P1126 and low rpm hesitation - all troubleshooting listed- Help greatly appreciated!
 

Hello all. I'm hoping to get some help solving some issues with my "new-to-me" 2001 Porsche Boxster S 6-spd manual. I purchased the car in December of 2019 with 52,500 miles on the original engine and it ran perfectly until early November 2020. The car now has 56,980 miles on it. The issues began with a momentary perceived lack of power while merging onto a major highway shifting into 3rd gear and a check engine light later that same day. I purchased the Durametric tool and read a P1126 code, no others. The car wasn't acting up significantly until I cleared the P1126 code. Once I cleared the code, the engine began to idle poorly while cold and would backfire into the intake manifold when pressing the gas pedal, especially a sharp rev.

For reference, when cold, the engine has a tendency to perform much like the engine in this video around the 8 minute and 55second to 9 minute mark: https://www.youtube.com/watch?v=hddx5Ux1v4Y

It has not stalled on me, even when backfiring into intake etc. Once warmed up, the engine still hesitates going back on the throttle following shifts, but idles well and runs smoothly above 3,000 rpms. Fuel economy is terrible, I'd estimate at 12-15 mpg. Previous to these issues, fuel economy was over 20 mpg.


I got to work:
1. Removed and cleaned the MAF sensor with CRC MAF sensor cleaner. Cleaned/dried thoroughly twice - NO CHANGE
2. Replaced the air filter and removed the connector to the MAF and drove the car - NO CHANGE
-assuming this means good MAF, also when warmed up MAF data from Durametric matches Spec (15-16 kg/h at idle) with MAF connector installed
3. Dug into intake manifold, removing the throttle body, plenum and resonance tube and cleaned thoroughly and reassembled - NO CHANGE
- very little to no oil in intake. AOS tubes in good shape. Oil fill tube outside coated in oil and dust but no visible cracks. Cleaned the tube for reinspection at a later date.
4. Smoked the intake using a smoke machine, finding no smoke emitting from the intake - NO CHANGE
-smoked long enough for smoke to stream from the oil fill port when I removed the cap
5. Ran a full bottle of Techron fuel system cleaner in a full tank of gas. - NO CHANGE
6. Removed fuel filter and tested the fuel pump flow rate using the steps in the Bentley manual. Pump flowed 1.25 L in 30 seconds (exceeding spec 850mL in 30 sec) - NO CHANGE
7. Replaced what looked like the original fuel filter and tested the fuel pressure at the fuel rail. 3.8 bar with engine off and 3.3 bar with the engine at idle, meeting specifications in the Bentley manual - NO CHANGE
8. Tested vacuum at the oil filler with a manometer. With engine fully heat soaked, read between 4.95 and 5.05 inches of water column, meeting specifications I've found online. - NO CHANGE
9. I've purchased new fuel injectors and fuel pressure regulator and will replace the original fuel injectors (along with pressure regulator while the fuel rail is out) when the weather improves so I do not crack the plastic window (I do all work in unconditioned garage or outside).

The car leaks no fluids. I replaced the water pump, thermostat and coolant in May 2020. Spark plugs were replaced in June 2020, coils in excellent shape, not replaced. Spark plug electrodes were worn, but the plugs were not fouled. I changed the oil & filter at the 6 month mark with 2,900 miles on the oil.

Only knowns worth mentioning:
1. Original clutch, original IMS (at least no records indicating otherwise). Planning clutch/IMS when the weather breaks.
2. Camshaft deviation on bank 1 is -8.2 degrees (out of spec: +/-6deg) Still doing research but considering an engine out when I do the clutch to replace cam wear pads as well as chain tensioner. Bank 2 in spec at -4deg. Dropped oil pan when I bought the car, a few specks (maybe 15, size of ball point) of dark brown plastic in there. Have monitored since and no additional plastic in the oil or filter. Have 6 oil changes (back to 43,000 mi) worth of UOA's and all are good; 2 from me and 4 from P.O. (yes, I know this doesn't mean anything other than "so far, lucky")

