Help with hesitation issue
 

Hey guys! I have a track day coming up on the 30th and an issue popped up I need help with asap. The car has been running the same tune for a year and a half now and its been great. Was just working on hood vents when this started, most likely a coincidence.

Under light throttle and low rpms (under 4k), the car is hesitating pretty hard. Kind of jerking/bucking back and forth. Seems to be worse under more load like going up an incline. It seems to be intermittent too, happened two nights ago, couldnt get it to replicate yesterday morning, but then in the evening I was able to capture it in a log.

The log is just me going through gears 1-5 up a gradual hill. I can see in the log where I'm feeling the issue but I'm not sure how to diagnose anything, the rpm's jump back and forth when I'm accelerating. I popped the hood and dont see any loose hoses or connections. Could you please take a look at my data and let me know if anything stands out to you?

Only 36k miles so hoping its not spark plugs

Here's the datazap: https://datazap.me/u/motox16/815-issue?log=0&data=30

Thanks for any help!

I see a couple misfires occurring right in the spot of RPM fluctuation on cylinders 2 and 3. Your throttle angle is all over the place in these regions of fluctuation with drops in torque demand and various other parameters. I have very little experience in understanding and diagnosing from data logs. But maybe there's something up with the TB or MAF sensor needs cleaning? Maybe an issue with the injectors?

Check your O2 sensor. Your AFR is all over the place.

What can I check for? Its tight, can I clean it? Its the wideband sensor that came with the AEM gauge

I noticed the throttle angle as well, not sure if its just my foot moving with the car jerking back and forth :iono:

I'll try cleaning the MAF and I might pull my injectors out to get cleaned, I did pick those up used but they've been working fine for a little over a year

Thanks!

Doubt it's your foot. Short term fuel trims are up and down as well, so fueling increasing and decreasing right in that region. Again, I'm not sure how it all works. But the fuel system isn't giving you smooth values and the mass air flow is showing a fluctuation in the air coming in as well, thus throwing off your AFR. This is why I'm wondering if something is up with the TB, but I don't think I've heard many cases of TB's failing. You are running ethanol, and if you got used injectors, the question would be how used. Would definitely be nice to get them cleaned and resealed considering your mileage. But that depends on how used these injectors were, did you get them cleaned prior to installing them? When were they installed? Were seals replaced?

EDIT: As mentioned above, O2 is a possibility. Don't know why it would work most of the time but be limited to working properly in a certain RPM range though?

The injectors were installed two years ago, seals were replaced but they were never cleaned. Not sure how used they were but I think the guy before me had been running them for a year or two, I got pretty much my whole turbo setup from him

Well if seals were replaced, then they wouldn't need to be cleaned as they would be new? And if that's the case, I wouldn't think the injectors to be the problem so quickly.

I guess just the outer orings were replaced, nothing internal

What makes me question the O2 is not where it is breaking up, but in the area where it looks like you are in between 4th and 5th gear where it is pretty steady RPM. AFR is all over there too.


Found this on supra forum for testing an AEM wideband. Use at own risk.

To test the gauge to see if it is working correctly:
Unplug the sensor at the lock connector. Turn iIGN on but don't start the car. Gauge defaults to 14.7(8) in test mode. Measure the voltage on the white wire (output) to ground. It should be around 2.375 VDC. If this is the case then your gauge is working correctly. It should be noted that I am in the P0 mode (for gasoline/AFR readings).

To test the sensor:
Take sensor out of downpipe and lay on top of cold engine (sensor should be plugged back in at this point). Turn on IGN but don't start the car. After a few seconds, your gauge should read maximum lean condition (>18 or --- on the scale).
Next test for richness calibration. Put some acetone in a rag and put sensor tip on this. Don't immerse sensor tip in the acetone, just set it on the saturated rag. Turn on IGN but don't start the car. After a few seconds, the heated tip of the sensor will start to evaporate the acetone and you should get a maximum rich reading on your gauge (<10 or ---).

If all the above test pass, then you have either a wiring problem or another possible mechanical issue.

Looking at some of my older logs, my afr has always bounced around like that. +/-1 of target has been pretty typical. My car was a little difficult when tuning and that fluctuation is something James and I struggled with

Here's one for reference: https://datazap.me/u/motox16/427-cruise?log=0&data=30

I will try that out though, seems like an easy enough test to eliminate a possible issue. Thanks!

Ok I dropped my injectors off to get cleaned, should have them back in a day. One thing I did notice in the log is that when its breaking up my port injection % jumps all over the place. Not sure if that means anything but the sheathing around one of my injector wires had started to get gummy/was sticking to the rail cover and looked a little melted. Might pull that back and make sure the wires are good underneath

Ok I got the injectors cleaned and tested, their flow rates and patterns looked good, one connector was broken so replaced them all but sadly no improvement. Also cleaned the maf with crc maf cleaner and no improvement either.

I actually started having some issues present themselves during startup, car almost stalls. Captured it in a log here: https://datazap.me/u/motox16/817-iss...?log=0&data=30

Why are my maf and rpm lines invers? Seems like they should move in the same direction...:bonk:

This goes back to me still leaning on something wrong with the air intake side. STFT is still bouncing there too, you're running real rich when RPM gets up. Seems like when you spike in RPM during idle, it tries to compensate and raise the air flow and lower the fuel to get back to a proper AFR. O2 sensor can still be a problem for sure and should be at the top of your list to replace or check next as it can have directly affect the AFR adjustments the car is trying to make. Maybe your MAF sensor is just going faulty and needs replacing?

Also (still unlikely but) wondering about that TB and whether everything is ok there. I mentioned earlier I am not familiar with any TB problems on this platform that people have talked about, but I have had a TB go bad on another vehicle in the past - and these are the kind of symptoms I experienced, but it got much worse quickly in my case to the point where the car would go in limp mode.