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This afternoon I got involved on this vehicle because the guy on it is still learning and has replaced quite a few components.
The vehicle came in with a P0171 "lean on bank 1" and he found a big split on the intake hose. He taped it up for now since it's
a busy holiday season and we couldn't get another one yet and after more issues he replaced the MAF sensor and tried a new idle
control valve.
This is where I got involved and suggested we check fuel trims. This is something I'm learning to do more since joining this forum.
I found that at idle we had 20% LTFT and STFT was climbing to 25% - this after after taping up the split hose. We did a smoke test on the intake and found no leaks - slight smoking out the pivot point of the throttle body but the normal amount from my experience.
Then I got out my new vacuum gauge and got around 20 inches which went up to 25 when slightly above idle. Idle switching is working as well.
Next we checked o2 sensor voltage vs fuel trims. I found that the o2 sensor was close to 0 for a while then STFT slowly climbed over a few seconds until it got to
25% then suddenly the o2 sensor would jump up to 0.8v and soon switch back to 0 to repeat the process. When the engine is hot things get worse, just above idle the engine surges rapidly like clockwork in time with STFT switching along with the O2 sensor which is now switching about once per second, you see them both on the graph pulsing up and down exactly in time with engine revs going up and down.
If you suddenly release the throttle (even though it was barely off idle) there's a good chance it will stall.
With the o2 sensor disconnected it is slightly better but still surges.
at one stage I was a bit confused - the O2 sensor stuck on 0.8V while the STFT was at 25% and it just stayed there for a minute and the exhaust was pumping out puffs of black smoke - it knew it was running rich but kept the fuel trims up? A rev fixed that.
Then we did a few KOER tests, one of them suggested a pending fault for a misfire on cyl 1 and a little later for open circuit injector on cyl 1. That was only on KOER tests, never any other time.
Another KOER code that kept coming up was for low voltage at the MAF sensor - it stayed at 1.2v at idle and with a rev went to 4v.
We checked fuel pressure which stayed at 60 psi the whole time.
I did find a service bulletin for PCV valves for this engine - not sure if that could cause the surging though.
Getting involved in discussions because I have a lot to learn still.
vb4me wrote: Why did this not show up on the smoke test?
A smoke test applies pressure which pushed the split closed - it was sucked inwards before.
Someone has suggested to me that in future I should start with very low pressure smoke to prevent
that happening.
Getting involved in discussions because I have a lot to learn still.
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