Hi

I had similar post few months ago, but I did not have all information.

Since I have the car, I feel it is not running with full power. When I disconnected the battery, the car was running perfect. Just after I bought it, I did some maintenance things:

spark plugs are new, engine oils, filters - everything is new
One time I cleaned MAF sensors and after that it was ok again, so I though that MAF was a reason, but unfortunately it wasn't.

I talked to one mechanics and he suggested to check the Fuel Trims.
He also told me, that Long-term Fuel Trims are cleaned, when the MAF is disconnected.

So I started driving with OBD2 Car Scanner (on Android) and I saw that
- Long term Fuel Trims - first is between 0 and 8%, second is between 0 and 2.
- Short Fuel Trims - first -10 to 5, second -15 to 2

So i disconnected MAF sensors, started the car, then connected and that resetted Long term Fuel Trims, so now I have

- Long term - both 0
- Short term - first: between -20 and 25, second between -20 and 25

Generally, when the Long term is 0, car is running fine!

As I checked, both MAFs have the same values whole the time (0,02 differences between 1st and 2nd).
Oxygen sensors are also changing.
catalysts are new
exhaust looks fine

Any suggestions would be appreciated

Have any trouble codes set in the OBD2? Fuel trims look healthy at a first glance - at least when you had the MAF plugged in. I believe with maf unplugged car is NOT in closed loop fueling, and fuel trims are irrelevant. How does the engine run in this state?
Monitor the reading for both banks on live data. Take the car for a test drive for long and short term fuel trims while idling and while cruising. Anything larger than +/-10% on the LTFT can be cause for concern.
Do a wide open throttle pull and record Load % and upstream o2 voltage (A/F sensor ?)

Those STFT readings are very low, which means the ECM is having to subtract fuel because the A/F's are indicating a rich mixture. The max is -25%, so the mixture (at 0%) has to be way rich for the ECM to be dialing so far negative. Did you change injectors on it, and are they the right ones?

I did more tests today, below are results.
However I do not see any abnormalities, MAFs are working the same, Oxygen sensors as well. I think I need to go to specialist with this.

Generally engine is running fine, but in low RPMs I do not feel the power, or maybe "I don't feel the torque". After reset - it is running perfect.
I did not you change injectors.

There are a very limited number of things which can make the alpha shift negative. Have the A/F sensors been changed, and are those right? The ECM adjusts fuel trim by way of feedback from the A/F's, so if those are falsely indicating rich, the ECM will incorrectly adjust lean. Yours are supposed to be 2.2V types, the 1.5V versions need a stronger resistor in the ECM and will read constantly rich (about 13:1 instead 14.7:1) if installed on a 2.2V engine. The only other reasonable suspects are 1) high fuel pressure, or 2) miscalibrated MAFs which are overestimating the incoming air.

I did not change A/F sensors, I have this car since 1 year only. It has 250k km (155k miles) and I think they are oryginal.
Any way to check A/F sensors? As I see someone recommended the "ECU reset procedure", but I did it 1 year ago and I saw no differences.

Thanks for uploading the data snapshots. I'm seeing the "F/T" values which are all flat lined at -20%. Not really making sense to me. Does your scanner have a LTFT1 and LTFT2 PIDs available?

VStar650CL wrote: ↑

Sat Mar 04, 2023 7:41 pm

Those STFT readings are very low, which means the ECM is having to subtract fuel because the A/F's are indicating a rich mixture. The max is -25%, so the mixture (at 0%) has to be way rich for the ECM to be dialing so far negative. Did you change injectors on it, and are they the right ones?

Is it true that unplugging the MAF will reset the LTFT to 0 but allow the short term to have feedback? Does the ECM do this calculation purely with O2/RPM/MAP inputs?
Also would not an oscillation between -25% and +25% give a median of 0%?

