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Thread: Bad O2 Sensor?

  1. #1
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    Bad O2 Sensor?

    Hi all, so good news! First fire today went very well. Started right up and ran great (maybe). So, after I shut it down I was looking at the logs and my long term fuel trims were maxed on bank 2. This seemed to indicate that I was running lean on that bank and the fuel was being added? Anyway, I pulled the plugs and they were black. Bank 1 plugs looked good. I could tell it was running rich because I almost asphyxiated myself. LOL. Anyway, I am thinking that maybe the O2 sensor is not reading right. It's maxed out at times (>500?). I don't know how to attach my log but it seems to be out of sight to me. It ran though.....I'm just looking for some ideas to look at. I have another sensor and was thinking about swapping it out just to see change if any. Where can I find out how to post my log? Sorry, big noob here. Oh, maybe this will work.
    Thanks, Keith
    Start #2 5-20-20.hpl

  2. #2
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    If you think it is the O2 sensor bad, swap 02 sensors. That way you have 2 known results and if they flip flop then you have your answer.
    It can be many reasons 1 bank is rich or lean and this test verify if its the sensors. OR Looking at the log the fact that you are running rich and the o2 sensor mV are oscillating your o2 are good. When you increased the throttle if it were only an intake leak on Bank 2 causing the need for extra fuel the STFT would be fairly normal because it would have found the new norm and set the new baseline in LTFT high STFT steady. Not your case. Both the STFT and LTFT are adding fuel because its "lean" AND only on B2 yet plugs are fouling because rich. Look for an exhaust leak before the O2 sensor. When you increased the throttle it corrected both STFT and LTFT but only a little because more exhaust pressure was preventing as much infiltration of outside air. Try raising rpm again, increase to >2000 and hold watch trims.
    If it was bad fuel pressure both banks affected and increasing rpm would make it worse. Bad MAF again both banks would show it. There may still be an intake leak on B2 but it is not the only issue and like I said it would have set a new normal in LTFT and STFT would be closer to 0.
    Last edited by Hondaeater; 2 Weeks Ago at 01:08 AM.

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    Thanks for the input on this! It does seem like affecting one bank and not another eliminates a lot of things. I did note the bank 2 injectors had a pulse width about twice the bank 1 injectors. Is this controlled by the computer by bank? Am I right that the engine is in closed loop during warm up so I never went to MAF? Also, how do you clean the spark plugs that I sooted up. I will change out the o2 to see if it makes a difference. Additionally, I have a Elgin 1218 cam and the headers are open right now. The o2 sensors are about 4 to 5" inside the collector. Any other ideas are always welcome! Thanks, Keith

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    Quote Originally Posted by marko1957 View Post
    Thanks for the input on this! It does seem like affecting one bank and not another eliminates a lot of things. I did note the bank 2 injectors had a pulse width about twice the bank 1 injectors. Is this controlled by the computer by bank? Am I right that the engine is in closed loop during warm up so I never went to MAF? Also, how do you clean the spark plugs that I sooted up. I will change out the o2 to see if it makes a difference. Additionally, I have a Elgin 1218 cam and the headers are open right now. The o2 sensors are about 4 to 5" inside the collector. Any other ideas are always welcome! Thanks, Keith
    Yes you can see the firing order in the tune for each bank. Engine>Fuel>General>Injector Control>Bank select but do not change that. Yes you will show a higher PW on bank2 because it IS adding the fuel, but the sensor is still reporting lean but open headers, you cannot use the data. Did raising rpm and hold change the trims?
    List the mods done and your base and current tune if you would. Add the tunes the same way you did the Scanner log.
    You went CL about 1:11 seconds in Scan. The LTFT are static at 25%, reset them in the Special Functions in Scanner after you reach operating temp. and definitely after adding length to the exhaust.
    Open headers will definitely give false readings. You need at least 2' after merge collector to have accurate data. When you add the exhaust make sure you weld a bung in for WideBand O2 just plug it until you get one.
    Add the MAF Channel in Frequency and Cylinder airmass. Add delivered engine torque, and AFR.

