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Thread: No power, won't rev under load. Low fuel pressure.

  1. #1
    Member Roadster's Avatar
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    No power, won't rev under load. Low fuel pressure.

    My car ran great until she sat for a while. Starts up from cold immediately but over about 2000 RPM or so under load it is undriveable. Car hesitates and acts like it may be starved of fuel.

    The car will rev in neutral with some hesitation at first. I checked the pressure, normal running pressure is 20 at most, I know this is low. When I close off the valve to the CPR I get 70 PSI in the line from the top of the fuel distributor which should be fine. I've watched other people check pressure and close off the valve and the car stays running, when I do it the engine dies. It fires up again immediately.

    If I'm getting 70 psi at any point doesn't that suggest the pump should be good? It's only a few years old. I'm thinking the CPR/WUR is bad which is unfortunate as I had it rebuilt a couple years ago. I know the heater element in it is broken but it hasn't been much of an issue.

    Anything else you can suggest to check the CPR would be helpful. I'm hesitant to throw one at it with how expensive they are. Thank you!

  2. #2
    Senior Member Bitsyncmaster's Avatar
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    That sounds like your fuel filter is plugged.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #3
    Administrator Ron's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    That sounds like your fuel filter is plugged.
    I'm thinking you missed him saying it's getting 70 psi out of the FD??

    =====

    A restriction at the CPR will raise the pressure too high. So, if it's getting 70 psi from the FD and it never raises the control pressure above 20 psi, it's bad.

  4. #4
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by Ron View Post
    I'm thinking you missed him saying it's getting 70 psi out of the FD??

    =====

    A restriction at the CPR will raise the pressure too high. So, if it's getting 70 psi from the FD and it never raises the control pressure above 20 psi, it's bad.
    My thought is low flow rate because of almost plugged filter when engine is under load.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  5. #5
    Administrator Ron's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    My thought is low flow rate because of almost plugged filter when engine is under load.
    I'm with ya.
    With the injectors not opening until ~55 psi and it having 20 psi left over (through the decoupling restrictor) at 2000 RPM, it would have to be just right tho....Good thinking!
    ~$20.00 would tell which.

  6. #6
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    Do you hear the frequency valve buzzing? If not, that would make the car run very lean.
    David Teitelbaum

  7. #7
    Member Roadster's Avatar
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    Quote Originally Posted by David T View Post
    Do you hear the frequency valve buzzing? If not, that would make the car run very lean.
    I do not recall specifically hearing the frequency valve buzzing. The exhaust is so darn loud in the garage I may have drowned it out. I'll try to isolate the sound of that more tonight.

  8. #8
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    Quote Originally Posted by Roadster View Post
    The car will rev in neutral with some hesitation at first. !
    When you say this, are you saying after a bit you can't even rev it in neutral? If that's the case, I would check the pressure after it won't rev in neutral. If the pressure is going down, Either a clogging filter or maybe the fuel pump is losing power. I had an issue where I didn't have 12V at the pump.

  9. #9
    Member Roadster's Avatar
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    Quote Originally Posted by Helirich View Post
    When you say this, are you saying after a bit you can't even rev it in neutral? If that's the case, I would check the pressure after it won't rev in neutral. If the pressure is going down, Either a clogging filter or maybe the fuel pump is losing power. I had an issue where I didn't have 12V at the pump.
    I can still rev it in neutral, there just seems to be a bit of hesitation at first. I just tried it again, fired up immediately from a cold start and settled at 24psi constant running. Shutting the engine off the pressure goes up to 39psi and holds. Frequency valve is still buzzing away while it runs.

    I shut it off and tried again a few minutes later. Pressure was now down to 15 psi constant running. Shutting the valve on the tester to the CPR spiked the pressure up to 70 but stalls the engine quickly.

    Pump and filter are not that old, but not out of the question. CPR has failed before which is why I suspect it again. Also after this is warmed up and experiencing the issue the car seems to be running crazy rich, hurts your eyes just to be back there checking it over.

  10. #10
    Administrator Ron's Avatar
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    Quote Originally Posted by Roadster View Post
    Shutting the engine off the pressure goes up to 39psi and holds.
    Then, at that point, the CPR had to be holding at least 39 psi. ...Bitsy's idea about the filter is looking very promising.

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