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Thread: Finally back to my duty cycle question, and now some misses during deceleration.

  1. #1
    Join Date
    Sep 2018
    Location
    Grand Rapids, MI
    Posts
    49

    Default Finally back to my duty cycle question, and now some misses during deceleration.

    Those of you with a good memory may recall my post about seeing my injector duty cycle going crazy high for no apparent reason. After several other projects on the car this summer, I'm back to trying to fix it. Here are the important data points:
    1966 Corvette with a 327 small block. Aluminum Brodix cylinder heads, semi-hot cam, about 10:1 compression, but running exclusively on E85. My Sniper is supposed to be good to 600 HP on pump gas, so degrading it 30% for E85 still says I should be good to 420 HP. I really don't think I'm near 420 HP.

    I datalogged data tonight and once again see blips where I'm hitting an injector duty cycle around 120% at roughly 4200 RPM! Links to my Config File and a corresponding datalog are below. The 120% duty cycle at 4200 RPM event happens around 621 seconds into the data, but there are a few other places where I exceeded 90% duty cycle without trying very hard.

    I've also noticed in the last several days that I'm experiencing some misses/hiccups during deceleration. If I'm running under normal throttle and then pull my foot completely off the accelerator while still in gear (4 speed car) and the engine winds down (like 3500 RPM, 3000 RPM, 2500 RPM, etc.) with the TPS at 0%, I'll often get a few stutters/pops that almost sound like it's backfiring through the throttle body. I was expecting to see the MAP spike in the datalog when this happens, but can't find any indication of that (at least to my untrained eye). Very much appreciate anyone that can take a few minutes to help a brother out!
    https://www.dropbox.com/s/2kyeq49iqj..._0013.dlz?dl=0
    https://www.dropbox.com/s/pe82m7pd3s...0B.sniper?dl=0

  2. #2
    Join Date
    Jan 2010
    Location
    Brisbane, Australia
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    1,443

    Default

    Interesting how you can get injector duty cycle higher than 100%.
    Regards, Gary

  3. #3

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    The data isn't correct, so then you have to try and figure out why the data isn't correct. RF noise can cause that issue by confusing the ECU. For example, I've seen situations where the ECU thinks the RPM is much higher than it actually is, or it thinks the TPS is wide open when it isn't. Then it spikes the fuel to respond.

  4. #4

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    I really can't answer anything specifically because I have zero experience with E85 and don't really understand how it works in your setup. For example, your Target AFR table uses gasoline air fuel ratios. I'm not sure how your car runs on E85 at gasoline AFRs?

    One observation that struck me in your log is that the system is constantly jumping in and out of Closed Loop. A lot of that is because it goes into Open Loop when the TPS changes and with a 4 speed that is often. Maybe take a datalog from a freeway cruise where TPS is steady and see if it is still jumping in and out of Closed Loop?

    Your actual AFR is all over the place as well. That makes sense when in Open Loop, but even in Closed Loop it appears to struggle to meet the target.

    Have you tried running gasoline in it to see what happens? It's just hard to tell if you have a problem with ECU or a sensor or if the problem is you are trying to run it on E85.

  5. #5
    Join Date
    Nov 2014
    Location
    Ont. Canada
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    1,323

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    Quote Originally Posted by gregs69rs View Post
    I really can't answer anything specifically because I have zero experience with E85 and don't really understand how it works in your setup. For example, your Target AFR table uses gasoline air fuel ratios. I'm not sure how your car runs on E85 at gasoline AFRs?
    It doesn't matter if you run on a gasoline scale. 14.7 is just a multiplier. All WBO2 sensors are based off of Lambda. Stoic for all fuels is Lambda 1. If you want to be 10% rich you would run at Lambda .9 AFR. So if the multiplier for gas it 14.7 you would multiply Lambda 1 X 14.7= 14.7 AFR. If you wanted to be 10% rich on the gasoline scale you would multiply Lambda .9 X 14.7= 13.2 AFR. If you're comfortable using the gasoline scale you can, all it means is the ECU will have to add more fuel to get to your Lambda 1 / 14.7 or 10% rich Lambda .9 / 13.2 AFR.
    Last edited by 81 TransAm; 07-13-2019 at 02:55 PM.