I have driven the car 250 miles total throughout all of the steps listed above. I have captured data from durametric while driving on 3 separate occassions. I captured RPM, Banks 1&2 FRA & RKAT, banks 1&2 pre-cat O2 sensor & post-cat O2 sensor voltage, MAF hot film and voltage and intake air temperature if anyone is willing to dig into it. The only data I'd call "suspect" that I captured would be the post-cat O2 sensors, which appear to change while driving (voltage moves up and down) but they remain steady at ~0.74 mV on both banks at idle. The RKAT values shift from 0 to -2.4 on both banks and FRA shifts from 0 to 1.3 on both banks throughout the data acquisition period (I reset the ECU to clear the values and watch them change as I drove the car over time).

I've also actuated both bank Variocam at idle using the Durametric and I can verify that they are both functioning properly, causing the sound/feel of engine to change noticeably when activated.

I'm hoping for some experiences as I know this code and these symptoms are not rare. I've read every forum post I could find and I've tried to follow the troubleshooting steps in those posts, but I'm not getting any success. I've attempted to be succint and demonstrate my version of a methodical approach to troubleshooting the issues. I'm willing to try additional troubleshooting steps and procedures and answer questions as time permits. Thank you for your time!

Best Regards,

Rich

P.S. - should I post to other forums as well and if so, which?

Do you still get the P1126 code?
Is it the only code you get?
Any pending codes?

I'd start pulling the fuel injectors, looking at the tips for carbon fouling.

RKAT is the adaptation value near idle.
FRA is the adaptation value under load and further divided into FRAU (lower load range ) and FRAO (higher load range) ranges (perhaps the durametric doesn't display these divisions).

The RKAT values near idle are used to change the length of the injector pulse to account for deviations from ideality (ie intake leaks) to maintain the proper O2 sensor reading. The RKAT value is an additive factor and can deviate by +/- 4.5%. The FRA value is a multiplicative factor and can deviate by 1.32 to 0.70. The positive values or values greater than 1 increase the injector pulse length to account for a lean mixture, and negative values and values less than 1 are to compensate for a rich mixture.

First, thank you both for responding so soon.

P1126 is the only code I get legitimately. When I ran with MAF disconnected I got some codes for the MAF, but not since reconnecting. Also have not gotten P1126 back since first time. No additional pending codes.

Great, as soon as it gets warm enough to mess with the plastic window, I'll pull the fuel rail and look at the injectors as I change them.

I guess Durametric tool does not divide further because I do not see FRAU or FRA0.

RKAT values of -2.4 indicates rich at idle and FRA 1.3 (positive) is lean above idle then correct? I was considering smoking the intake again but if it's over-rich at idle, likely unwarranted?

Anything else I should be checking? Thank you for your time!!

You may be seeing a lean situation because the one or more injectors are carboned up and not delivering a full pulse fuel volume.

OK, this is kind of where I was going when I ordered the replacement fuel injectors, so hopefully, I get some progress there.

One more question, the -8.2 bank 1 camshaft deviation alone should not be enough to cause these hesitation issues etc, should they?

Thank you again.

Following your issue with interest.
Please post results once you have changed out the injectors.

Will do. Thank you for your interest and help!

It looks like I might be able to get the top in to service mode this weekend, so hoping to get to the fuel injectors.

Likewise.

My codes are clear after changing out all 4 O2 sensors, but still get lingering short periods of bogging, or lack of power. Have never stalled.

I had a 2001 986 as well with the same issue and ran thru all those fixes as well. Have you REPLACED the MAF?? Just an idea.

Here is the 986 DIY playlist of videos I did on my car's issues.

https://www.youtube.com/playlist?list=PLbBMHPz04qDW2lbqUZ4p2yWK9joftSOEO

Brian :)
HTTP://986Brotherhood.com

Wow, this community is awesome. Thank you all for continuing to follow along and helping. I've currently got my heater running in my garage trying to break it into the 50's so I can get some work done today.

