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Cavalier injectors

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  • Cavalier injectors

    So I have a couple of bad injectors on my 2004 Chevy Cavalier. I found that you can buy Keihin blue injectors online, which inject the correct amount of CNG (52cc) but do not completely fit physically. It fits, but does not seal against the hole in the cylinder. I was wondering if it would be possible to put an O-ring on the narrow brass part of the new injector (see photo) to make it seal against the hole the injector inserts into. I suspect it would take multiple O-rings to make sure that they cannot move. Does anyone see a reason why this would be a bad idea? Is there a better way to do this?
    Left: Original CNG injector Right: New one

  • #2
    Edit: you probably don't want to do this because apparently the old injectors flow more fuel than the new ones. I'll try to find out if this can be dealt with by getting a different sized injector.

    I got this working so I thought I'd post what I did for the benefit of anyone else who can't find used injectors. I'm no expert and don't know for sure if you can ruin your car by doing this so apply your own judgement. Maybe someone who knows more than I do can post some more information. Basically, there are two problems to solve: the new injectors are too wide above the brass tube, and the brass tube is too narrow to use a standard size O-ring for this.

    I used a 1/4" copper coupling and two sizes of O-rings to make two seals using O-rings that are standard sizes. First, I put a 3mmx5mm O-ring on the brass tube on the injector to prevent contact between the coupling and the injector - I imagine that could damage the injector and possibly cause galvanic corrosion of the copper. Then, I put three 2mmx5.5mm O-rings on the brass tube. I cut the copper coupling to fit and put it over those O-rings. You should cut it to about 5/8" long.

    I drilled out the plastic housing the injector passes through using a 3/4" countersink. I put a wadded up paper towel inside the hole to keep plastic filings out and inserted the injector and put on the CNG rail periodically to make sure I drilled out the plastic only as far as needed.

    Then, I put 4 size 013 O-rings inside the hole and inserted the injector and reassembled everything. Actually it's probably easier to put the copper tube in the hole and then push the O-rings onto it; that's a tight fit.

    I got the injectors on Ebay. also has them but you have to call to order them. Search "Keihin blue cng injector". Blue turns out to mean 52cc although I don't know if that's cubic centimeters at the pressure in the regulator or standard cc.
    I used viton O-rings because I know gasoline won't dissolve them. I'm not aware of any other material that will work (thank you hypermilinggx for pointing out that silicone is a bad idea even if there are types that aren't ruined by gasoline). There are routes you might like to making O-rings from gasket maker (sillicone, don't do it) or by splicing O-rings of the right thickness and gluing them (sounds really unlikely to be leaktight plus the adhesive might get dissolved). I got the O-rings from
    The 1/4" copper coupling actually has an inside diameter of more than 1/4". Don't ask me why the imperial system of units is like that - as a side note nominal imperial O-ring sizes are not the actual sizes. This is the coupling I got:
    Last edited by dkane; 09-29-2017, 11:40 AM.


    • #3
      Whatever works, EXCEPT silicone, which will ruin the oxygen sensor.


      • #4
        So I somewhat got this working. I ended up replacing all the injectors. Turns out the flow rate on the new ones is about half what it was on the old ones (not sure why Keihin changed that). Now it runs fine on CNG but the OBD2 oxygen sensor and oxygen sensor heater tests will not run when doing the drive cycle (or any other time). They do run on gasoline. The idle speed drops a few seconds after starting the car cold then it's fine. Fuel trims are near zero, and the downstream O2 sensor reads near 0V most of the time. Any thoughts on what to do about that?


        • #5
          Actually the monitors ran on CNG after they ran on gasoline. I hadn't realized it was necessary to make them run on gasoline first.