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    Hondaeater, you are the man. I will do as you suggest. I'm getting ready for a start and will report my findings at higher RPM. I'll list mods and tunes at that time. Thanks for the help! Keith

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    Here's the latest

    Ok, I have a 5.3 out of a 2005 Tahoe with a 4L60E. I installed an Elgin camshaft (sloppy stage 2) and springs. I removed the truck manifold to fit under the stock hood. I installed a LS1 manifold and injectors (1999/2000). I have a 2600 stall coverter and 373 rear. I'm running long tube headers but need the pipes. I copied the injector data from a 2000 corvette. I will attach runs #3 and #4 along with my original file and the latest with the injector data changed. Hopefully this will help as I think I've fouled a plug or two on bank 2.
    Start #3 5-21-20.hplStart #4 5-21-20.hpl2005 Chevelle PCM Original 5-3-20.hpt2005 Chevelle PCM Copied LS1 Injector data Short Pulse Limit 5-17-20.hpt

  7. #7
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    If there is no exhaust past the headers you can't trust anything the o2 sensors say.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

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    Yes, I'm going to add some pipe to the headers asap. Hopefully, it will settle things down a bit. I'm happy it runs but I don't want to hurt it. I almost know enough to do that for sure. Thanks for the input, all is welcome. You guys rock!

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    Hi all, I was reading on here and came across another thread where it was recommended to remove 5-10% from my VE table under 2000 RPM's since I'm running a bit larger injectors. Not withstanding the exhaust changes I'm making for the o2's (ordered parts tonight), does this advice make sense to you all? Just doing research and was curious..... Thanks, Keith

  10. #10
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    1. get a wideband

    2. set the computer into OPEN LOOP (disable O2 feedback)

    3. Log the wideband data to a high resolution table using scanner

    4. Tune the VE map / Maf to match desired a/f targets

    5. Re-enable closed loop and verify there is a tight wander

    'desired a/f targets' generally based on Engine Pressure

    0-40KPA traditionally cruise region tune to 15.2:1 if leaving open loop, otherwise target 14.8 or 14.9:1
    40-50KPA should approach 14.7 from 14.8
    50-75KPA is transitional, value should start around 14.6:1 and slope down to 13.5~ by 70KPA
    75-85KPA is nearing WOT, value should move from 13.3's into 12.8's or even 12.5's for higher compression engines
    85-100KPA is WOT for naturally aspirated engines, most respond well between 12.5 to 12.0 a/f ratio

    HPtuners uses something called Power Enrichment to add the extra fuel past a certain point. Advanced tuning topics would having you enrich the VE map directly for the transitions to avoid PE at pressure BELOW(less than) say, 80KPA
    However many people choose to let PE do the 'work' from 50KPA+
    Its up to you how to tune the engine but personally I NEVER used closed loop because I prefer 15.2 to 15.8:1 air fuel ratios (fuel savings, perhaps 2 or 3% but meh) in cruise regions.

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    Do you have the VIN from donor Tahoe? If it was flex fuel it could actually have had better flowing injectors than the 2000 model you got from Camaro/ Vette. A 2000 5.7L Camaro is 26.4lb/hr, 2003 Vette I had 29.1 lb/hr injectors stock and the 06 suburban flex fuel is 35.4lb/hr
    Did you use the fuel rail from Tahoe? It would have had a vacuum regulator on the rail to manifold. A Vette uses a filter regulated dead head rail.

  12. #12
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    Hi, so I do have the VIN from the tahoe. It was not a flex fuel. I used the Corvette filter regulator and aftermarket rails with a front cross over hose. I still have the original manifold and rails. I used the DBW throttle body from the Tahoe instead of the Cable throttle body that came with the intake and injectors. It's interesting that at initial startup it seems to run fine but after a few minutes it changes. i'm pretty new to this program so I'm flooded with information and it's hard to determine a direction. I did try to go closed loop but I failed to delete LTFT history so they still seemed to kick in. Still went rich. I found that my idle table was allowing the engine to idle at 675 at one point so that also didn't help. In looking at other posts ect. I also think I didn't adjust the secondary VE table when I adjusted my primary. i know I'm a mess. I was trying to go Open Loop to see if it would make a difference by taking the o2 sensors out of the equation but by not deleting LTFT history I think it didn't help. I was following the sticky here as best i could but still learning.

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    Your Idle> base setpoint table, if you think it needs to be 900rpm at normal operating range, would stand to reason that at lower temperature it would need even more. You should make adjustment to entire table from stock adding about 200 rpm for continuity.