I've got my Durametric data and it appears that my pre-cat O2 sensors are working as intended. I'm fairly certain my post-cat are working properly as well, as they maintain a steady mV reading at idle, but they do change as the revs change. So, I haven't considered changing those yet, but might be something I'll do if it's recommended. Again, I've got my data and plots if anyone wants to dig in, but this is not my profession, so I only know what I've read about this data/plots.

I actually make reference to your video in my OP. They were very helpful and helped clarify things when I checked for fuel pump volume and fuel regulator pressure checks, so thank you! I was really hoping my problem was fuel pressure as it has a tendency to backfire into the intake and lope similar to your car in the video when it's cold, but not when warmed up.

I'm really hoping replacing the fuel injectors gives some results, because after that, I'm not even sure which animal to chase next. As I mentioned above, my bank 1 camshaft deviation is out of spec, but not enough to throw a code, so I am not sure if that is contributing to the issue or not.

Hello all, just an update. I was able to get the temp up in the garage and got to work. The P1126 CEL that started all of this was for bank 2, so I started there. It took a little longer than I anticipated, so I only got bank 2 fuel injectors replaced. I'll do bank 1 when I get some warm weather again.

Unfortunately, there was no real change to the idle/throttle condition. Upon first start the engine still responds very poorly to throttle input. Backing down the driveway, response improves slightly, but not much. I left the engine top cover off for the first 5 minute drive so I could monitor for leaking fuel at stop signs. With that cover off, I can clearly hear swooshing noises when I crack the throttle, especially on blips. At one point, when I was first pulling away from the driveway, I could even hear a whistling noise, so I'm convinced this must be a vacuum leak. Another run at the intake smoker when the weather gets warmer.

Anyway, in frustration, I took a quick (and annoyingly shaky) video with my phone to listen to in an attempt to locate the noise. It appears to me to be coming from the vicinity of the throttle body. I've decided to upload the video and post a link in this thread in case anyone wanted to take a listen and see if it sparks any thoughts on further troubleshooting.

https://vimeo.com/501941938 (truly sorry for how bad this video is. I might make a more patient attempt soon)

I think I may get a unidirectional microphone I can move around the engine and listen while a buddy hits the throttle as well, to see if i can really narrow it down. I have avoided using the "spray carb cleaner" step the whole time, but I might do that tomorrow in the area where the infamous J-tube connects to the plenum.

So, I guess right now, my question to you folks is, "Do you think the sounds in the video I linked indicate a vacuum leak?" Please feel free to let me know what it could be if it does not sound like a vacuum leak as well. As usual, thank you for your time!

you have a interesting situation there.
Backfiring into the intake would indicate a vacuum leak
The sound in your video sounds somewhat like a vacuum leak.
But on the other hand your low RPM fuel trims (RKAT) are negative values indicating a rich condition at idle. Vacuum leaks cause lean conditions at idle. Your mid to upper range fuel trims look to be positive values which you would expect under load at mid to upper RPM range. Adding fuel under increased engine load.
Porsche and or Durametric expresses fuel trims in a manner that I am not very familiar with so I could be off on what I think I see.

What are your pre cat o2 sensors doing at idle and again at say 3000 RPM???
If fuel trims are going negative at low RPM I would expect the O2 sensors to be showing a rich condition. Voltage above .500 mil volts then dropping as RPM increases and fuel trims go positive.
The sound in your video also (to me) sounds a little like a possible exhaust restriction.
Any chance the Cats are plugging up??

Don't know if I have helped or added confusion:eek:
But those are my thoughts

Hi again! You're absolutely helping and I appreciate it. OK, re: the exhaust, I have not done any troubleshooting there. What's the best way to know if my cats are plugged? I will do some searching and see if I can find some posts. Would the engine operate smoothly (more smoothly, still down on power) at higher RPM and experience the bulk of the issues at idle if the cats were plugged? Would I get a CEL if the cats were plugged? I'm interested in performing any suggested troubleshooting.

