Fuel trim help

[Bry1234]

Hello all, nissan 06 xtrail 2.5l. Trying to figure out a issue with these fuel trims at idle.
Ltft -10%Stft +8 to+13% with a short blip every 10 or so seconds of -100%. Upstream 02 sensor oscillates but hangs out more in low voltages even going below .1 volt to .04 volts. Thoughts?
Symptoms are hard start when cold- 20 and pinging from engine when cold while driving until it warms up a little.

 

[Astro14]

Sounds like a vacuum leak. Check for broken/brittle hoses and connections.

 

[Bry1234]

Yes I have checked everywhere for vacuum, is it possibly a lazy 02 sensor?

 

[mk378]

Starting and cold running are open loop. I'd start with checking the live data IAT and ECT sensors cold before starting, they should read close to ambient temperature.

 

[chemman]

Check to see if your emissions system charcoal canister is contaminated with liquid gasoline. Another way to test for this is to disconnect the EVAP purge valve and see if the periodic swings towards -100 % stop. Yes, your check engine light will illuminate and a DTC will be set, but it is an easy test to do.

 

[Bry1234]

Starting and cold running are open loop. I'd start with checking the live data IAT and ECT sensors cold before starting, they should read close to ambient temperature.

Maf and ect sensors are good and reading correct data.

 

[Bry1234]

Maf and ect sensors are good and reading correct data.

Sorry guys, stft is at -10% and no more blips going - 100% also downstream 02 sensor is fluctuating as well although I swear the stft was positive yesterday, only thing I did was take out pcv and clean it. And check gap of plugs which were off . Changed gap from .47 to .44

 

[bbhero]

Sounds like a vacuum leak. Check for broken/brittle hoses and connections.

I think this could well be right.

My Nissan Altima VQ had LTFTs high as 15 and STFT were running 25 percent to 10 percent. Ended up being a vacuum leak and a bad throttle body.

 

[SC Maintenance]

Hard start likley has nothing to do with LTFT or STFT - because cold start is in open loop mode - so fuel trims aren't even in play.

LTFT should be +/-5%. However you won't throw a code until 20 or 25% - I forget which, so 10% isn't terrible for an 18 year old car. STFT are more or less meaningless for diagnostics. If your STFT is running constantly one way or the other it will simply adjust the LTFT over time.

Lets start with your reading LTFT with the engine fully warmed and driving a constant speed - correct? Its not unusual for them to float around a few % points even on a short trip.

-10% means the ECU is taking away 10% of the fuel compared to spec at that load. So its actually running rich - unlikely a vacuum leak. Could be dirty MAF sensor, or bad primary 02 sensor, or possibly bad plug (s) giving you the slightly rich condition. Not sure if any of those are contributing to your hard start.

Have you tried a cold start with starting fluid - just for funzies. If it fires up immediately on starting fluid you can assume your issue is fuel related, not ignition / spark. If no change, then it likely is not fuel.

 

[Bry1234]

Hard start likley has nothing to do with LTFT or STFT - because cold start is in open loop mode - so fuel trims aren't even in play.

LTFT should be +/-5%. However you won't throw a code until 20 or 25% - I forget which, so 10% isn't terrible for an 18 year old car. STFT are more or less meaningless for diagnostics. If your STFT is running constantly one way or the other it will simply adjust the LTFT over time.

Lets start with your reading LTFT with the engine fully warmed and driving a constant speed - correct? Its not unusual for them to float around a few % points even on a short trip.

-10% means the ECU is taking away 10% of the fuel compared to spec at that load. So its actually running rich - unlikely a vacuum leak. Could be dirty MAF sensor, or bad primary 02 sensor, or possibly bad plug (s) giving you the slightly rich condition. Not sure if any of those are contributing to your hard start.

Have you tried a cold start with starting fluid - just for funzies. If it fires up immediately on starting fluid you can assume your issue is fuel related, not ignition / spark. If no change, then it likely is not fuel.

New maf and plugs, so new 02sensor comes wed.

