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Thread: Finding cause of loss of rest pressure

  1. #11
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by Ron View Post
    The post 1978 and adjustable have one that looks like this (but the small o-ring you mentioned is missing):
    Attachment 65555
    To get to the push up o-ring, push the keeper ring back (see arrow) to expose a tiny snap ring. Remove it and the rest should be obvious...
    Yes. That is what I have. Never took the snap ring off. That photo is also missing the shim.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  2. #12
    Senior Member Bitsyncmaster's Avatar
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    Simple adapter to test pressure loss or pump max pressure after the accumulator. I would not recommend testing max pump pressure here though because your subjecting the accumulator to that max pressure. It should hold it anyway.

    You may be able to build one if you can find an adapter that has 12 mm 1.5 thread going to a hose nipple or pipe thread.
    Attached Images
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #13
    Senior Member Bitsyncmaster's Avatar
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    Well it pegged my gauge with just a short run of the pump. Was reading probably about 130 PSI. What I can do is power the pump with my bench supply at a lower voltage. But anyway I purged the air and it was 73 PSI at 5:38 pm.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  4. #14
    Senior Member Bitsyncmaster's Avatar
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    Finding cause of loss of rest pressure

    Well I should have started a new thread on "Finding cause of loss of rest pressure" so owners can find it.

    After 12 hours my car is still holding 47 PSI with the gauge attached to the fuel line from the output of the fuel accumulator. So I've verified this is a good test that would eliminate the check valve, accumulator and connections on those. Now I will do this test on that local owners car next time he comes down my way. I wonder if the fuel gauge test sets already have an adapter to do this test. I did find the first hour of this test my pressure dropped about 10 PSI and the amount of drop has drastically been reduced following. So I'm wondering what is the cause of this small pressure drop. I'm guessing it may be the check valve is not perfect. But is also could be my test setup which has my pressure gauge on a T and a shutoff valve also on that T along with the hollow bolt connections. Last time I checked normal rest pressure on my car it held about 3 hours until it dropped to zero PSI.

    Now the primary pressure regulator has that one small O-ring that makes the seal on the side with rest pressure. It is my understanding on the other side of that "piston" that chamber is connected to the return line which is open to the tank (0 PSI). Is this assumption correct? If so any other o-rings and the copper washer really do nothing for rest pressure.

    So that would leave the injectors, the cold start valve, the warmup regulator and all the lines as to rest pressure loss.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  5. #15
    Administrator Ron's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    ...

    Now the primary pressure regulator has that one small O-ring that makes the seal on the side with rest pressure. It is my understanding on the other side of that "piston" that chamber is connected to the return line which is open to the tank (0 PSI). Is this assumption correct? If so any other o-rings and the copper washer really do nothing for rest pressure.
    PUSH-CPR.jpg

  6. #16
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by Ron View Post
    Thanks for moving the thread Ron.

    So it does look like the top side of the piston is always open to the tank return line.

    My pressure after 36 hours is still at 43 PSI. It was at 44 PSI at 24 hours so it looks like it will not loose anymore for a longer time. I have the Tahoe fuel pump and the external check valve in my car. I'm guessing the check valve (valves) may be what looses pressure above that 44 PSI. But this test does show me my limit for holding rest pressure (three hours in my case) is caused by the system from the fuel distributor, injectors, cold start or lines.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  7. #17
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  8. #18
    Senior Member Bitsyncmaster's Avatar
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    I'm still at 43 PSI and holding many days after starting this test on my car. I thought I could also test the volume of the accumulator with this setup but can't think of any reason you would need to know that. Just release the pressure into a jar and measure the gas released.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  9. #19
    Senior Member Bitsyncmaster's Avatar
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    Here is a interesting tidbit of info. Well after about a week with it holding around 44 PSI, I released the pressure and it leaked out the gas pretty slowly (about 30 seconds). I could also hear the accumulator clunking during that release which it normal as rest pressure drops.

    So the back flow from the accumulator has a limited volume/second. I'm guessing there is a small orifice feeding the accumulator bladder. What that means is if the bladder spits your car should still run fine and the small amount from the split would feed back to the tank.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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