Regarding the RKAT and FRA data, your thoughts echo my own, which is why I was hoping I had a non-functioning fuel injector(s) (open at idle more than it should be going rich, but not delivering enough fuel at WOT resulting in lean at higher RPMS). I have some data plotted, I'm not sure how to get the paste in from excel, so I'll try posting some image captures of the data.

https://imgur.com/caHk1v1.jpg
https://i.imgur.com/Udv3RuJ.jpg
https://i.imgur.com/ZpJ1QGS.jpg

If anyone would prefer, I can take a shorter time snaps, to open up the plot a little more if the data isn't clear enough. Unfortunately, I don't think I have/plotted MAF voltage, but iirc, it was within Porsche specifications, thus I haven't replaced the MAF.

Thanks again for all of your time!

Looking at the post Cat O2 signal I would say your cats are not working.
Post Cat signal is following RPM and Pre Cat signal very closely. Not as it should be.
Post Cat signal will have some rises and falls with RPM and engine load but should be biased towards a flatish signal voltage in the .650-.750 mil volt range.

There are some good youtube videos on testing for exhaust restrictions.
Also if you look up ScannerDanner on youtube he has some very good videos on reading fuel trims and O2 signals to diagnose performance problems.
He is a professional and very good at what he does.
You can view his videos and have a visual of what your Post Cat O2 signal should look like (flatish) under different running conditions.
Perhaps some of his videos will give you some insight on your issues.

OK, I'm going to follow this and see where it leads. I've watched Schrodingers Box on youtube and he's where I got my primer on fuel trims, but ScannerDanner seems great as well. In fact, I'm watching this video now:
https://www.youtube.com/watch?v=9TlygJMxTps
I may go purchase a back pressure gauge and check each of the cats. The only hesitation I have with this right now, is that in ScannerDanner's video, he said that because the pre-cat O2 sensor indicates rich at wide-open throttle, he'll focus on the exhaust and assume it's not a fuel issue. It does not appear that I am running rich (likely lean) above idle. I also do not have a situation where the car will not exceed a certain speed. It still "almost" drives like it did before above 3000 RPM. Additionally, my water temperature gauge has never indicated that the engine was running hot.
I may start by checking the temperature of each cat at the inlets and outlets and ensure the outlet temperatures are higher than the inlet temperatures, indicating the cats are heating the gases. I will also try to capture a stream of good Durametric data from all 4 O2 sensors while maintaining 2000-2500 RPM for a minute or two. I will post results once I get a chance to run these tests, hopefully this afternoon. Thanks!

OK, quick follow-up. I tested the temperatures of the "pre-cat" (cat on the header) and the temperatures were higher at the outlet end of the cats than at the inlet side, which is promising. I collected Durametric data for the O2 sensors while trying to hold the rpms at ~2000 RPMs for 2 minutes, followed by ~2500 RPM for 1 minute. The data is here:

https://imgur.com/FJZ4xl9.jpg
https://imgur.com/E1V82eR.jpg
https://imgur.com/t7FKVaE.jpg

The post catalytic converter O2 sensors appear to be responding properly, only showing big movements on throttle changes (to me at least. Please tell me if I am incorrect).
I went ahead and acquired a back pressure test gauge and O2 sensor socket and will attempt to check back pressure as soon as I am able. The weather is not going to cooperate this upcoming week.

As usual, thank you all for your time!

Following with interest.

Post cat sensor response may be ok. Not really sure.
Very very difficult to diagnose problems over the internet.
Another issue in diagnosing is that the Durametric expresses data over units of time (bottom axis on the graphs) as compared to frames when you watch something like ScannerDanner's video's. Makes comparing data a little more difficult.

You may want to look at ScannerDanners vids on Catalytic converter efficiency or his vids related to the P0420 or P0430 codes. In most of his vids there are examples of bad and good wave forms on the graphs. May give you better insight then I am giving you:D
I know you don't have the P0420 or P0430 code but your post Cat Sensor signals still seem a little suspect.
Hope I am not leading you down a wrong path.

Thanks! Weather just got bad for about the next week, so updates may be slow.

