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No codes but misfires showing under general misfire monitor

Discussion in 'SVT Shelby GT500' started by lfgt, Sep 27, 2019.

  1. lfgt

    lfgt New Member Established Member

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    I recently started using a bluetooth obd2 scanner (OBDLinkMX+) in conjunction with their app so I can see the different sensors and pids in real time (This app seems similar to Torque). There is a pid that shows 'Total Number of Misfires' and have only started looking at it the last 2 driving sessions. This afternoon it showed 6 total misfires after a quick 20 minute drive. No codes were thrown and car ran fine showing no symptoms of a misfire.

    I looked at the data under MODE $06 were you can see misfires for individual cylinders and all were clear. But under 'Misfire Monitor General Data' there was this:

    20190926_180559.jpg

    I have found this info on another forum for the id's

    Monitor ID: $a1; Test ID $80 is the "Total Engine Misfire Rate and Catalyst damage misfire rate (Updated every 200 revolutions)". This is continuously monitored by the PCM's misfire status monitor.

    Monitor ID: $a1; Test ID $81 is the "Total Engine Misfire Rate and Catalyst damage misfire rate (Updated every 1000 revolutions)". This is continuously monitored by the PCM's misfire status monitor.

    Monitor ID: $a1: Test ID $82 is the "Highest catalyst-damage misfire and catalyst damage threshold misfire rate (updated when DTC set or clears).

    Monitor ID: $a1: Test ID $83 is the "Highest emission-threshold misfire and emission threshold misfire rate (updated when DTC set or clears)

    Monitor Id: $a1: Test Id $84 is "Inferred internal catalyst mid-bed temperature" This is a calculated value - not taken from an actual sensor.

    Has anybody encountered this before?

    I am running no cats the spark plugs are fresh with probably around 1000 miles on them. The previous time I drove the car it showed 0 misfires. The only thing that has changed is the fuel. I will run this tank down and switch back to what I was using before to see if it changes.
     
  2. me32

    me32 BEASTLY SHELBY GT500 TVS Moderator

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    What kind of fuel are you running?
     
  3. lfgt

    lfgt New Member Established Member

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    I discuss my situation and fuel I run in detail in this thread:
    https://svtperformance.com/threads/...s-running-95-octane-mix-on-a-93-tune.1178473/

    In summary the car is tuned for 93 and I am now running a mix of 93 and 100. Mixed in a ratio of 1 gallon of 100 to every 4-5 gallons of 93 to raise the octane at least 1 point just out of fear of getting 93 that is not up to par.

    The 93 is from Phillips 66 and contains ethanol. The 100 is Sunoco 260 GT unleaded and also contains up to 10% ethanol.

    Before this tank I was running 95 octane that is on pump at a Harley dealership. They mix the 100 (Sunoco 260 GT) with ethanol free 91 to make 95.
     
  4. lfgt

    lfgt New Member Established Member

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    Went for another ride to get more details and the misfire count seemed to only increment when coasting or rev match down shifting. It did not seem to increment under acceleration. Short term and long term fuel trims looked good to me also.

    It was about a 30 minute drive and got a total of 6 misfires. They did not start occurring until the car was up to temp or about 10 minutes into the drive. I will go for another drive later today without doing any rev match downshifting and see if there is a correlation.
     
  5. Catmonkey

    Catmonkey I Void Warranties! Premium Member Established Member

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    If you're not getting DCTs, your PCM must not think it's a problem.
     
  6. me32

    me32 BEASTLY SHELBY GT500 TVS Moderator

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    How old is the fuel?
     
  7. lfgt

    lfgt New Member Established Member

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    2 weeks since I got it from the pump. I am only storing about a months worth of fuel so that it is not sitting around very long.

    To clarify my current filling routine I run the tank down to half then dump one of the 5 gallon jugs in the tank and repeat. Yesterday before i drove I put the 4th 5 gallon jug into the tank of the new mix. So now I have cycled nearly a full tank and I am sure it is mostly the 93 and 100 mix now in the tank.
     
    Last edited: Sep 27, 2019
  8. fullboogie

    fullboogie Well-Known Member Established Member

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    I have yet to hook up a bluetooth unit that doesn't show that misfire code. It's on my GT500, my 4Runner, and my Dodge. It's not a vehicle specific code, it's one of the general PID's. I think it just errors-out on most of these units. I would not worry about it.
     
    HKusp likes this.
  9. lfgt

    lfgt New Member Established Member

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    Thanks for the responses. As what most of you have said above I am not going to worry about it. I did a lot of driving this weekend and have come to the conclusion switching my fuel has nothing to do with it and was just coincidence. They would not occur when driving aggressively only when coasting and maintaining speed.
     

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