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Hello everyone, I’m new to the forum and an aspiring advanced DIY’er. Admittedly I am a bit of an ex “parts changer” (don’t punch me in the throat) and I’m sick of that routine. Trying to be more practical and methodical in actually diagnosing a problem.
2001 Subaru Outback
5-speed Manual
2.5L 4cy non-turboLast week I had a P0171 (system lean) and before I had much knowledge at all around diagnosing this issue my first steps were vacuum leaks. There was an exhaust leak near the downstream O2, I have fixed that but not the issue. I pulled a lot of vacuum lines and can see no visible cracks/holes and I tested all over with propane. found nothing. Upon the vacuum line inspection the I noticed the PCV was functioning but was a bit gummed up and a little bit sticky, so I did replace that, and it was time for a new air filter anyway so it got one of those. for shits and giggles I pulled the battery to clear the code. The more I researched I realized this was all most likely not anything to do with the problem to begin with as my idle was very steady around 760RPM . I purchased a scanner over the weekend when I did all of this. For the last 3-4 days the check engine light has been gone and STFT have been running +/- 4 or 5% with a LTFT of about 7-8% at idle and around 13% under load. I knew some issue was still hanging out but the last few days I was not OVERLY concerned… On my drive into work this morning I was monitoring the live data on the scanner. There is now again a pending 0171 code, after roughly 300miles of driving. At Idle my STFT and LTFT are roughly the same but now under load they are screaming and seem to be maxing out. once I’m back to idle they level off and the ST is within acceptable range at 4-5% and the LT around 10%
Up until not the STFT had been fluctuating slightly + or – a few percent to almost 0% so I pretty much ruled out any problems with the 02’s. I’m not entirely sure what turn to take here but with my limited knowledge I know it could easily be a possibility I’m having fuel issues. the 01 outback seemed to have a MAP only (a possibly culprit?)
any help into some other testing and diagnostics I can do to help narrow this down would be greatly appreciated.
I was watching live data yesterday on my drive home and on my way in this morning a little bit more closely. As of now the Idle fuel trims have came back down to certainly acceptable levels. ST -1% to 2% and the long term give or take 4%. it seems that while accelerating the trims will both very quickly soar up high but if I’m going a constant speed and staying under an apparent magic number of 2,000RPM the trims level back off to what they were at idle. if I push it past 2,000RPM the trims climb quickly and anything over 2,500RPM maxes out the fuel trims.
Upstream is an A/F sensor, Not sure what it is “suppose” to read on a Subaru but it is averaging 3.6v-3.7v The downstream at Idle seems completely normal .1v to .8v fluctuating nicely unless much load is placed on the engine and it flat lines 0.000v with blips on 0.050-0.070 and back to 0.000
Have you checked your fuel.pressure and all while just in park.and aying with accelerator or while driving t as it happens would be something to check and what type of fuel injection does it have also?
hi guys, my first time on this forum, about me is that i m looking forward to start repairing cars after a long time (10 years), i dont hav really much experience but taking interset and learning everyday by all means.
if i make an input in this subaru case, it seems if external vacuum has been checked, then the internal vaccums leaks can be EGR, PCV or EVAp valve. pcv has been replaced and ithink evap line can be blocked somehow to check if eva valve is culprit.The last one will be EGR as it is little bigger job but always good and recommended to take it out and clean it. this egr valve deal with dirty exhaust gases so tends to get stuck open leading to lean condition.
pls correct me if am wrong.
thanks
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