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    Hondaeater yes I changed my idle request to 800 across the board just to see if it would settle down a bit. It didn't change things regarding the richness though. I tried again today with those parameters and have attached the log for review. I did note that my MAF calibration table says that with 3,177 Hz it would expect approximately 75 g/s. My log shows 9.6 g/s (SAE) with a corresponding 3,177 Hz. Does that make sense or am I missing something?2005 Chevelle PCM Copied LS1 Increased idle to 800 entire table 5-23-20+.hptstart #7 still rich 5-23-20.hpl

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    Have you added the exhaust yet? Making Base setpoint 800rpm across all temps like that is not recommended but I'm sure you were just testing the result. You will need a bit higher when cold and the idle comes down as ECT rises. Add 200 to the Original table would keep it proportional to ECT.
    Please explain what you mean about the Freq and expecting 75 g/s? Your Airflow vs Freq table in g/s units shows to be 8.95 @ 3125Hz - 9.9 @3250Hz ?

  16. #16
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    Hello, I've ordered a AEM wideband, ordered the piping and I re-checked all the o2 wiring from the ecm and fuse box just to make sure it wasn't something I did. The whole question about the calibration of the MAF was me going down a rabbit hole. I haven't seen enough yet to know what is normal and within range or way outside the box. I'm sure as I look stuff up and see other peoples logs I'll start getting an idea of what's average/expected based on the build. Yes I just wanted to see if the higher RPM would tame the o2's. I was looking at the MAF calibration in my tune. I didn't change it from the stock tune but as I'm researching the log I'm trying to find when the engine changes. I can hear it happen. I think it might be when it goes into closed loop? I'm just fishing but won't do anything further until I get the exhaust and wide band as suggested. I'll have to wire the wide band into the EGR for it to work I believe. Thanks for the help, Keith

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    Quote Originally Posted by marko1957 View Post
    Hello, I've ordered a AEM wideband, ordered the piping and I re-checked all the o2 wiring from the ecm and fuse box just to make sure it wasn't something I did. The whole question about the calibration of the MAF was me going down a rabbit hole.
    I haven't seen enough yet to know what is normal and within range or way outside the box. I'm sure as I look stuff up and see other peoples logs I'll start getting an idea of what's average/expected based on the build. Yes I just wanted to see if the higher RPM would tame the o2's. I was looking at the MAF calibration in my tune. I didn't change it from the stock tune but as I'm researching the log I'm trying to find when the engine changes. I can hear it happen. I think it might be when it goes into closed loop? I'm just fishing but won't do anything further until I get the exhaust and wide band as suggested. I'll have to wire the wide band into the EGR for it to work I believe. Thanks for the help, Keith
    Do you know how to use the Histogram in the Scanner graphs? There are no short cuts. Looking at someone else's MAF calibration is not going to help you tune YOUR motor. Using the histogram will reveal where your MAF is out of calibration and give you the precise data points to fix it. Until you get the exhaust sorted out you cannot use a WB or a NB for tuning. This may help explain the LTFT and STFT data and what to do with it.
    https://www.youtube.com/watch?v=Rhg5NSh8Dq8

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    Hi all, so I finally got my additional pipes installed and as you said it helped a lot. Although it's running rich still at least the PCM is recognizing it and it's on both banks. Pretty happy with everything as now I can start tuning it. You were right on with the needed extension from the o2 sensors. Anyway, I did see where a suggestion was made to copy a VE and MAF data from a LS1 so I tried it but it actually was quite a bit worse to me so I went back to previous tune for now. I'll attach the latest scan for any input on direction that you recommend. I still am waiting for the rest of my exhaust so I can install the wideband. Thanks for the help! I almost have some idea of what's going on (I hope). Thanks again, Keith

    Start #11 better with pipes 5-30-20.hpl

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    If it's still a little rich like that right now, take the MAF and VE table and minus 5% from both tables. Save it and flash it, that should start to bring the fuel trims down. Do it slowly as to not over shoot and make it too lean when you start driving it.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

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    5FDP, that's what I was looking for, direction. I truly appreciate the time you take to answer our questions. Makes this journey much more bearable for us until we can get our bearings. I'll keep at it and let everyone know what I discover. Hopefully it will help others too. Thanks again, Keith