Sputtering at beginning of WOT

Discussion in 'Forced Induction - 5.0L V8 Engine' started by convertix, Jun 12, 2019 at 8:42 AM.

  1. convertix

    convertix Member

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    Hey Everyone,

    I'm at my wits end on this. Here are my mods that are relevant to this post:

    2015 Mustang GT
    Roush Supercharger
    E85
    72mm upper
    5%OD ATI Damper
    SAI LI Fuel System
    DW 95 Injectors
    VMP Fuel Rails
    VMP Tune
    JLT 123 CAI

    I've been trying to nail down an issue with the car sputtering for a quick second and then it takes off like a beast. I've logged the car several times. I'm not an expert of looking at the logs but I have gotten familiar with them enough to notice a few things. To me, it seems like I'm running rich when I'm doing a slow rev in 4th gear and then go WOT around 4500rpm when it will sputter for a quick second and then take off.

    I was having knock (around 4.00), which VMP thought it was false knock and asked me to look if the exhaust was hitting anything. I've been tracking down knock for weeks.

    One day I was reading some articles and noticed that everyone that was using the SAI Li system was using the Purple/Green wire and I was using the Yellow/Grey wire on the wiring harness. The difference is the Purple/Green wire primes the pumps continously and the Yellow/Grey wire primes like stock. When I switched to use the Purple/Green wire it ran almost perfect, but still had sputter when going WOT, but wasn't NEAR as bad. AND all of the positive knock went away and I finally started getting negative knock!

    Yesterday, I thought that maybe my problem was that I didn't have a boost reference hose hooked up to the fuel regulator, so I got the parts I needed and hooked one up. I set a baseline of 55psi (per VMP). I took the car around the block and the car ran much worse with the boost reference ON.

    I can't figure out what that happens. Perhaps my fuel pressure is dropping when the engine is hot? Any thoughts would be appreciated.

    The Fuel System can handle 950whp on E85 all day long, so it's not that. Thanks in advance!
     
  2. Tommy V

    Tommy V Well-Known Member

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    If you hooked a boost reference up and it ran worse you are running to rich.The boost reference adds fuel pressure as boost rises.What is measured a/f during a 3rd gear pull.You should be .78 and maybe as low as .75 but any richer could cause issues.
     
  3. OP
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    convertix

    convertix Member

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    I've had numbers as low as .81 during a slow rev while in 4th gear. Is this a tuning issue? Is the fuel pressure too high?
     
  4. Tommy V

    Tommy V Well-Known Member

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    If .81 was low,no thats not rich.What was tbe highest you seen especially at higher rpms?.You want your a/f to be around .78 to .80 all the way through the pull.The higher the number the leaner you are,lower your are its richer.
     
  5. OP
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    convertix

    convertix Member

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    I'm talking about fuel trims with that number. Perfect is supposed to be 1.0. I've seen the trims be anywhere from .81 to 1.04. Once the car get past the little sputter and takes off, it's usually around 1.0+-. I just took a data log. I'll look that over. I adjusted the fuel pressure back to baseline of 55psi and took it out. Better than yesterday. Wish I could figure this out. Frustrating
     
  6. Tommy V

    Tommy V Well-Known Member

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    If you see fuel trims of .81 during wot pull you have problems,very rich.What does your tuner say.It could be a bunch of stuff,maf curve wrong,or mechanical.Compare your a/f to your fuel trims as the rpms rise through the pull.
     
  7. OP
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    convertix

    convertix Member

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    Looking st the log, actual WOT is in the low 90s throughout. Still rich imho. It takes a long time for the tuner to get back. Sometimes can take 1.5 weeks! One thing is for sure is the car is running better than yesterday, but still not good enough. The only thing I changed was readjust the baseline on the regulator. Appreciate your help.
     
  8. rANDIANDI

    rANDIANDI Cashfed5.0

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    literally had this same issue around 4000-4500 the car would leave and than kinda stutter and than take off again.

    i traced mine down to spark plugs, i would pull them and check the gap and replace them with new ones.
     
  9. Tommy V

    Tommy V Well-Known Member

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    Not the plugs would miss at high rpm and boost also.What you could try is lower your base fuel pressure down to 53 or 52 and see if your fuel.trims come down a little bit.Just make sure you look at the upper rpm limit to make sure your a/f ratio is still good.
     
  10. OP
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    convertix

    convertix Member

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    I thought about doing that too. I'll try that later today and post the results.
     
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  11. hossman

    hossman Well-Known Member

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    I am having the same issue and was told it could be spark blowout after looking at the datalogs and explaining what’s intermittently happening. I just had new Brisk plugs installed and was informed they have been seeing some blowout lately with them and I was told to put in NGK6510’s. Once I put them in I’ll let you know if it fixed the issue.
     
  12. OP
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    convertix

    convertix Member

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    I was told the same thing. So I went out and bought new 6510s about 2 weeks ago. I dont think it made a difference in my case. But I hope that fixes your issue though.
     
  13. Tommy V

    Tommy V Well-Known Member

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    Spark.blowout usually happens at the upper rpms and boost.His car breaks up at 4k then is fine all the way to redline!!!,this is not spark blowout or pkugs period.
     
  14. whatsup62

    whatsup62 Well-Known Member

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    Really? How do you know this? Are you running the standard Sai Li system or his new upgraded one?
    I am Procharged so it may not be Apples to Apples but my Sai Li system was starting to lean out around 14psi with ID1000's @800rwhp on E85 so ended up installing a Fore system.
    Who is your tuner? They should be able to identify the issue and instruct you on how to set the regulator.
    Im Lund tuned and again this might not be apples to apples but this was how Jon instructed me to set the regulator on the Sai Li kit.
    "I want the base fuel pressure set to 58 psi with the engine running and the manifold reference off the regulator. Once set, leave the reference off and let the regulator reference atmosphere, so don't cap the nipple on the regulator."
    Never had an issue until switching to the D1X looking for more power.
     
  15. OP
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    convertix

    convertix Member

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    Yes, the SAI LI system is the new one. I just got it a month ago. The car is running rich for sure. VMP is my tuner. I've reached out to them but it takes forever to get a response if you didnt pay for expedited service, which I didnt. Now I wish I had. But thank you for your advice with the Lund verbiage. VMP is almost the same except base psi is 55 instead of 58.

    Your car sounds like a beast! I've heard great things about the D1X.
     
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