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Thread: E38 Randomly +20% Rich

  1. #1

    E38 Randomly +20% Rich

    I'm having a issue with my turbo 5.3 getting -20% fuel trims all of a sudden. I have not done any flashes lately but I feel like its possibly tune related. I haven't got my VE or MAF as dialed in as I would like it because I'm fixing to do some changes to the fuel system but my STFT have never varied by much and the truck drove fine. I've had this happen in the past and I was able to fix it by just doing a " write entire" on the PCM but why??? Is it time for a new PCM? I'll try doing a write entire in the AM again to see if that fixes the issue. As far as it being a mechanical issue, I don't notice any issues. Its not throwing any codes, it doesn't feel like its missing, doesn't run rough, fuel pressure is constant and logs seem pretty normal besides the fuel trims. When trying to go WOT, its definitely pig rich and therefor the motor is bogging down as where before this was never a issue. I'm just a little confused as to why this would happen all of a sudden?

  2. #2
    Log and tune files?

  3. #3
    Quote Originally Posted by wildfan1976 View Post
    Log and tune files?
    Oops

    Current Tune.hptRich 2.hpl

  4. #4
    So I did a "write entire" today to see if it would fix the issue and it did. I'm not sure why it would randomly one day start needing to pull 20% fuel to get to stoich and how doing a "write entire" of the same exact tune would miraculously fix the issue but it did. The truck went from having -20% fuel trims and being pig rich during power enrichment (I saw 9's on the WB) back to having +4% fuel trims and power enrichment afr's being back into the 11's..........WEIRD

  5. #5
    So I flashed the truck last night and all was well. I drove it this morning to work and everything seemed fine and my STFTs were where they should be but when I drove it home it was back to acting up again. I noticed my wideband occasionally dipping down into the 12's under normal driving (this is how I know its doing it again) and I only notice this happening when coming off the gas (like coasting to a stop light). Once I noticed this, I plugged in the laptop to see what the STFT's were and of course they were reading close to -20% again. Any clues guys? If you look at 00:03:52 on the Rich 2 log I uploaded, you can see the dip in the wideband that I am referring to.

  6. #6
    Just looked at your injector data and your flow vs pressure is not right at all. What kind and size of injectors are they?

  7. #7
    Quote Originally Posted by wildfan1976 View Post
    Just looked at your injector data and your flow vs pressure is not right at all. What kind and size of injectors are they?
    I should have probably mentioned that it is a return-style fuel system with a boost referenced fuel pressure regulator and the fuel pressure control module has been removed. They are Fuel Injection Connection injectors and they are rated at 114 LB/H at 58 PSI.

  8. #8
    Senior Tuner
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    are the injectors ur using designed for e85 ? stainless internals ?

  9. #9
    Quote Originally Posted by 07GTS View Post
    are the injectors ur using designed for e85 ? stainless internals ?
    They are.

  10. #10
    So I drove the truck again today. I stopped at a gas station to re-flash the truck and I took a before and after log. There is clearly a good 20% difference in STFT's before and after the re-flash of the exact same tune. I'm lost.......Rich 6.hplRich 7.hpl

  11. #11
    Advanced Tuner
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    Interesting calibration - a 2011 Truck, running a 2012 E38 OS, upgraded to an HPT COS.

    What type of fuel are you using ?

    Do you always fill the tank with the same grade / type of fuel ?

  12. #12
    Log your Intake Valve Temp and see what its at when it does this.

  13. #13
    Quote Originally Posted by Jon S. View Post
    Interesting calibration - a 2011 Truck, running a 2012 E38 OS, upgraded to an HPT COS.

    What type of fuel are you using ?

    Do you always fill the tank with the same grade / type of fuel ?
    Yup. My operation system didn't have the 2 bar SD option and I was tired of messing with the VVE. I could never get that thing to do what I wanted so I found a OS that was supposedly compatible with my PCM, transferred all of my data of and did a "Write Entire". The new operation system had some tables that my original didn't and I just left them as stock. I normally stick with e85 from my local gas station but I'll occasionally fill it up with a tank of 93.

  14. #14
    Quote Originally Posted by wildfan1976 View Post
    Log your Intake Valve Temp and see what its at when it does this.
    Will do. I haven't seen it start pulling a ton of fuel yet but as soon as it does, I'll post a log.

  15. #15
    Also, here is a copy of a older tune of mine when I had a shop tune it. This was running the older operation system if you wanted to compare the two tunes and see the differences between the two. I know there is some additional tables in the O2 section and the alcohol content scaling was a little different between the two. ATTACH]105344[/ATTACH]
    Attached Files Attached Files

  16. #16
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    Quote Originally Posted by TAPyvehc93 View Post
    ... I normally stick with e85 from my local gas station but I'll occasionally fill it up with a tank of 93...

    The 2010+ E38 operating systems had issues with the "virtual" Flex Fuel Sensor algorithm, which often caused the commanded AFR to be incorrect for the type of fuel in use - these generally command an overly rich AFR.

    Problem trucks often had the rear bumper / tailgate covered in black soot, from the overly rich AFR being commanded. If memory serves, there was a GM Service Bulletin on this topic.

    If you always use the same fuel type / grade, then you can setup your calibration for that fuel type solely - which eliminates the random AFR swings caused by the virtual flex fuel sensor (if that is your issue - it certain sounds like it may be the case).

  17. #17
    Quote Originally Posted by Jon S. View Post
    The 2010+ E38 operating systems had issues with the "virtual" Flex Fuel Sensor algorithm, which often caused the commanded AFR to be incorrect for the type of fuel in use - these generally command an overly rich AFR.

    Problem trucks often had the rear bumper / tailgate covered in black soot, from the overly rich AFR being commanded. If memory serves, there was a GM Service Bulletin on this topic.

    If you always use the same fuel type / grade, then you can setup your calibration for that fuel type solely - which eliminates the random AFR swings caused by the virtual flex fuel sensor (if that is your issue - it certain sounds like it may be the case).
    I've actually wired in a ethanol sensor so the virtual sensor has been disabled.

  18. #18
    Your ambient air temp is 32 in one log and 60 in the other.