I'm doing some research and collecting data while I let this thread gather input...

This has just started today, my car is lightly stumbling at highway rpms. I open up torque and check the data. First thing I notice is that the long term fuel trim is at 0% even though I didn't reset the ECU. So I check the readiness codes and both the catalyst and o2 sensors are incomplete. I'm waiting for a CEL once the 2nd wave of readiness codes goes through.

So the LTFT is low. Its typically at -5.5% but after driving around in a combo of city and highway its only at -.8%. On top of that I check the STFT and its looking weird. Im seeing spikes as high as +43%. At idle I watch as the STFT slowly climbs from +10, 20, 30, 40% with each reading of the app.

I get the car home, let it run and pop the hood. Nothing appears wrong, no disconnected hoses. I see no abnormalities in the timing advance, idle rpm, coolant temp. The car idles a little rough but thats normal.

I rev the engine up to 2500 and check both o2 sensor readings. Neither of them move by more than .5 volts, the upstream is reading around .1 volts and the downstream is .8 volts. When I was driving I would see some activity from the sensors but now I see almost none. The ECU says its in closed loop though.

I've replaced both these sensors within the past two years. But what I'm stumped by is that both sensors are acting funny.

So recap:
Positive fuel trim, especially at idle
Lean exhaust (rich fuel adjustment)
Both o2 sensors acting funny
No apparent exhaust or vacuum leak
Stumbling at high rpm
loudly ticking fuel injectors (not valve ticking, this has been happening for a little over a month though)

I'm gonna do a fuel pressure check, vacuum gauge test and get some raw data posted but I wanna see if you guys have any ideas too.
Replace my o2 sensor is my initial thought but I wanna double check before doing it since its relatively new.

Thanks

 

Update:
Heres the data, the car was warm enough and went into closed loop. I let it idle a while then revved it to 2500. I then revved it higher. I saw nothing significant from the o2 sensors. The vacuum is reading low but I hooked my actual gauge up and it read 23 in/hg. I think torque is reading something wrong. On the screen it said the same too.

 

What is time step for each row of data?

What looks incorrect to me are:
>Primary O2 sensor (too high at first and too low for remaining time).
>STFT in first data group and 2nd data group looks too high.

LTFT (-0.78) looks OK.

Have you plotted these to understand trends? I know some Obd2 scanners are too slow to track fast changing items like primary O2 sensor and STFT. If this is case, you may be getting a false picture of trending.

Vacuum level doesn't change w/ rpm. It should go down (more negative) during rpm increase,...I think. I always get confused when discussing absolute and gauge vacuum pressure.

good luck

 

The data is all continuous. about 30 seconds of run time to maybe 3 or 4 minutes.

Ive been tracking my fuel trim for a while now and it should be -5.5% or at least close. This has remained true after 1k+ miles of travel in city/highway. This was all of a sudden that the fuel trim drops close to 0 and the engine starts to stumble on the highway.

I did a fuel pressure check but forgot to disconnect the regulator. But I did check the pressure with the rpms, it was 32psi, spiked to about 40 with a real quick rev but mostly stayed at 32 throughout the entire rpm range. Is my fuel pump finally kicking the bucket? I replaced my filter. i can do a voltage test on the fuel pump.

Whats strange is driving back I checked my readings and everything seemed a bit more normal. O2 sensor readings were reading a bit rich at idle and all around but my STFT was closer to negative at that point.

The data points recorded are sequenced to be as closely together as possible for each of those rows so i trust they correspond pretty accurately, I have been able to see graphed data in the app itself when I choose to, it just exports as excel data.

Vacuum readings are relative to STP so its reading 23 in/hg. An rpm increase when not under load will cause the vacuum to drop but then very quickly return to normal. So a steady 2500 rpm will read the same as 700 rpm if there is not change in engine load. When driving it drops. These points are all in neutral.

 

Heres the data from a trip to the auto store. Fuel trim starts to get closer to 'normal' but in my next trip it goes back to the issue. Its kinda intermittent but enough that I expect a CEL soon.
Symptoms say fuel pump but the data says both o2 sensors went bad at the same time. So either an electrical issue or the fuel pump is bad and the ecu is trying to enrich a lean fuel mix from a bad pump and causing odd o2 readings.
Im trying to solve this before something goes out and im stranded on the highway. The stumbling mostly happens when Im around 55 mph.

 

Your O2 sensors may be OK. You can't trend O2 sensors w/ such a coarse sampling interval (several seconds). Readings go from max to min several times per second at rpm's above idle.

Your secondary O2 sensor has readings that would appear erroneous; V > 1.0. It should be 0.9 or less.

Following link may be useful.

What are fuel trims all about?

good luck

 

I actually read that article yesterday. Ive been studying fuel trims since I started monitoring mine. Thats the odd thing I notice though is that when the voltages are above 1 volt it seems that the sensors aren't being read by the ECU and that would be why they are above 1.

I monitor them using a graph rather than numerical values, side by side. Somethings going on thats causing my fuel trim to go high. Especially at idle.

 

One thing I should mention is that the stumbling occurs when I decelerate from highway speeds. It happens if I ride the throttle a little- since the fuel injectors will cut off to save fuel when the throttle is closed but activate again as soon as the TPS and MAP sense a change. It should be a smoother transition rather than a failure to provide sufficient combustion when reactivated again.

MAP sensor
Fuel Pump
Fuel Injectors/Resistor

 

I over think things still :P

Someone suggested an exhaust leak test using seafoam. I always have that stuff around. I did it and saw my header leaking at the head. Its from a stripped bolt that for a while I had secured. Guess it came loose. Now I gotta look at a more permanent fix.

Thanks for your help texas.