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Thread: Very rich decel after PE

  1. #1

    Very rich decel after PE

    Hello guys.

    I've tried searching and didn't come up with much on this issue.

    I recently did a lot of work to my 2003 c5z. It has AFR heads, slp 1.85 rockers, K&N intake, GTP/ASA injectors, ported throttle body, ls7 exhaust manifolds and cats and 3" xpipe. Injector data I got from this forum and it should be the GM specs. I have since lowered my min pulse widths to .897 from 1.277. This seemed to help in some areas, but it did not help my very rich condition.

    I am having an issue with very rich decel. My AFR gauge will peg itself on 10:1 at times. This does not seem to be an injector data issue to me anymore. It appears like the fuel is being commanded.

    In the log there are two instances of this happening. First is around frame 2600. Next is about 3200. Both times are after power enrichment kicked in. The first time it took 15 seconds! to recover. Second time DFCO kicked in which is about the only thing saving me from this issue.

    I've attached my tune and a log showing the issue.

    Any help or feedback is greatly appreciated!

    Thanks,
    Daniel
    Attached Files Attached Files
    Last edited by dankmac; 08-22-2014 at 11:53 AM.

  2. #2
    Any suggestions?

    Thanks.

  3. #3
    Advanced Tuner Ranger6202's Avatar
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    Have you calibrated your Maf or VE yet?

  4. #4
    Advanced Tuner Ranger6202's Avatar
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    i'm not a genius with injectors yet. But i noticed that even at 5k + RPM's you're duty cycle is only 8% tops. What size injectors are you running?

  5. #5
    Quote Originally Posted by Ranger6202 View Post
    i'm not a genius with injectors yet. But i noticed that even at 5k + RPM's you're duty cycle is only 8% tops. What size injectors are you running?
    Are you talking at wot? It should be high 60s or low 70% duty cycle. They flow 42 lb/hr at 58psi. They are injectors from the GTP.

    I haven't touched the VE table, but I have done a lot of maf tuning cycles. It averages +/- 3% on the STFTs

  6. #6
    Advanced Tuner Ranger6202's Avatar
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    went back through it....my bad, it was around ~60% @ 4000 RPM. I did notice though that Commanded AFR goes straight to 14.68 as soon as you let off. WB's go rich....tells me you have residual fuel or heavy film on your valves (TAU) from the enrichment period. OR it might be the CAT over temp protection crap. In your tune your STFT's and LTFT's are disabled but you still have STFT's. Might want to reset those just to clean things up and start with a clean slate. Start with disabling the cat over temp, and then i have a few more ideas if that don't work.

  7. #7
    The car is definitely running closed loop with stft enabled. Ltft are turned off.

    Cat over temp is an interesting idea. I'll have to give that a try.

    I'm on a business trip the next couple days so I'll have to try over the weekend.

    Both the wbo2 and narrow band o2s show it goes way rich. It is commanding stoich, but it is getting lots of fuel from somewhere. I know the injectors aren't too large or set up incorrectly. It has no issues following stoich in every other condition.

    I have noticed that the duty cycle is a hair higher when it is rich.

    It seems like to me that something is overriding the fuel trim's ability to command the injectors?

  8. #8
    Advanced Tuner JamesLinder's Avatar
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    Slopping Programming

    Why have you changed torque to enable power-enrichment to 100%? This may be causing your unintended problem
    with enrichment after engaging PE, preventing PE from being disabled, not sure. Attach a copy of the stock file for
    your specific vehicle so I may use it for comparison purposes; it looks like you have jacked with a lot of tables which
    should have been left stock. A lot of folks that buy HP Tuners end up changing parameters in tables that should be
    left at the factory settings. If you cannot clearly explain WHY you are changing a table value and what this change is
    supposed to do to improve performance, then always leave the GM value in the table. GM did a lot of research and
    trial and error to find out what works best for each PCM and motor combination and most of tables should not be
    changed. MAF, VE, timing, and idle tables will take care of almost everything with a few exceptions. And, unless you
    have a proven source for your injector settings, I doubt you have the right values in the program. Please post the
    modification you have made so I can determine what you should be leaving stock. And, post a copy of whatever paperwork
    you have on the injectors.

