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Thread: 1.4 E78 - Another story about knock

  1. #1
    Tuner in Training
    Join Date
    Jun 2022

    1.4T E78 - Another story about knock

    I'm tuning a 2017 Opel Corsa E running a 1.4T LUV/LUJ engine and E78 ECM.
    The car is 100% stock except a flex fuel sensor and a wideband.

    I can't get rid of the knock retard I'm seeing everytime at WOT (and less but also at part throttle for no reason), no matter how much timing I pull or how much fuel I add though power enrichment.
    Please note that I'm running 100% E85 (at the moment, ethanol concentration varies from 60% to 64%) so my guess was that I wouldn't have as much knock problems as other people running gas but I was wrong it seems...

    What's the next actions I can take to solve my knock issue?
    Could it be related to a mechanical problem of some sort? The car seems to run great otherwise, no faults or other obvious problems.
    I thought about switching to colder spark plugs (BKR7EIX) but I'm not sure if it can be of any help. Plus, I'm running E85 and from what I read it could cause issue with cold starts and all.

    I attached the tune I'm currently running and some logs at the end of the post. If you prefer, I took screenshots of the areas with the worst knock:
    2023-01-31 11_18_05-Window.png
    2023-01-31 11_18_30-Window.png
    2023-01-31 11_18_50-Window.png
    2023-01-31 11_19_11-Window.png
    2023-01-31 11_20_28-Window.png
    2023-01-31 11_20_51-Window.png

    You will notice that sometimes I'm seeing 5-6? of KR and sometimes it's close to 0 e so it's not consistent
    Also, you'll see that I tried to retard my timing a lot in the areas I was seeing knock but not with great success

    It's running MAF open loop since I'm still in the process of tuning it. MAF is dialed in and SD is next, but I would prefer to get rid of this KR issue before.
    Thanks for the help!
    Attached Files Attached Files
    Last edited by Spcbrn; 01-31-2023 at 05:00 AM.

  2. #2
    Advanced Tuner
    Join Date
    Aug 2016
    OE knock sensor control strategies can vary wildly. The fact the ECU is reporting knock retard isn't as interesting as whether this is causing the knock factor to bias towards low octane. If you're going to concern yourself with this, you should get a set of knock headphones and determine if it's real knock or not.

  3. #3
    Tuner in Training
    Join Date
    Dec 2019
    Most likely false knock. The 1.4 has fairly noisy valvetrain. The lash adjusters in them definitely leave something to be desired. My Cruze started doing the same and in my case it's definitely a lash adjuster. When I do a cam and valvespring swap in the spring I'll change the one not holding pressure well.

  4. #4
    Check your PCV rubber nipple in the intake manifold, and check the breather hose on the turbocharger. Disconnect the intercooler cold side piping and check for oil contamination inside.

    When was the oil last changed?

    Excess oil in the PCV vapors going into the intake will cause knock.

  5. #5
    Join Date
    Feb 2019
    Lodi, CA
    Plus one to every single answer on here. In my particular case when I start having knock it was 100% well not 100% but like 95% of the knock in my car was picking up was from the drivetrain and just other random things clunking around in there. One of them was the brake lines that run along the firewall between the back of the engine and the firewall right in the middle. I'm sorry not brake lines I want to say their fuel and evapor or something anyway there's some metal lines that run right down the middle where the PCV hose connects to the intake manifold on the firewall you can't miss them all it took was just a small little tug to fit I forget what I put back there like some soft like foam something and eventually I just got in there and I shimmed it out and bent the pipe ever so slightly to stop it from like vibrating against it but that and then I did have to go in and desensitize my knock sensors ever so slightly. But I do pick up knock if I go to aggressive on my car but now I don't pick it up like you're picking it up. I did have it like you though where it was just picking up shit left and right. A good way to tell if it's real knock or false knock is to add an octane booster. So you should be running at least 91 or 93 if it's available in your state. If you up the octane by like mixing a little bit of like flex fuel in there like go to a flex fuel pump and add a gallon to a full gallon or add a couple gallons to a couple gallons and you know mix them so you bump your ethanol content up and if the knot goes away that's how you know you're having real knock or at least one way to tell that you're having real knock. It's something to try anyway and it's a good quick and dirty way to you know test if what you're seeing is actually happening
    "Insert some inspirational or smart*** quote here..." - Some Dude

  6. #6
    Tuner in Training
    Join Date
    Jun 2022
    Thanks everyone for the answers!
    I will take a look at the air piping and check if there's too much oil in there. Last oil change was done 6000kms ago (or 3800miles) with dexos1 gen2 oil.

    I will also check around to see if there's anything that could cause rattle or vibration under the hood.
    @RoninDusette I'm seeing this level of knock running E85 (since it's winter it's actually around 62-65% ethanol). Since ethanol is already good against knock, should I add an octane booster anyway? Or does it simply means that what is being reported is false knock?
    And for the knock sensor levels, do you have any numbers to recommand I could start with? Thanks!

  7. #7

    You are most definitely not getting false knock here. The cause is some sort of mechanical issue. At this amount of boost even with RON 100 fuel (0% ethanol), you can get away with at least 4 to 5 degrees of timing.
    False knock usually shows up as about 2 degrees of knock retard at max and usually does not repeat at the same RPM in back-to-back pulls, but it's more random. And especially above 5500 RPM with stock valve springs.



    This is what mine looks like with RON 100 fuel and 1.5 bar of boost. The knock retard is 2.8 degrees max, and happens at 7000 RPM with stock springs and camshaft.
    The timing tapers down from 5 degrees to 2.5 degrees at max boost max rpm.

    EDIT 2:

    Before even thinking about changing the knock sensor sensitivity, i would get some sort of knock headphones. The ones you can make yourself for 20 bucks are still better than nothing.
    Last edited by sbarisic; 02-06-2023 at 07:43 AM.

  8. #8
    Do NOT just crank the thresholds attempting to get 0 reported KR.

    You actually need to run it richer - 0.80 Lambda is not enough for sustained 100% wastegate DC even on ethanol. The 1.4L LUV gets incredibly hot and is notorious for cracking wastegate housings.
    Take a look at the Sonic RS's calibration that I posted for reference. GM floods it with fuel under full load.

    Consider installing water injection, upgrading the intercooler, or both.
    The factory ignition system struggles with ethanol under heavy enrichment. BNR sells LS coil brackets - simply bolt them up and copy/paste the ignition parameters from any LS equipped truck or camaro.

    The way you can prevent knock protection from holding back boost while at the same time protecting the engine is to set the knock recovery rate very high - as GM did for the Sonic RS.
    I also max out the knock threshold at 0.1 airmass, since this is a noisy engine (and is what GM did for the 2015 Cruze).
    You can also refer to a 2011 Cruze calibration's knock thresholds which were slightly higher.
    Attached Files Attached Files