 

[fitrucker]

LTFT is applied to startup maps and all open loop operations. The short term is positive to get LTFT closer to zero. It trying to correct a problem. Could be a lot of things including a dirty fuel injector. Bad battery,Bad fuel, temperature changes but usually correct in a cycle. Spark plugs good but I would not change sensors with out a code or testing them with a scanner. -10 is not too bad but the jumping to 100 percent leads me to O2 sensor. O2 is nothing more than a air meter in the exhaust. Correcting fuel.

 

[LvR]

Hello all, nissan 06 xtrail 2.5l. Trying to figure out a issue with these fuel trims at idle.
Ltft -10%Stft +8 to+13% with a short blip every 10 or so seconds of -100%. Upstream 02 sensor oscillates but hangs out more in low voltages even going below .1 volt to .04 volts. Thoughts?
Symptoms are hard start when cold- 20 and pinging from engine when cold while driving until it warms up a little.

vs

Sorry guys, stft is at -10% and no more blips going - 100% also downstream 02 sensor is fluctuating as well although I swear the stft was positive yesterday, only thing I did was take out pcv and clean it. And check gap of plugs which were off . Changed gap from .47 to .44

Can we get actual proper figures for LTFT and STFT variations seen about 1 minute after starting the engine and without touching the throttle please - the above difference is quite confusing.

In fact - post a graph of your O2 sensor voltage

 

[zray1]

Likely nothing to do with the OP’s issue, and totally anecdotal: I added too much Techron Full Fuel System Cleaner during my last fill up. Like double the recommended amount of 1 oz per gallon.

The trim numbers went from -1 to 0 to -6 to -8. As soon as the fuel level was down to 1/4 tank (20 gallons being full capacity) I filled up again. After a few miles the trim numbers went back to -1 to 0.

What does all that prove ? Haven’t the foggiest notion.

Z

 

[LvR]

Likely nothing to do with the OP’s issue, and totally anecdotal: I added too much Techron Full Fuel System Cleaner during my last fill up. Like double the recommended amount of 1 oz per gallon.

The trim numbers went from -1 to 0 to -6 to -8. As soon as the fuel level was down to 1/4 tank (20 gallons being full capacity) I filled up again. After a few miles the trim numbers went back to -1 to 0.

What does all that prove ? Haven’t the foggiest notion.

Z

I reckon it proves your fuel system is working well in closed-loop mode and is quite able to counter your insistence on screwing with its head

 

[Bry1234]

Im unable to record, so as it stands, Ltft is -5% and stft is -12% at idle and at 1500 rpm’s ltft is 0 and stft is -18%. Upstream 02 sensor is oscillating normally from .03 volts to .88 I put a new one in, and down stream 02sensor is at 0.16volts constant.

 

[fitrucker]

No codes? That is better. Might have a air leak. I would say clear the codes even if none to see what happens with a full tank. My fuel trims are negative 5 long fuel trim and plus or minus 5 short term at idle. Clearing the codes erase learned behavior but also could make a problem if a sensor is out, but then you know where to look.

 

[Bry1234]

No codes to clear, I have reset the fuel trims, and a idle volume relearn for throttle body as well.

 

[incognito_2u]

Hello all, nissan 06 xtrail 2.5l. Trying to figure out a issue with these fuel trims at idle.
Ltft -10%Stft +8 to+13% with a short blip every 10 or so seconds of -100%. Upstream 02 sensor oscillates but hangs out more in low voltages even going below .1 volt to .04 volts. Thoughts?
Symptoms are hard start when cold- 20 and pinging from engine when cold while driving until it warms up a little.

These numbers are very “Toyota-ish” in the sense that I was getting similar data that pointed to a vacuum leak (the dreaded intake manifold) On the 2006 in my sig. Appeared when the weather got colder.
Any codes thrown?

 

[Bry1234]

No codes to clear, I have reset the fuel trims, and a idle volume relearn for throttle body as well.

If it’s an air leak, I certainly can’t find it. The intake on these is hard to do a leak test without a smoke machine

 

[incognito_2u]

If it’s an air leak, I certainly can’t find it. The intake on these is hard to do a leak test without a smoke machine

Get yourself a can of carb cleaner and as the engine is idling, spray the cleaner in and around the area of the intake manifold gasket. Any change in idle usually confirms your issue.