    If you have input the correct MAF and VE settings, then your power enrichment mode would be way too rich when it engages
    because your EQ ratio in the PE table are too high.
    Last edited by JamesLinder; 08-27-2014 at 01:34 PM. Reason: Add more information

  9. #9
    Quote Originally Posted by JamesLinder View Post
    Why have you changed torque to enable power-enrichment to 100%? This may be causing your unintended problem
    with enrichment after engaging PE, preventing PE from being disabled, not sure. Attach a copy of the stock file for
    your specific vehicle so I may use it for comparison purposes; it looks like you have jacked with a lot of tables which
    should have been left stock. A lot of folks that buy HP Tuners end up changing parameters in tables that should be
    left at the factory settings. If you cannot clearly explain WHY you are changing a table value and what this change is
    supposed to do to improve performance, then always leave the GM value in the table. GM did a lot of research and
    trial and error to find out what works best for each PCM and motor combination and most of tables should not be
    changed. MAF, VE, timing, and idle tables will take care of almost everything with a few exceptions. And, unless you
    have a proven source for your injector settings, I doubt you have the right values in the program. Please post the
    modification you have made so I can determine what you should be leaving stock. And, post a copy of whatever paperwork
    you have on the injectors.

    If you have input the correct MAF and VE settings, then your power enrichment mode would be way too rich when it engages
    because your EQ ratio in the PE table are too high.
    Haha please don't show my tune to GM they might cancel the tier 1 supplier contract my company has with them XD

    Seriously though, I don't think I've changed anything irresponsibly. I attached the tune I had in the car before I did the mods. Not 100% stock, but I never changed anything beyond like fan temperatures and CAGS.

    The injector data is GM data which is in the sticky on this forum. I did change the min injector pulse and default pulse width to be 30% less across the board when I was having this issue. Did not resolve my rich decel issue, but did improve fueling elsewhere.

    That is the stock torque % to engage PE.

    You can see in the log that the commanded AFR is going back to stoich 14.7 immediately after lifting off the gas. There is no delay in exiting PE.

    I changed the EQ ratio to add more fuel in PE based on my wideband. Is this not the correct method? I am at 12.5 across the RPM range on the gauge. HPTuners is reading leaner than actual.

    before head swap.hpt

  10. #10
    Advanced Tuner JamesLinder's Avatar
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    I had just seen zero % to engage PE in a few stock files that look similar to yours, but I have not tuned a car with your
    specific PCM; this is a huge difference though.

    Your PE EQ is commanding an AFR of 11.3 at WOT. If your MAF and VEs were calibrated correctly you would not be
    getting 12.5, although I agree that 12.5 is a good choice to be on the safe side. I believe that your motor must be
    too lean when in non-PE mode; are you seeing positive STFTs when you are in non-PE mode, maybe between 7% and
    8%? 12.7 to 12.9 is ideal for an LS motor, however 12.5 will ensure longevity if you are running stock pistons and rings.

  11. #11
    Without dyno testing I don't want to go leaner.

    My stft average +/- 3%

    I got there by tuning my maf. It used to be +25% on ltft with the stock tune and k&n intake.

  12. #12
    Advanced Tuner Ranger6202's Avatar
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    That should help quite a bit!

  13. #13
    Advanced Tuner JamesLinder's Avatar
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    I have found that you can go back to closed loop with LTFT enabled if you multiply the integrator delays by 1.25
    for long tube headers with the stock oxygen sensors in the collector. Even your STFTs will be more accurate.
    This increase in integrator delay by 25% accounts for the fact that the oxygen sensor is located further from
    the exhaust valve in your headers than for stock manifold. When I made this change after dialing in my
    MAF and VEs with wide band, the LTFT keeps the AFR at stoichmetric 99% of the time.

  14. #14
    That's an interesting idea. I'm using OEM c6z exhaust manifolds. I wonder if I should compare the PID values from a C6Z tune wtih my C5 and see what the differences are.

    Overall the car is running very well. The only complaint I've got is this very rich decel condition. Going to try disabling cat over temp and see if anything changes.

    If I have time on Sunday I will start working on my VE table. I want to get the tune working correctly even though the car is driving properly.

  15. #15
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    I'm still learning myself and I'm on an SD 2bar doing VE tuning. Your AFR Err% at low MAP is high. Possible the MAF isn't calibrated correctly on the low end of the scale?
    rich-decel.JPG

    PS Your DFCO temp is quite a bit higher than mine too, but the rich condition occurs > your DFCO temp so I don't think that's it. FWIW mine is set to 86*.

  16. #16
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    Hey man did you ever figure out the problem with the rich decel? I have this problem with my supercharged Jeep srt8 and the problem sounds identical.