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13 Subaru Forester 2.5L Non-Turbo = Burning up catalytic converters

  • jhonda
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05 May 2019 20:12 #29323 by jhonda
Hi there, I am having a lot of trouble diagnosing this Subaru. It all started with clogged cats to where the vehicle would not start, the dealer diagnosed that it needed new cats - customer brought the car to us to install the new cats, which we did.. car ran fine for about 2 weeks, car comes back with a stalling issue and a rotten egg smell and P0300. At this point, I believe I have gone through every system starting with fuel trims. Fuel trims are within spec at idle and car commands to pull fuel at 3000 RPMs. From manufacturers specs we have a high injector pulse command, the car runs anywhere from 3.7 to 4 MV . we have tried to add additional fuel, we have created vaccuum leaks to try to make the engine run better but it stays exactly the same. We have went over mass airflow data, everything appears to be fine. We have compared map sensor to MAF bariometric pressure, everything appears to be fine. Our O2 sensors have activity. We checked compression, weve checked timing via data pids, verified that all coils are firing, we put new spark plugs, just because. I tried to correlate crank sensor pulls with # 1 coil fire via scope but couldnt get a comfirmative reading, i believe i was doing something wrong. We hooked fuel pressure gage up, pressure is fine and we fired each injector individually to monitor spray pattern, everything is equal. If you have any input or need any other info, please ask I really need help, I sat on the phone for hours with two different techs from identifix and no one could seem to come up with a conclusion. Thanks

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  • Tyler
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06 May 2019 09:10 #29329 by Tyler
Hey jhonda! Do you have any data or screenshots you could post that were taken during the driveability issue? Specific trim values at various loads would be helpful. Can you reproduce the P0300 or stalling symptom?

Fuel trims are within spec at idle and car commands to pull fuel at 3000 RPMs.


Do you mean that the trims start to go positive? Or negative?

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06 May 2019 12:55 #29342 by Dtnel
I'm still learning this stuff but I am curious on this does this do it when the car is warmer versus being cold, little symptoms like that do they make a difference?

If I'm understanding this correctly it sounds like there's too much fuel getting in there. From a learning perspective am I making a good assumption based on what you're saying or not? I don't mind constructive criticism because it makes me better at what I do as well. Some of you guys are experts some of you guys are novice and some of you guys are beginners I think I'm between beginner and novice then I'm always shooting the try for the Moon because I like big challenges

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07 May 2019 12:19 #29363 by Tyler

Dtnel wrote: ...then I'm always shooting the try for the Moon because I like big challenges


YES. :woohoo: I love it!

From what jhonda posted, it would seem that there's a (perceived) lean condition, as the PCM is increasing the injector pulse width. Is it a real lean condition? And if so, when? Is it a false lean condition?

I sat on the phone for hours with two different techs from identifix and no one could seem to come up with a conclusion.


I'm genuinely puzzled by this. :huh: Did they not have any suggestions for you, as far as what direction to take your testing? Speculation?

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09 May 2019 12:11 #29444 by jhonda
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09 May 2019 21:21 #29457 by guafa
Hi everybody,

Have you compared calc. Load in screenshots #1 & #2?

That only make sense if jhonda took #1 when deceleration. Did you?

At idle calc. Load is 24.7% but at 3196 rpm is 20.8%

Note also screenshots #3 & #4

Injection pulse is wider at idle than at 3156 rpm

I think would be better a video. So that we can see lots of data.

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