I definitely agree that the fidelity of the data from the durametric is troubling at times. The fact that the length of the time steps are inconsistent really gets to me. I will take in some more of ScannerDanner's videos and see if causes any ah-hah! moments. As soon as I can get those O2 sensors off and check the back pressure, that'll be a big data point on whether I need to focus on the exhaust to solve this issue or not.

Thanks again for following and helping!

I encountered the same issues (and same P1126 code IIRC) with my 2.5L this past summer and tried many of the same steps you tried like cleaning, disconnecting the MAF, checking for vacuum leaks, O2 etc.

I know you said you checked the intake already, but its worth checking again between the airbox and the screen just downstream of the MAF (assuming the S's intake also has a screen).

FWIW, the culprit on my car turned out to be a clear piece of plastic wrapper caught inside the intake on the screen inside the intake tube just downstream of the MAF. I'd checked the intake previously but I didn't find it at first since the plastic was clear and not very large (maybe 1" -1.5" square) and it might've been clung to the side of the intake.

Hi! thanks for the suggestion, I will definitely look into that. If I'm being perfectly honest, other than checking that tube for smoke during my smoke test, I didn't investigate the intake tube very closely. As soon as the temps get back above 30 (ugg!), I will take a look and report back. As usual, thanks all for your time!

Hello friends. Sorry for the delay in updates, the weather has not been cooperating.
Yesterday was the first break in temperature so I scoped the intake tube as suggested and there were no obstructions. I moved on to replacing the fuel injectors on Bank 1 (immensely easier than on Bank 2). I actually noticed some positive change in the cold idle, throttle response and general feel of the motor overall. The engine felt noticeably smoother on the test drive and performed much like I remember it performing before this all began. In addition, fuel economy seemed to improve, but it was based on visual gauge estimation, so not data.
This is not the end of the road though. The car stored a P1126 during the test drive and there is still a momentary "swoosh" when sharply pressing the throttle.
It looks like the weather will be improving again next week sometime, so I'll check the cats by removing the fore O2 sensor and checking back pressure on each side. I'll also try smoking the intake again. I also noticed that cylinder 1 appears to have begun leaking oil at the spark plug tube, so I'll be replacing all 6 of those as well (they're on their way).
I do have a question though regarding P1126. Can anyone give me the correct verbiage for P1126 on DME 7.2? I realized my Durametric is reporting it as P1126 - Porsche fault code 356 - Multiplic. mixture adapt. lower load range B.1: and the Bentley manual reports it as P1126 Porsche DTC 35 - Oxygen sensing area 1 cylinders 4-6 - Short to B+/above upper limit/rich mixture threshold. Is P1126 a Bank 1 or Bank 2 code on 7.2? Any help there is appreciated!
I'm also planning to do a "hard reset" and capture some fresh data. Can anyone with a Durametric and DME 7.2 tell me what the short term fuel trim entry is? I was under the impression it would be "oxygen sensing Lamba" or "fuel trim mean value" but I do not see either in the list of Actual Values.
As usual, thank you for your time and help!

Hey fan, late to the party but I have a couple of thoughts...

Intake backfire is a lean condition (so long as timing is not completely wrong, which would be impressive), and if your o2 sensors are reading rich at that time if be would be very suspicious. A new set is not expensive, it may be worth a try.

Are you still pulling vacuum at your oil fill tube? May be worth double checking - i have read (not personally experienced though) that if you lose vacuum to aos then your crankcase pressure will build up and the you will notice this when the plug tubes start to leak oil.

Occam's razor - fouled o2 sensors reading too rich, engine pulls fuel in response, lean condition causes intake backfire (at idle only as the system will run richer under load), fries AOS tube, created vacuum leak, lean condition is now worsened and plug tubes are leaking oil. New injectors may have helped band aid the problem but I don't think they were the chicken or the egg.

Anyway, just a thought.

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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!

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!

Sent from my POCOPHONE F1 using Tapatalk

Hey, thanks for the quick response. I've got to admit, I am beginning to be tempted toward just replacing a few things (especially the low-dollar stuff) and see what happens.

