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Thread: Unburned fuel in exhaust due to cam

  1. #1
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    Unburned fuel in exhaust due to cam

    I have an Lq4/4l60e with 243 heads and a gm hotcam with 1.5 extra degrees of LSA.
    I finally realized that my troubles while trying to tune my VE table are from unburned fuel in the exhaust from the cam overlap (i assume at least).
    I finally richened the lower rpm area (via VE table) way more than the 02 sensors wanted and it got rid of the terrible lean stumble i was having from a stop.
    Now it is driving wayyyy better but wants to die at idle in gear. I think it just needs the VE tuned in that area.

    My question is: is there any better way to dial in the VE other than guessing and checking. since i can not rely on the O2 sensors at low rpms apparently.
    Maybe somehow match my VE to what the maf reads or something?

    richen idle gear 1.hpt

    wont idle in gear.hpl

  2. #2
    Senior Tuner cobaltssoverbooster's Avatar
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    have you tried researching End Of Injection Timing (EOIT)?
    this is something people with cams tend to research as it can adjust some of the blow through on the fuel side that is caused by cam overlap greater than the factory cam designs.
    2000 Ford Mustang - Top Sportsman

  3. #3
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    I hadn't until just now. It sounds like it could help the problem. Ill definitely give it a shot with small increments of .5 or 1..? Couldn't find specifics on how much to change. Thankyou!

  4. #4
    Tuning Addict 5FDP's Avatar
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    If you haven't been using a wideband to tune, how do you even know it's running good?

    You should never just guess and check while tuning the VE.

    You also do not want to log the MAF while tuning the VE, it can skew data.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  5. #5
    Senior Tuner cobaltssoverbooster's Avatar
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    increasing the value by .11 pushes the injector operation back and since the exhaust happens before the intake, retarding the event sprays the fuel closer to the intake side which prevents less fuel from going into the exhaust on overlap. If i remember right an injection period is 90* and .11 comes out to roughly 10* of injector shift.
    2000 Ford Mustang - Top Sportsman

  6. #6
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    I would get a wideband but would it not read way richer as well since there is unburned fuel in the exhaust from the cam? and that was my mistake. I have been logging without the maf. i had just added it back in to check what it was reading and forgot to stop logging it for that run. But the results have been the same without it being logged (reading way richer than should)

  7. #7
    Tuning Addict 5FDP's Avatar
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    A wideband is a tuning tool, you need it to properly correct your fueling. For sure WOT tuning it's a must.

    Not having one is kinda like shooting yourself in the foot.

    Your camshaft is not very aggressive at all, in fact it's pretty mild compared to others. You can totally fine tune the motor to run that cam but you will need a wideband to help you.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  8. #8
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    Ive also been slowly increasing the injection timing by .11 with no luck. Still stays rich

  9. #9
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    i was definitely planning on getting a wideband when i got to WOT tunning, but just barely accelerating from a stop it falls on its face and will die. I can go ahead and get one for the early on stuff but will that help with this issue? It seems to be going lean opposite of what the narrow bands think, because if i richen it via the AFR tool in the scanner, it will accelerate from a stop just fine.