The A/F's don't oscillate like the rear O2's, they're wideband. You'll see some swing but it's very tiny, and the ECM is actually inducing it to make the rears swing and check the health of the cats. Sitting at idle, the fronts will look flatline a bit below the nominal 2.2V. Unplugging the MAF does zero-out the LTFT, but doesn't affect STFT. The latter is purely a product of how much metered air comes in and what mixture the A/F's indicate coming out, which is what "closed loop" operation means. "Open loop" means the ECM is using calculated values and not paying attention to the A/F's to verify the burn. The ECM knows that in a perfect world, X amount of air plus Y amount of fuel should result in a stoichiometric burn. In closed loop, the A/F's tell it how far from perfect the actual burn is, and the ECM adjusts the injector pulse widths shorter or longer accordingly in order to reach stoichiometry. LTFT is an accumulation of learned STFT's which tell the ECM whether the bank generally runs lean or rich, so you can think of it as a "permanent offset" applied to the injector pulse before STFT is calculated (and it's also applied in both open and closed loop). So in closed loop, the sum of STFT+LTFT tells you how rich or lean a given bank is running from moment to moment. Say an engine is running -10% LTFT and -5% STFT, after you pop the MAF's and clear LTFT, the same engine will show 0% LTFT and -15% STFT under identical run conditions.

VStar650CL wrote: ↑

Sun Mar 05, 2023 12:48 pm

Unplugging the MAF does zero-out the LTFT, but doesn't affect STFT. The latter is purely a product of how much metered air comes in and what mixture the A/F's indicate coming out, which is what "closed loop" operation means. "Open loop" means the ECM is using calculated values and not paying attention to the A/F's to verify the burn.

How is the ECM in closed loop operation with no intake air meter?

It isn't, certain DTC's just clear out its LTFT memory when you run it without a MAF.

Still confused but thanks for the tip vstar.
OP: It looks like the system is spiking rich intermittently. Driving STFT into the negative.
Something looks funky. What was the engine doing when the A/F spiked around 14:48:00 in the waveforms?

fontana dan wrote: ↑

Sun Mar 05, 2023 2:18 pm

What was the engine doing when the A/F spiked around 14:48:00 in the waveforms?

Looking at the throttle, I think I just parked in the parking at that time

KarolGT wrote: ↑

Sun Mar 05, 2023 2:48 pm

Looking at the throttle, I think I just parked in the parking at that time

It seems to have some correlation with throttle input then. You said it feels like the car loses power at low rpm? Is it when you step on it, or when you are gentle on the gas?
Would help If you can do another road test and use the blue app to record a WOT pull or at least a snap throttle rev. Hammer on it some and record the same line graphs.

When you "blip" the throttle, wideband sensors behave like the image below. They go very rich (lower voltage) during the RPM rise and then rebound lean (higher voltage) when the accelerator is dropped. When there's no action on the throttle they should be more or less flatlined, usually a tad rich from stoichiometry because a slightly rich mixture improves the idle. For 2.2V sensors, 2.15V is probably typical at idle.

Yes, car has no power at low rpm, when it start accelerating, from around 4-5k rpms is running fine, so basically yes, the throttle respond time is very low. It is much better on SPORT, but on NORMAL has big delay. Of course after ECU reset (battery disconnect) it is ok.

If I remember correctly, there are 2 gas pedal sensors and both are showing the same values.

Can you recommend some app (for Android)? I have BT OBD2 so I can record whatever is needed for this.

VStar650CL wrote: ↑

Sun Mar 05, 2023 8:40 am

Yours are supposed to be 2.2V types, the 1.5V versions need a stronger resistor in the ECM

How to check if my engine needs 2.2V or 1.5V?
I only found this part number: 22680-7S000
but there is no iformation about the voltage.

That will be in the FSM, assuming your ride is the same as a USDM model. Usually you'll find a chart with each section for A/F sensor DTC's, like P0130/P0150. See EC-237 here, the USDM's use a 2.2V:
https://www.nicoclub.com/service-manual ... 0%2FEC.pdf