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Thread: DIY Air Assist Valve Delete for Upgraded Injectors

  1. #1
    Senior Member Spoolin_VTEC's Avatar
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    DIY Air Assist Valve Delete for Upgraded Injectors

    For those with upgraded injectors, this may or may not be an issue you've experienced. I have RC 550cc injectors. Vit has RC 370cc injectors. We've both noticed an issue with cold starts, but not in the normal sense of it being hard to start the car. It's been the type of thing where the car will rev hang excessively until the coolant has warmed up to about 120 degrees. Occasionally the idle will bounce a bit and rev up past 2000 rpm as well.

    Vit and I have been working together for the last few days trying to troubleshoot and eliminate this process through a variety of tuning angles to no avail. Today I finally emailed Doug at Hondata about it.

    Here's the advice he gave that ended up being the solution:

    "On the intake manifold near cylinder 4 you will find a cold start thermostat valve. It bleeds air from the intake to behind the injectors to help atomize the fuel until the coolant temperature rises. I am not sure if it does anything with the RC injectors, but try blocking these hoses off."

    Vit decided to give this a go first and had promising initial results. I did the same and just got back from testing it after the car had cooled down. It appears to have totally and completely fixed the problem. :dancing:

    Here's why:

    On the OEM injectors there are little holes in the nose of the injector that allow the air from this Air Assist Valve to enter the fuel stream on cold idle and help atomize the fuel better to reduce emissions while the engine is warming up.

    See the picture below and note the 2 o-rings (orange and black) and the tiny hole for air to come into the fuel stream through.

    The OEM injector uses the 2 o-ring design to force the air from the Air Assist Valve to pass through the tiny hole in the injector tip. This limits the amount of air that the engine can naturally pump through this passage to a very tiny amount. So little that it won't affect the way the car runs normally.

    The RC injectors have a short tip that doesn't have the second smaller (orange) o-ring. There's no small hole for the air to flow through either.

    The lack of these two things has the effect of allowing the engine to pump much larger amounts of air through this passageway than was originally intended. This heavily affects every aspect of cold start idle and driving since this air has not been measured by the engine in any way. The ECU notices that it's lean so it dumps fuel, then it notices that it's rich and goes back and forth.

    The Air Assist Valve closes around 120*F so after the coolant warms up to that point, the issue goes away.

    How do you do this on your car?

    Super simple, just block off the hose that allows air to flow into the system. As a test, I just cut the hose, stuck a couple bolts in it and taped/zip tied it to make sure it wouldn't leak.

    For the long term fix, I bought some 1/2" and 3/8" vacuum plugs and a 3/8" NPT plug.

    The hole you need to plug on the intake manifold. Make sure the engine is cold before removing this. If it's cold, no coolant will come out of this when you remove it.

    Here's the valve removed.

    Just slip one of the 1/2" vacuum plugs on the intake tube. Since this tube only sees vacuum, there's no need to clamp this one as long as it's snug.

    I used a 3/8" vacuum plug on the IM side, I put a clamp on it as well. I'm paranoid since I have positive pressure coming through the IM. N/A guys won't need this since they don't have boost (I probably don't need it either, but better safe than sorry).

    Here's the 3/8" NPT plug. I bought it at Autozone for $1.49

    For anything like this, it's best to apply some sort of thread sealant to keep the plug from leaking. I used this high temperature permatex thread sealant. Be sure to read the instructions on the package and apply it properly.

    NPT plug installed. Snug it down nice and tight.

    Does this apply to you?

    If you're using an injector with a short tip that doesn't have a 2 o-ring setup, yes probably. But if it isn't broke, don't fix it. Only make this modification if you notice the symptoms described above.

    Quoted from Jay Mucter

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  4. #2
    Super Moderator
    Spaz's Avatar
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    Nice write up. I used an inverted NPT plug for a cleaner flush look
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  5. #3 Founder

    BoostedK20's Avatar
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    Fixed pictures. Great write up/find!

  6. #4
    I <3 Purpul Shocker
    Si Speed 317's Avatar
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    Doing this ASAP.

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