FBO Coupe Breaks Up Around 3200RPM

NoKz

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Hey guys, I'm curious to see if anyone can lead me in right direction to continue diagnosing the issue with my 2018 Civic Si Coupe.

The specs are as follows:
  • PRL Cobra CAI w/Race MAF
  • PRL Catless Downpipe
  • PRL Frontpipe
  • KTuner Flex-Fuel Kit
  • E40 Fuel Blend (91 Oct & E85)
  • KTuner v1.2
  • TSP Stage 2 Tune
KTuner Log File:

Symptom(s): Car breaks up in gears 3-6 when over 3200 RPM and/or 30% throttle. After 20 or so minutes of highway driving, the issue appears to dissipate.

Description: When I start my car to drive it, I usually let the ECT warm up until about 170'ish degrees before driving off. I monitor this using TunerView on my head-unit. Once the vehicle is warmed up, I go about my drive. Primarily, the vehicle is used to get to work and back, which is roughly 62 miles round-trip.

When starting my commute, if I take 3rd gear over 3000-3400 RPMs it will break up like the vehicle is cutting ignition timing. If I push through it, the vehicle will go into limp mode and I have to restart it. If I let off, I can continue driving without issue. When going into limp mode, I get no check engine lights, no error codes, nothing.

After about 20 minutes of steady driving on the highway, the issue appears to go away. I can drop down to 3rd gear and rip on the car, but it will break up around 5K instead of 3K. Normal street driving is fine and I can rev beyond 3K without issues. But if I shut the car off and restart it, the issue comes back.

I actively monitor my Knock Control, Fuel Pressure Target, Fuel Pressure and AFR. My Knock Control is consistently at 0.49 on E40 and can go up to 0.54 when on 91 octane only. Previously, with different spark plugs, it would be all over the place. I replaced them with OEM spark plugs and it has been much more consistent.

I have been trying to diagnose this issue for a while, but have been unable to narrow down the root cause. I have done the following in attempt to try and diagnose/fix the issue.
  • New OEM Spark Plugs
  • Swapped Coil Packs w/Wife's Si (No Change)
  • Flashed to TSP Stage 1 Tune with 91 Octane
I've put a link to the KTuner log file when I flashed to the TSP Stage 1 Tune and it immediately broke up once I hit 3000 RPMs. If anyone could give me some insight, I'd greatly appreciate it. If not, she'll go back to stock and go to Honda for diagnosis. Thanks!
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gtman

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Can you upload a normal .kdlg file (in a .zip file) here? It's much easier to check out that way IMO.
 
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NoKz

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gtman

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No clue what a .kcl file is. My KTuner program doesn't recognize that as a Ktuner datalog.

Edit: you uploaded your TSP tune file. :eek:
 
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NoKz

NoKz

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No clue what a .kcl file is. My KTuner program doesn't recognize that as a Ktuner datalog.
Interesting, that's why my KTuner extracted it as. Let me see if I can try again.
 


gtman

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See my edited post above. (You may want to delete that TSP file from the forum btw).
 
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NoKz

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I would wager money on injectors.
That's what I've been leaning towards.I may swap injectors with my wife's Si to see what happens. Afterall, Honda has a known issue with them.
 

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I cant open log files at work. What do the trims look like?
 


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I cant open log files at work. What do the trims look like?
Here's a screenshot of the spreadsheet log. High-lighted is right when I let off the throttle.

Honda Civic 10th gen FBO Coupe Breaks Up Around 3200RPM BgfVuMu
 

gtman

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OK, here's the thing. I know a bit more than the some but I'm no pro. Here's a screenshot of a moment on the datalog. Your short term fuel trims were off quite a bit from time to time. I also wonder about the amount of misfire events. Of course it was only a 3 minute datalog. Hopefully our pros can chime in.

Honda Civic 10th gen FBO Coupe Breaks Up Around 3200RPM Capture
 
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OK, here's the thing. I know a bit more than the some but I'm no pro. Here's is a screenshot of a moment on the datalog. Your short term fuel trims were off quite a bit from time to time. I also wonder about the amount of misfire events. Of course it was only a 3 minute datalog. Hopefully our pros can chime in.

Capture.png
Good eye. I didn't know what to really look for. So it is looking like injectors then huh?
 

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More than likely. My s.trim was doing the same thing in my logs while driving especially at super light throttle. Very little throttle tip in at high vacuum. Thought it was something to do with rev hang/fuel overrun settings but always felt it was not right because it only happened toward the end of 20k miles. Turned out my injectors were progressively failing. There is a "reduction" that is applied normally in this area by the computer....when it cant reduce enough directly it has no choice once the rich mixture hits the o2s the trim will react. If you have access to try I would see if an induction service makes any improvement (i doubt it but would be something to try).


edit: actually my step one if it was my car would be straight 93 with a new tune file and see if there are any changes. ethanol can cause black goo/tar buildup in the tip of the injector with heavy use (sugar in the ethanol falls out of suspension at the tip of the injector when exposed to the heat allegedly). This is normally resolved as soon as pump gas is applied to this goo it usually dissolves. Like if you had an injector held in your hand that had this issue and dipped the tip in a small jar of 93 it would almost instantly dissolve to brand new condition....that's how "reactive" it is.
 
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gtman

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E85 seems to be a culprit in some of these injector issues, no?
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