Disabling cold start?

Discussion in 'Mazdaspeed 3/6 Engine' started by jsilva, Feb 9, 2024.

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  1. jsilva

    jsilva Silver Member

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    I have read elsewhere on the internet about disabling cold start by holding the accelerator at 5% when starting the car. I tried it this morning but not sure it accomplished anything.

    Does anyone know anything about this?

    I’m not looking to always disable cold starts. I just have a cold start misfire issue I can’t solve and I really need to get my car inspected and can’t have the CEL come on.
     
  2. Awafrican

    Awafrican Moderator Silver Member

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    As far as I know the disabling cold start just stops the runners in the intake manifold... Perhaps changes idle point a little. Could be way out in left field here. if you're misfiring because the engine is cold then you need to fix the cause of that misfire as this won't help
     
    Awafrican, via a mobile device, Feb 9, 2024
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  3. jsmith

    jsmith Silver Member

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    Changing cold start expected ECT (or something) was the way to lower cold start RPMs via tuning.
     
  4. jsilva

    jsilva Silver Member

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    I had read of several people saying they did that 5% throttle thing to avoid the CEL’s because of the cold start misfires. That’s all I’m wanting to do right now because I’m well past inspection and just need a quick fix.

    I do need to fix it and I’ve been trying to for months in the limited spare time I’ve had. I replaced the plugs, swapped ignition coils, replaced the injector on the misfiring cylinder, ran Seafoam top engine cleaner, fixed some small vacuum leaks, cleaned the EGR, etc. In the past this misfire was fixed by running Techron but that doesn’t seem to be doing the trick now.
     
  5. jsmith

    jsmith Silver Member

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    Are you running a fuel mix with ethanol? It could eliminate bad fuel as a culprit.
     
    jsmith, via an iPhone, Feb 9, 2024
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  6. jsilva

    jsilva Silver Member

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    Are you suggesting to run that or to fuel up with 100% gasoline?
     
  7. jsilva

    jsilva Silver Member

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    For anyone interested, here’s one of the threads I found:



    I just wasn’t sure what to expect the car to do. Mine revved up a bit and I wasn’t sure if by doing that the computer doesn’t try doing it on its own? And I wasn’t sure how long to leave the pedal slightly applied (really let it off immediately?). And I’m also not sure why that would stop cold start misfires (unless it also alters the AF ratio).
     
  8. jsmith

    jsmith Silver Member

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    I was suggesting the addition of ethanol, if you don’t already run some.

    edit: I believe a gallon or so to a full tank shouldn’t throw off fuel trims excessively.
     
    jsmith, via an iPhone, Feb 9, 2024
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  9. jsilva

    jsilva Silver Member

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    Interesting. I am in southeastern PA and try to use Shell V-Power but nowadays stations aren’t nearby and I usually end up using Sunoco Ultra 93. The pumps always say it contains ethanol. I can’t remember what the percentage is. I’ve only seen one station with 100% gasoline! A Wawa near Lancaster.

    What could adding ethanol do in terms of my issue?
     
  10. jsmith

    jsmith Silver Member

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    The usual gas has up to 10% ethanol. Most people tuning for power on stock fueling go up to e30 or so. You have to flow more volume of ethanol, as compared to gasoline, but it has a higher effective octane.

    Basically adding some to your full tank you raise octane and check if you just had a bad tank of gas that is causing misfires.
     
    jsmith, via a mobile device, Feb 10, 2024
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  11. jsilva

    jsilva Silver Member

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    Ok that makes sense, thanks. I had initially wondered if it was bad gas, or a dirty fuel tank. But it’s been months now and I’ve also used multiple fuel system cleaners. And I replaced the injector (it’s misfiring on just one cylinder). But trying some extra ethanol is worth a shot.

    I noticed yesterday that the spark plug on the misfiring cylinder is darker than the others (not wet). Not substantially but the others were the same and this one stood out because of that.
     
  12. RyGuyv

    RyGuyv Silver Member

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    This video shows how to do it.

     
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  13. Easter Bunny

    Easter Bunny Professional Engineer Motorhead Platinum Member

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    Check the wiring to the injector and spark plug
     
    Easter Bunny, via a mobile device, Feb 11, 2024
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  14. jsilva

    jsilva Silver Member

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    Interesting you say that… Years ago, before I rebuilt the engine, the injector completely failed for the same cylinder that’s misfiring now. I bought new injectors back then. Coincidence? Could faulty or weak wiring cause the injector to completely fail over time?
     
  15. SyntheticAtmosphere

    SyntheticAtmosphere You only get ONE ride, ONE ticket, ONE time! Silver Member

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    Yes, high or low resistance can wreak havok on the coil (in the injector). Voltage spikes also can affect its performance. Variances over time will cause issues with any electrical circuit, especially if it isnt engineered to handle them. That is why a good injector service shop will check the injector coil resistance, inductance and isolation.
    Could be an avenue to look into.
     
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  16. jsilva

    jsilva Silver Member

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    Thanks, I appreciate it. I’m not sure there are any specialized shops in my area but I will definitely do what I can. Are you able to advise? I usually need help knowing what exactly to test with electronics.

    And by the way, the video RyGuyv linked to was perfect. I’m able to avoid the cold start every time now. We’ll see if it keeps the misfire CEL away.
     
  17. SyntheticAtmosphere

    SyntheticAtmosphere You only get ONE ride, ONE ticket, ONE time! Silver Member

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    Consider getting your injectors cleaned if they are due and reinstalled with some good seals. Hard to say, "Years ago" is a pretty big spread. If the problem is resolved, then you need to decide if its worth digging into or just a coincidence.

    As with anything electrical start with the basics. Scrutinize all connectors, clean and apply grease if required Check pins/receivers and look for pulled or strained wires. Check wiring for condition such as dry outer sheath, bends, cracks then test for continuity and load test all circuits. This could be a very involved process. Could also be a problem with the PCM...so many variables, therefore 1 step at a time.

    Im just going off your idea its possibly related to the injector. If you have other possible causes to research I would consider those as well to avoid going down rabbit holes.
     
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  18. jsilva

    jsilva Silver Member

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    Thanks! I don’t think it’s the injector itself, but because of what Easter Bunny said I wonder if it’s the wiring, given that the injector on the same misfiring cylinder failed previously.

    I looked back at my notes and see that I replaced the injector wiring harness (used) back when I had replaced the failed injector. But then later on I switched back to the old wiring harness. I have no idea why, and I don’t know which one I used when I rebuilt the engine. I had tested both for continuity back then and they were both fine, but I did not load test. And if there is a wiring issue maybe it’s before that harness.

    I appreciate all of the suggestions!
     
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  19. Sleepy_Pat

    Sleepy_Pat Silver Member

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    If you've confirmed wiring and the injector isn't the issue, i'd move to the coil packs. Try stretching the spring that makes contact with the spark plug. Be careful as the springs may be on the fragile side. If you've verified the coil packs are good, i'd guess its time for a compression and leak down test for good measure.
     
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  20. jsilva

    jsilva Silver Member

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    I checked the fuel injector harness and it was fine. However, I had a temporary time where my car had no CELs and the readiness tests were all ok (I’ve also been having intermittent catalyst efficiency issues…), so I took the car in for emissions inspection and it passed.

    So I now have another year to work this out :)

    But when I took out the intake manifold it had a lot of oil in it. I’ve never seen even half that much. I replaced the PCV valve while I was at it but I wonder if the turbo is spitting oil.
     
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