  6. #6
    Join Date
    Sep 2018
    Location
    Grand Rapids, MI
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    Quote Originally Posted by andyf View Post
    The data isn't correct, so then you have to try and figure out why the data isn't correct. RF noise can cause that issue by confusing the ECU. For example, I've seen situations where the ECU thinks the RPM is much higher than it actually is, or it thinks the TPS is wide open when it isn't. Then it spikes the fuel to respond.
    Any pointers for me on trying to track down a potential RF noise issue? I did see a couple examples of noise in the RPM signal during previous datalogging (nearly instantaneous blips that went from something like 4300 RPM to 6800 RPM and then back to 4300), but I wasn't able to see that in THIS dataset. Which also confuses me!

    Another thing that I keep coming back to is not enough fuel pressure. Would a drop in fuel pressure cause the erroneous duty cycle values? The fuel pump I'm using is right from the Sniper kit that includes the pump & filters, but maybe something in my fueling system isn't keeping up? My fuel lines from the tank to the engine (and the return to the tank) are 100% E85 rated "rubber" hose that I ran inside the frame rails. Is the flex line a problem with pressure drop? Thanks everyone for the feedback!

  7. #7
    Join Date
    Sep 2018
    Location
    Grand Rapids, MI
    Posts
    49

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    Quote Originally Posted by gregs69rs View Post
    I really can't answer anything specifically because I have zero experience with E85 and don't really understand how it works in your setup. For example, your Target AFR table uses gasoline air fuel ratios. I'm not sure how your car runs on E85 at gasoline AFRs?

    One observation that struck me in your log is that the system is constantly jumping in and out of Closed Loop. A lot of that is because it goes into Open Loop when the TPS changes and with a 4 speed that is often. Maybe take a datalog from a freeway cruise where TPS is steady and see if it is still jumping in and out of Closed Loop?

    Your actual AFR is all over the place as well. That makes sense when in Open Loop, but even in Closed Loop it appears to struggle to meet the target.

    Have you tried running gasoline in it to see what happens? It's just hard to tell if you have a problem with ECU or a sensor or if the problem is you are trying to run it on E85.
    It's interesting that you say the AFR is all over the place. This is my first attempt at fuel injection, so I have nothing to compare my datalog to! I've just been assuming that what I'm seeing is normal! And yes, I've noticed the constant switches from Open Loop to Closed Loop, but here again, have no other experience to say whether that's normal or not.

  8. #8
    Join Date
    Sep 2018
    Location
    Grand Rapids, MI
    Posts
    49

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    One more thing I forgot to ask above. Anyone got any pointers on how to actually MEASURE fuel pressure during actual driving situations? I have a fuel pressure gauge that I can connect into the system, but I have no clue how I'm going to be able to see and read it during hard acceleration!

  9. #9

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    If you don't have a cowl hood you can probably get a sending unit to report to the Holley dash. Otherwise you can use an -AN hose to get it under the cowl to see it.

  10. #10

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    In the datalog, if you click on the AFR line then the box at the top will display the min, max and average for that data point. Your min AFR on the run was 9.6, max was 23.9 and average was 13.8. Definitely not normal at all. At steady cruise you would probably see +-0.5 maybe? On the WOT blasts it is common to have a lean spike, but not like your datalogs.

    In terms of tracking down RF noise, the two top culprits I think are inadequate engine grounds and not using clean power for the ECU 12 volt trigger wires. A close 3rd is magnetic pickup distributors. Do you have a ground cable from the negative post directly to the engine block? How is the pink 12V trigger wire getting power?

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