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Thread: Acceleration AFR Spike - Review

  1. #11


    I have no idea about tuning ignition timing in EFI, and our engine is basically stock and N/A, but as far as fuel: No point in messing with the TPS RoC, etc until you get the Base Fuel Table dialed in, and unless you've got Closed Loop (Learning) turned off, making changes to the fuel tables won't accomplish much, as the Sniper is doing everything it can to get to whatever Target AFR you have plugged in there.

    Try (with Closed Loop ON and at least 25% CL Comp allowances) changing the Target AFR values in the relevant cells while accelerating, see what effect that has - I could definitely feel when ours was too lean and then rich under light acceleration, and I then set the Target AFRs in the middle (with leaner cruise and richer hard acceleration Targets). Having a buddy helping with the laptop or driving really helps (you can do 90% of the tuning on public roads, driving legally.)

    For example: Using a laptop, Closed Loop and Learn "on", and either datalogging or the Strip Chart turned on so you can see the "bubble" in the Config tables, start out at steady 2500 RPM and say 45 kPa, change the Target AFR to leaner and richer and see how the engine responds by feel and watching the kPa (looking for a nice steady reading). Once you find the steadiest kPa and leanest (that you dare) Target AFR, that's going to be a "Cruise AFR". Then starting at 2500 RPM and opening the throttle to accelerate, you'll see the kPa jump up to maybe 60, and the engine goes lean - so change the Target AFR in the 2500 RPM/60 kPa cell(s) to something richer, and try it again - until you find the sweet spot. Repeat all that for different RPM and rates of acceleration, like every 500 RPM up and down the scale and modulating the throttle to get the 'bubble' to say 80, 100, then boosted kPa values, and you'll build yourself a really good Target AFR table - which the Sniper will then use its learning ability to achieve. Then you can go in, transfer the Learn Table to the Base Table, and smooth it out. Basically you're making it easier for the Sniper to make it's calculations, plus you'll get a Base Fuel map that will work just as well in Open Loop as Closed Loop. Once you find the Target AFRs your engine likes, then you can mess around with the Acceleration Enrichment values - we found that the default settings were fine, once we dialed in the Target AFRs.
    Last edited by bruzerbruce; 12-03-2019 at 07:46 PM.

  2. #12


    Thank you for the input. I'll need a dyno to do tuning this in depth. I did some more cruising and got more datalogging done. I will review the datalog and Config File and post it up shortly. I had more lean spikes and one jumped to 17.4, but it seemed to adjust after that with more driving. I talked to a few tuners at the local car show and got some more advice to try for my setup. They did repeat quite a bit I've read on here from all of you. Still comes down to reading the plugs and seeing what it likes. More to follow shortly.

    I attached the datalogs and config file. I made some "experimental" changes and took a datalog of some random accelerations to see what everything does.
    I did notice some slight popping out of the exhaust while accelerating a little harder when I approached boost so I adjusted timing and fuel slightly to lean it up a little.

    I'm slowly adding timing and pulling fuel until they agree. I made the timing changes to the cruising RPM ranges and it made a big difference. For this Config File I will do a long cruise on some open back roads, so I can get some consistent datalogs to view as changes to the Learn Table are made. Thanks again for all of the input. If someone learns from this then my struggles are well worth it.

    Disregard the Config File. I just realized all of the fuel and timing pressure axes were changed to 16 psi & -11 instead of where I had them before. I'm resetting to 12 PSIG & -9 and redoing both tables. Not sure when this occurred, but it explains why it did not feel right today. Attached is the revised Config File. I'll adjust more after tomorrow's driving & datalogging.
    Attached Files Attached Files

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