New and Trying to Figure out What my Problem is

I am not a tuner and could use some help. I took the EFI tunning courses on here to help me understand data logs and speak the language, but I don’t have any actual tuning experience and could use some help figuring out what my problem is.

I’m running a 2011 Subaru STI as a track car. It was professionally retuned in the spring due to some knock issues that were assessed to be from heat soak. The temperature sensor was relocated from the MAF to the intercooler just prior to the throttle body (still running TMIC). The retune seems to have solved my knock issue during open loop and most the time on track, but I had a -4.2 Feed Back Knock show up on my track day yesterday at partial throttle.

-The car was tuned on 91 OCT (US California) fuel

-The car was running 93 Octane fuel on the east cost during this data log

-Motor is IAG short block with all the bolt ons, 1000cc injectors, AEM fuel pump, Blouch Dom 1.5 XTR turbo, etc

-After the Knock incident i topped the car off with 100 Octane (50/50 mix) and the issue did not occur again other than the occasional -1.4 Feedback knock under similar conditions.

It seems like there must be something going on if I’m having to run a 50/50 100/93 octane mix on a 91 tune to keep from having significant knock at the track. Data log is attached; the event starts at colum 775. Thanks for any help or insight you can offer.

Jake,

I'm not sure what happened but the forum ate my longer post, so here's the short version retyped.

If the car ran properly on this tune for a while and now is not, I'd focus on vehicle diagnosis.

You're 1-2 psi overboosting and staying over targets not just blipping over.

The engine is at 12.6-12.8 AFR on a target of 10.8-11.0 on low quality pump gas, so either the sensor is damaged and very wrong, you have exhaust leak, or major loss of fuel pressure or some other issue is actually making it run extremely dangerously lean for that setup and fuel.

The engine is misfiring sometimes at WOT over 5500 RPM.

The major knock event you mentioned shows AFR 15.6 at just over the threshold of boost which could certainly cause that, but figure out if the sensor is lying to you or not first.

Mike,

Thanks for the reply! I was just digging through logs from previous track days and noticed the discrepancy between the Sensor AFR and target AFR. Over the last three track days the difference has gotten progressively worse.

A couple things that happened since the retune in the spring: while having the trans rebuilt, the guys found a small fuel leak and an exhaust leak between the exit of the down pipe and cat back. The fuel leak was from one of the Cobb fittings below the TMIC, which they replaced with an ANS fitting (doesn't seem like this would cause a change in fueling) and they replaced the gasket/fitting between the downpipe exit and cat back. If the exhaust leak post downpipes existed at the time of the retune, do you think this could cause the issue? Seems like it shouldn't based on the location.

I'll start with swapping or testing the AFR sensor and see what kind of readings I'm getting. Thank you again for the help!

Mike,

Attached is a data log right after the car was pro tuned. There is a 20psi and 22psi map pull. Another thing that caught my attention that is noticeably different from the previous data log of my track time this weekend is the the Wastegate duty cycle is lower from this weekend compared to when the car was tuned. Would this help narrow down the issue I'm having or is it ambiguous?

Jake,

Exhaust leaks can impact lambda readings, so yes that can impact the tuning process.

I wouldn't go into boost until all issues are diagnosed and resolved.

The ECU is attempting to stop the boost from going over target, but it's not succeeding despite WGDC dropping to near zero.

Either the WG is sprung to make 20 psi or perhaps there's an issue with the gate or vacuum hose. It doesn't look like a hose being off though because it's not out of control, it's just making over target by 1-2 psi.

Thanks Mike. I realized I’m a dummy and was reading the waste gate cycle as the opposite (I was thinking lower meant increasing pressure vice decreasing).

I tested my AFR sensor, and it appears to be in good working order. I did find a fuel leak the fuel line that connects to my drivers side fuel rail. I’m hoping this is the fix. It makes sense to me that if the fuel system isn’t maintaining the correct pressure that open loop would run lean, but then when the motor is closed loop it seems to be running close to the commanded AFR. Which would make sense that the ECU would compensate for the error it’s detecting in the discrepancy.

Either way, I have to fix the fuel leak. I’ll start there and see if that fixes the problem.

How were you able to identify the misfires on the data log? I haven’t popped any codes yet. Thanks again for your help and time!

Jake,

Fixing fuel leaks is certainly a step in the right direction. Good find.

Since you're chasing multiple issues already, it seems worth a pressure and smoke test of your intake system at 25 psi based on your boost level. That will check the spacer gaskets I see in that pic which are prone to leaking.

I can't explain how I see misfiring without stepping on your tuners toes which I'm careful to avoid, but currently there are some known mechanical concerns, potentially others, and once the car is 100% perfect then hopefully all issues will be gone anyway.

Found a couple bolts that backed off my turbo to down pipe connection causing an exhaust leak while inspecting the car. I fixed the exhaust leak and fixed the fuel leak and just took the car out for a couple pulls. Sad news is it didn't fix my issue of the car running lean in open loop. I must have another problem. I was on the street, so limited in the pulls I could do but there is one in row 2420-2445. The curious thing is at first the hits close to target AFR, but then creeps back up to around 12.3. The car didn't do that in the other data log, but it might just be a fluke. I'm going to smoke test the intake track next, problem is I have a cheap smoke machine, so I won't be able to pressurize the system to 25 psi, but I'll see if it turns anything up and go from there.

Smoke tested the intake and there were no leaks. My tester can only do 15 psi. I’ll look at getting a better system that can do 25 psi, but I’m starting to talk myself into a fueling problem. If I had a leak in the intake system I would think my fuel trims would be significantly off. I ordered a fuel pressure gauge to test the fuel system, but I’m starting to wonder if I have a fuel pump or injector problem. Please let me know if I’m completely off on my logic.

Datalogging fuel pressure via a sensor would be a great step in narrowing things down, and a good tool to have for the future.

Looks like this issue is fixed! And I'm embarrassed to say it ended up being the O2 Sensor (insert face palm). I tested it with a multi meter at the beginning of my trouble shooting and it tested good. I had a spare O2 sensor laying around that tested the same as the sensor in the car, so I figured the O2 sensor was not the issue. I should have just swapped them out to start with, but I guess it's a blessing in disguise as the whole incident led me to finding the fuel leak and exhaust leak. I replaced the fuel pump and filter since that was a cheap TS step, but it didn't help. Then I figured I'd try the other O2 sensor out before I went further down the rabbit hole. Attached is my data log from a quick drive post the O2 swap (pulls are at row 449-494, 834-869, and 1670). The car holds 11.14 A/F Ratio in open loop under WOT now. Over boost is no longer an issue either. I'll take it to the track this weekend and see how it does.

It all sounds like progress. Good work sticking with it!