 2020 12:18 #38310 by scannerjohn
operating temp...system closed loop.


Last edit: 13 Mar 2020 12:18 by scannerjohn.

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13 Mar 2020 18:03 #38313 by Tutti57
The Alpha pid is Nissan's version of fuel trims. I was just thinking that it might be another way of seeing what's going on if the long term isn't showing properly. I've never seen it shown as anything besides Alpha but it would be enhanced data instead of global OBD2 and I'm just not familiar with that scan tools features are.

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13 Mar 2020 20:00 #38317 by TorJoe
Hi, Blue Drive does claim to support enhanced diagnostic, but I don't see the Alpha PID.

And I don't have the idle charts to show you yet. I examined the PCV valve today and found the stopper inside to be not rattling freely as it should. I have installed a new one and have yet to test drive the car to see if it makes any difference.

I'll see if I can do the idle rev tomorrow.

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