Quote:
Originally Posted by porschefan76
Hello and thanks for joining in! I really appreciate the ideas. I've tried to use as few assumptions as possible while troubleshooting, so I like the application of Occam's Razor, but I'm not sure the data matches the assertion. I'll try to explain my approach below.
I have considered just changing the O2 sensors many times since this started as they're so cheap, but I resisted because according to Durametric, it all appeared to be working as intended (to me at least). The FORE cat O2 sensors were responding with a sine wave and the fuel trims seemed to be adapting by removing fuel at idle and adding it under load. I have never been able to get them to "peg rich" or "peg lean". Now, considering your comments, for the O2 sensors to be working properly, wouldn't it make sense for them NOT to be operating as a full range sine wave UNTIL the trims have adjusted? Do O2 sensors have a failure mode like this?
Shouldn't they be indicating either rich or lean through altered sine amplitude until after the adjustment? I have data that shows the O2 sensor output is essentially unchanged even as the RKAT value is changing. Some insight here would be invaluable. Perhaps it's because the amount of trim being added isn't that large (RKAT ~1.5-3.0 and FRA is ~1.25)? This is part of why I'm trying to find the short term fuel trim within Durametric, to compare with the O2 sensor output.
Looking back, I have specifications from Porsche I have cobbled together from this site and others and it looks like the O2 sensor range is 0.04mV less than or equal to "O2 Sensor Volts" less than or equal to 0.79 mV. I do have O2 output data with some values above 0.79mV, however in ScannerDanner's youtube videos, there are times he has said this doesn't matter much.
Can anyone confirm that 0.79mV is the proper hard limit for O2 output using Durametric Tool for a 986 01S?
Regarding the crankcase pressure, I've tested with a manometer and I am pulling -5.05 inches of water column, which is what it appears I should be getting. I honestly think the oil on the valve cover at the spark plug tube (this oil residue is new) is likely due to O-ring failure but, I'll put the manometer back on the oil-fill tube next time the weather cooperates.
I would be overjoyed to simply replace the AOS and the O2 sensors and be done, but I've done my best to avoid changing things that "appear" to be operating properly. If I can nail down an analysis that shows the O2 sensors are not performing correctly, I'll replace them.
Additional questions, what should the "Engine Load %" be at idle in Durametric? My data seems to indicate 19.00-20.25 at idle? Is this correct? If not, what does this point toward?
I'm open to any ideas on further troubleshooting! Also, I have no problem replacing the O2 sensors if the values above 0.79 mV indicate they're failing. Thank you all for your continued help!
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Sorry but I really can't comment on the specifics about the durametric readouts. My knowledge of afrs is limited to use of wide band o2 sensors and afr or lambda readouts, and narrow band sensors like ours can be very finicky. With that being said though my experience in working on cars has been two things 1 - it's really easy to overthink these types of problems 2 - you can spend forever looking up detailed specs, reference values, etc when that time may have been spent turning wrenches. I'm not knocking your approach at all, but rather criticizing all the time I have spent doing that exact thing when all I really needed to do was start physically working through things on the vehicle. The theory behind ICEs is really quite simple, and all things revolve around a few basic principles that will lead you to a diagnosis in nearly all circumstances. (I'm sure you've heard it before but don't lose the forest through the trees lol) I'm totally with you that the "eh let's replace this part and see what happens" approach is fool hearted at best but i trust the processes of reason and elimination more than anything when it comes to complex problem solving. Not to mention that Amazon's return policies are great, so try a new part and if it doesn't fix the problem clean it up and send it back and then let someone else buy it at a great discount lol.
Anyway, I'm happy to help if I can. Good luck and keep us posted!
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