I think if I can't get specifics on where the O2 output signals should be or what the STFT PID is in Durametric, this limits my ability to continue troubleshooting with any reliable effectiveness. But I cannot find any confirmation that maintaining a full-sweep sine wave of 0.04mV to 0.85 mV is even a failure mode for narrow-band O2 sensors, meaning logically, they're working and it's something else. That said, after I test the cats with a back-pressure gauge, replace the spark plug tubes, test crankcase vacuum with my manometer again and smoke the intake once more, my next step may be replacing the O2 sensors. Fortunately, I enjoy working on the car and learning more about it, so I'm just going to keep at it.

Thanks for the time and the help!

From what I see in your O2 signal sine waves that you have posted in this thread in post 13 your O2 sensors are fine they show a typical sine wave.
The issue I see is your post Cat O2 signals are showing that your Cats are not working properly. So the Catalytic converter are suspect the sensors are fine.

Sorry I just went through the thread again and see in post 17 that you ran the O2 sensor data again at a more steady rpm.
But to me your bank 2 post O2 cat sensor still shows that your cat on bank 2 is suspect. maybe not failed but boarderline.

Hey blue do you think a failing cat would cause his problems though? I could see that if a cat were clogged and not flowing well that would cause loss of power because of choking down flow. Would out cars attempt to lean out the mixture in order to reduce emissions if it senses a bad cat? I'm not asking to disagree, it's purely from ignorance I've not ever dealt with a bad cat before and I'm trying to piece together how that would play into what he's dealing with.

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Hello and thanks for the follow-ups. Yes, I intend to back pressure test for failing cats when the weather cooperates, probably early this upcoming week. As far as I can tell however, the post-cat O2 sensor does not play with the ECU, so I don't think that could be causing the P1126, but maybe if the cat is failing, that could cause it?

I'll add results as soon as I perform the test. Thanks for the continued interest and inputs!

Agree your P1126 is another issue.
Perhaps some form of vacuum leak.
Or MAF sensor but there are ways to test it.

Yes, I agree. As you pointed out though, the downstream O2 sensors do look like something is up, so I won't ignore them.

The MAF appears to be operating properly, 15 kg/hr at idle and the Voltages looked about right last time I pulled data. I pulled some data on my test drive after changing the fuel injectors but I was in a rush and I'll need to pull more. Will pull MAF, O2, Fuel Trim and Engine Load data next test drive after I test cats, smoke the intake and replace the spark plug tubes.

Thanks again!

A test I do is compare MAF signal to Throttle position sensor signal.
There is a direct correlation between the two.
I hook up my Durametric and put the MAF signal and the Throttle position sensor signal on the same Graph. Then I take the car for a good long drive.
I set the laptop on the passenger seat so I can watch the two signals.

What you should see is the two signals paralleling each other. The TPS signal is slightly smoother then the MAF but by very little. That just the difference between air movement generating one signal and mechanical movement generating the other signal.
So you should see Both signals following your foot so to speak. If your very smooth on the throttle both signals should increase with the same smoothness. If you floor it both signals should react the same way. If your smooth on the throttle or holding a steady RPM both signals should follow each other. If you see something erratic in the MAF signal when your throttling smooth or holding a steady RPM then there is an issue with the MAF.

I do this with my car over a 52 mile loop. Gives me every driving condition one would ever encounter. City stop and go, to country flat out, hills, curves the works.
Actually a fun test to do.

This sounds great. I'll include throttle position sensor output in my data pull the next time I am performing a test drive.

So, I've been doing further reading on the pre-cat O2 sensor because now I'm stuck on the fact that the output of those sensors does not appear to change while the fuel trims are being modified (ie. in Post #14, the Bank 1 and 2 pre-cat (FORE) sensors display almost the same sine wave while the RKAT is at 0 as it does when RKAT moves to -0.25 to -0.75 on all the way to -2.5). If the ECU is adjusting the fuel trims negative as a result of O2 sensor feedback loop reporting rich (my understanding of the function), shouldn't the O2 sensor display a sine wave that looks like it's seeing rich? I'm considering inducing a LARGE vacuum leak at idle while pulling data and see if the O2 sensors respond to this by indicating lean, at least for a couple of seconds. ScannerDanners videos show lots of response from the O2 sensors while he is changing various inputs (pressing the gas, inducing vacuum leaks, plugging vacuum leaks, etc) and my sensors don't seem to display any of that. Is this specific to the operation of these sensors? Maybe they're just bad and 200 bucks will fix these issues? I really need to see STFT to better understand this I think.

