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Lean Fuel Trim

Hi Everyone,

I have a 2006 Nissan Sentra SE-R Spec V. My short term fuel trim readings seem to be at about +7% idle, +5% to 9% under load, which the occasional +10% or so spike. Sometimes, load acceleration will be ±2%, and the idle will frequently settle at +/-2% but will oscillate back to +7%.

What’s curious is that the long term fuel trim reads 0.0% at all times, and doesn’t change. Is my scan tool producing an error, or is this long term fuel trim normal despite my short term fuel trim reading lean?

Thank you

Those numbers are not a problem.
Typically the CEL lights at 25%.
The fuel injectors might be a little dirty: toss a bottle of Techron in the tank.
Ethanol in the gas also has effect since it needs a different air/fuel ratio.

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Thank you for the information. Is it normal for the Long term fuel trim to always read 0.0% though? Even when STFT is reading higher numbers, LTFT will stay at 0.

My son has one of those. Have you modified it in any way such as a low restriction muffler or CAI or the NISMO cams? These mods will throw off your STFT, but usually the LTFT as well.

You don’t have a problem though, your vehicle is operating well within spec. If you haven’t cleaned the MAF sensor, you might do that but otherwise I would not do anything else at this time. Don’t do a Red Green here, “if it ain’t broke, fix it till it is.”

Hi Keith, the vehicle has a aftermarket header to address the problem with the pre-cats destroying the engine. But other than that, it is all stock!

Not being sure what kind of OBD reader you have I’d suggest you may have chosen the wrong PID for LTFT, bank2 rather than bank1, for instance. Anyway worth a double-check if it’s applicable to your device

IMG_0277b

Hi, it s a ThinkOBD 100 scanner, as shown in the photo.

Thanks

I see, I’m no expert on these things and I use a Bluetooth dongle version myself. On mine, after I load a yr, mk and model, I need to go through a data base of pertinent PIDs and select not only ones that I want but ones that there is output for coming from the onboard computer module. If I want oil temp, for instance, and I select that but if the car’s output doesn’t provide for that parameter the gauge will 0 or no data, etc.

Unless this is some sort of ‘thing’ for this model that it doesn’t have LTFT for reason unkown that LTFT should normally be dancing around along with the STFT.
Have you tried this reader on another car?
If it also doesn’t show LTFT on other cars I’d say you have a faulty OBD reader. If it does show on another car than the OBD port on your Sentra may be at fault, bad connection, broken pin, etc. Unless, of course, it’s a thing on this model. I like to see a STFT of less than 5. More begins to be problematic but you still should be showing some value other than zero for LTFT. Hope some of this long winded reply helps.

Hi Neburex,

It does, alot thanks. The scanner automatically sets the correct settings for the car. I was wondering why LTFT is reading 0, and I thought that wasn’t normal. I’ll look more into diagnosing the scanner or finding out about this specific model of Sentra.

Ltft is a universal PID for all cars. There is a group of universal PIDs and a set of vehicle specific PIDs. Compare another reader.

Sorry but I have to ask, what does PID stand for?

Parameter ID. Basically an identifier of the OBD thing you are trying to read.

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Thanks Mustangman. I also contacted the manufacturer of the scanner, and they said that LTFT should be fluctuating. I’m going to try another scanner today.

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When you installed the new header, you had to move both O2 sensors downstream. Usually the sensor 1 is mounted where the sensor two was mounted and sensor two requires a new bung installed after the cat. You have eliminated the warm up cat, assuming that you used the NISMO header.

That will throw off your sensor 1 STFT. Add to that that the connector for the sensor is in a bad place and tends to get full of water and has to be frequently dried out or you get bad readings. You also have to make an extension harness for sensor 2.

Hi Keith,

I have the 2J Street Spec Spyder header. I did verify with the manufacturer of the header the correct placement for the oxygen sensor 1 (top bung). I just left O2 sensor 2 alone - I was told readings from 02 sensor 2 do not affect engine performance (I do not currently have any engine codes)?

Thank you

Hi all, I tried a friends scanner, and it did pick up a LTFT that hovered around +5.5%. I then tried my scanner again, and it also picked up a fluctuating LTFT value that seemed to hover around +5.5%! Not sure what was going on there, perhaps simply a loose connection?

Well, I found a small hairline crack on my air inbox, I’m going to try sealing it with some self-sealing silicone tape and see if any changes register.

If you recently erased fault codes the monitors were cleared at the same time. The oxygen sensor monitor or catalyst monitor might need to be completed before long term fuel trim is updated.

Make sure whatever you seal the airbox with is labeled “sensor safe”.
For instance, fumes from household silicone caulk can damage O2 sensors.

I’m not familiar with that header, does it have a warm up cat (precat)? The one I’m familiar with does not have the warm up cat so the O2 sensors have to be moved. Edit: your header is not in their catalog anymore, but it is listed on Amazon, but no picture or specifications.

Hi Keith, it does not have a warm up cat, but the stock manifold does. I found a picture on insta of the header.

I have the O2 sensor on the upper bung as specified by the manufacturer.

Thanks,