Can anybody explain why my STFT & LTFT take a dump randomly?

[Jesse36m3]

I'll be cruising perfectly fine, monitoring a good AFR, then all of a sudden the car dumps fuel, AFR drops to 11.02, which is max on the stock sensor, and I can barely accelerate without sputtering and bogging. Eventually it will clear up, then go right back to taking a massive dump until I reach my destination and let the car relax for a couple hours.. then it will be fine when I start it up. After studying the log, I can confirm that a super negative STFT correlates with an extremely rich mixture.


Datazap Log


Some background:
- Car is an early 2013 with 82k miles. Drives perfectly fine otherwise - I've never had a single problem with it while N/A.
- JDL v2 turbo kit has been installed for roughly 11k miles. After pondering on this for months, I realized that this started happening after an intense track session in 90F weather over the past summer. (East coast).
- No codes, no knocking that I see, no boost leaks, no vacuum leaks, no crappy eBay parts anywhere, all new gaskets and hardware everywhere, I have an oil cooler, keep up with a 3-5k oil change interval, clamped all suggested hoses under manifold, religiously use premium 93 octane gas, installed a nice AOS system, tuned with a nice boost controller, heatwrapped and ceramic coated everything, no abnormal sounds anywhere - sounds exactly like it did when stock with the exception of an UEL exhaust note, etc etc. I really spared no expense on this car because I wanted it to be "reliable."


I assume most of you will come to an early conclusion and blame the tune, however, I did not experience this while tuning. This sort of developed over time which leads me to believe it could be an electro/mechanical issue.


My plan is to just go ahead and replace all the spark plugs, even though they were changed at 60k, along with the coil packs. I've read that extreme heat can prematurely kill them (track). While I'm in there I'm going to give it a compression test and I may [more than likely will] replace the DI seals.


When it's running right, she PULLS. I would just like some guidance or suggestions before I start throwing money at other areas that I shouldn't even be looking at. It's just extremely frustrating to try and track an intermittent issue and I refuse to take it anywhere for that very reason.


Any help would be appreciated!

[Kiske]

I cant check the logs atm but, your thoughts makes me think a boost leak. A minor one opening and dropping air after the maf.

[Kodename47]

Well you're way too rich all the time in closed loop, hence the really high negative trims. Either the tune is off, you have a leak post MAF or dodgy injector. Or the O2 sensor could be shot due to running rich all the time.

[steve99]

looking at the pi and DI injector open times it appear the ecu is asking for a lot of fuel. you have not logged commanded AFR.


also are you port injectors stock ?? as if they are bigger injectors its asking for huge amounts of fuel. Maybe injectors not scaled or tune is targeting very rich afr.

[gtengr]

+1 for air leak. On my car with a supercharger this same issue has been related to a post-MAF vacuum leak. Check and make sure all clamps are fully seated onto the piping and not crushing down on the edge and making the pipe end into a D shape. Since it runs correctly some of the time, I'm guessing your hardware is probably good.

[Jesse36m3]

Originally Posted by Kiske

I cant check the logs atm but, your thoughts makes me think a boost leak. A minor one opening and dropping air after the maf.

Originally Posted by Kodename47

Well you're way too rich all the time in closed loop, hence the really high negative trims. Either the tune is off, you have a leak post MAF or dodgy injector. Or the O2 sensor could be shot due to running rich all the time.

Originally Posted by gtengr

+1 for air leak. On my car with a supercharger this same issue has been related to a post-MAF vacuum leak. Check and make sure all clamps are fully seated onto the piping and not crushing down on the edge and making the pipe end into a D shape. Since it runs correctly some of the time, I'm guessing your hardware is probably good.

I'll be damned if it's only an air leak. I swore up and down it was good but you guys may be right. I'm going to check all the connections again when I have it apart next to do the plugs.

Originally Posted by steve99

looking at the pi and DI injector open times it appear the ecu is asking for a lot of fuel. you have not logged commanded AFR.


also are you port injectors stock ?? as if they are bigger injectors its asking for huge amounts of fuel. Maybe injectors not scaled or tune is targeting very rich afr.

I knew for sure there would be something I missed to log
Injectors are stock. Literally the entire engine is stock.

[steve99]

Check the manifold pressure at idle should be abput 0.4 bar with engine rinnng at idle and 1 nar with engine stopped

[Jesse36m3]

I don't want to speak too soon, but I just wanted to update this thread to say that replacing the coil packs and spark plugs seem to have fixed the issue. I am leaning more towards a bad coil packs being the culprit. The spark plugs weren't in the best shape [little wet] but I've definitely seen worse. They were also a little burnt at the base of the ceramic which may be indicative of overheating at some point.



Coil packs were original 82k OEM, and I replaced the plugs around 55k miles - 11k turbo so far with 8 track days last year seemed to have killed them nice and early.

[D-VO]

Huh...Really? I'm having the same weirdness and I've already replaced all 4 coils. I read over on a Ford website that says its normal for the STFT to raise when rolling in neutral. Something about the incoming air being higher than expected when at idle.

[jflogerzi]

I would say a bad o2 sensor.

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