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  • Datalog Feedback

    We've been experiencing issues while the car is under a load and trying to identify potential issues. We had issues after the latest ECU firmware/EFI software update, but we reverted back to the previous versions. While things have improved we're now having issues with the car under load (breaks up and erratic RPM). I had the RPM signal wire from the CDI box connected to the shift light and tach, but have separated those to have a cleaner tach signal to the Sniper. The engine is a bone stock 351W.

    One thing I've noticed is the throttle linkage seems to stick (we replaced the accelerator cable) and idle RPM are above the 750 target. The attached datalog is at idle. I've also attached the current GCF that's on the car. I realize it's a very short datalog, but would appreciate any input.
    Attached Files

  • #2
    See this thread regarding idle issues:

    If the engine is bone stock why was a Street/Strip cam selected when creating the Config File. When you go above a Stock cam, the system automatically fattens up a number of parameters. Given that you have an idle kPa of about 29 it would seem that you have a stock or very mild cam. 29 kPa translates to a vacuum of about 22 inches of mercury. Since the tune is very basic you may want to generate a new Config File with the Wizard and select a stock cam.

    The Config File shows pretty rich Target AFR values for a stock engine. An overly rich mixture can cause higher RPM issues in some cases. In your existing setup if you use the EFI software change the idle AFR to 13.9, cruise to 14.4 and WOT to 12.9. Than, in the software, change "Simple" to 2D Table to allow further tuning refinement in the future.

    The unknown variable is timing and ignition. On stock engines there's a tendency to change plug gaps due to the information provided in the MSD instructions. Opening the gap to .045" or more may lead to misfires in some applications. The easiest way to tell is to take your plugs back to stock, maybe .035" depending on the engine and heads. When troubleshooting you need to try some things. If 0.035" doesn't make it better at least you know that it wasn't the plug gap.

    Since the Sniper isn't controlling timing, we have no idea where you have set your timing and what timing curve is being used. You may want to back the timing off by 5 and testing and then go 5 more than where you started and see what you end up with.

    Even with light throttle input your TPS RoC values are high and this is kicking you out of Closed Loop. If your throttle is sticking it may cause your TPS to jump very quickly and this may create an unnatural condition that causes the Sniper to go to Open Loop. When it does this you end up with a AFR oscillation and when it goes back to Closed Loop it loses its mind for a few seconds. Try a datalog with slightly slower throttle input to see if tracks better. You may need a throttle lever extension to slow the rate of throttle input down, or you may need a little stiffer throttle spring.


    • #3
      Thanks for the review and input. I neglected to mention the tune that is being used is from our previous engine that had a mild cam and different heads. We ran this tune at our last endurance race without noticeable issues. The plugs are gapped to 0.045". I’m sure the previous heads flowed better which allowed for more fuel, but with more restrictive flowing heads the tune is now rich. The plugs all look the same with coloring pointing to a lean condition vs rich.

      We’ll close the plug gap, adjust the linkage and idle setting, then start a new tune using the Wizard and see how it goes.


      • #4
        Forgot to mention that in datalog 0003 your battery voltage is running a pretty constant 12.2 volts. The Sniper, ignition components, and fuel pump are often not happy at low voltage levels. Is your alternator active? The battery voltage displayed in datalogs comes from the pink ignition trigger wire. If you have the pink wire connected to the ignition switch directly there may be other loads on the system.


        • #5
          We started with a fresh Wizard base tune, checked plug gaps, adjusted timing to 12 BTDC and took the car out for some testing. The car does break up a little around 4700, but it is better. That said I'm not sure what adjustments to make next. Any input would be appreciated.
          Attached Files


          • #6
            This tune is not terrible, but it needs work. The added fuel in the Learn Table in the idle area seems appropriate for a stock cam engine. It was breaking up at 4700 RPM because it was rich. I would also consider rescaling the RPM axis, because this engine is never going to see 7000 RPM, so you may as well use as much of the VE% Table as possible.

            The other thing I noticed is that at hot idle, the IAC is closed, timing is being retarded, and the engine can't idle down. This means that the throttle blades need to be adjusted to achieve proper IAC Position values at hot idle.

            If I can help with the tuning, please email me: projectgattago at gmail dot com. Andrew
            Instagram: @projectgattago
            Offering remote Holley EFI tuning.
            I deliver what EFI promises.
            Please get in touch if I can be of service.


            • #7
              Thanks for the input Andrew. Obviously, I’m not well versed in tuning and will send you an email. As GPatrick mentioned above, I have the pink trigger wire sharing a connection with at least one other 12V source, so I probably need to move this.