Again, any input is greatly appreciated. Thanks!

Hi all. Just a brief update, following the advice of ike84, I checked Amazon for the Bosch oxygen sensors. I'm not sure why, but I haven't purchased parts for this car from Amazon before. Anyyyyyyway, the sensors have full refundability and were at a lower price point.

Plan now will be to swap in new O2 sensors when I pull them to back-pressure test the cats. I will perform an overnight "hard-reset" (poor-mans handover) of the ECM the night before and, provided cats pass the back-pressure test, go for a test drive and collect a good deal of clean data with (hopefully) known-good cats and new upstream O2 sensors. I'll report back following these efforts.

As usual, thanks all!

Happy hunting! Keep us posted

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1. I do not see a failing Cat causing his problems.
2.Our cars do not attempt to lean out the mixture in order to reduce emissions if they sense a bad Cat. Post Cat sensors on cars of that era do one thing = monitor Cat health via reading oxygen levels.
The only thing a narrow band O2 sensor of that era can do is sense oxygen and only in a very narrow band.
3. The reason I pointed what I see as possible failing or bad Cats is that he was talking about replacing his 02 sensors. I was pointing out that based on what I see in the O2 sensor Sine Wave, that the Sensors are fine. But the post Cat signal is suggesting a failing Cat.. So no need to replace the O2 sensors.

Ummm I think that's it :D Hope I answered your questions.
And there is nothing wrong with disagreeing how else could one learn he was wrong;)

So I need to go and watch scanner danners videos about cats because my knowledge of them is still very much comic book version. When they fail what is the main symptom? Do they choke down the exhaust and kill power through reduction of flow? Or do they just stop cleaning up the exhaust and result in no other difference? I remember newarts video of how he toasted his cats when he blew his engine but that's the only other time I've ever heard of them going bad.

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Yes, ScannerDanner and also Schrodingers Box on youtube have great videos on fuel trims, O2 sensors, failing cats etc. ScannerDanner is a professional and Schrodingers Box is a DIY guy, so the videos are different, but both focus on the mathematics and science of engine controls.

From what I've learned watching their videos it appears that your former statement is what occurs. The failed cats typically impede the flow and result in very poor engine response and a lot of hot start issues. That said, I see exactly what blue62 was referring to with respect to my downstream O2 sensors. With the car at a steady rpm, a properly functioning cat should result in a downstream O2 sensor with a very flat output. My downstream O2 sensors do not look like they are doing that. Hence, a back-pressure test, to see if the cats are clogged or failing ... or at least that's my understanding from watching ScannerDanner and asking questions of my mechanic buddy.

Cats fail in a number of ways.
1. Physical damage such as hitting speed bumps. Can lead to a rupture,hole, leak in the case.
2. "Plugging up" usually caused from things like too rich of mixture over time. rings not seating causing oil blow by, leaking head gasket. Antifreeze gets into the exhaust.
3."Burning out" caused by to lean of mixture, excessive idle time, things that create to much heat.
A burned up cat has no back pressure issues or the like, it acts just like a good cat except it doesn't do it's thing.
Those are the things I am aware of.

They are designed to last the life time of the car. But they function in a very narrow range. So fuel air ratio needs to be very close to 14.7 to 1. I think somewhere around one half of one percent + or - of 14.7 to 1. Outside that range for extended periods then they burn up or plug up.

So something to try and keep in mind when dealing with OBDII and the P-Codes.
Its not about engine performance or power or gas mileage. The primary function of the OBDII system including the sensors is Catalytic Converter Performance and longjevity. Everything else is secondary.