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P030x errors- possible fuel pressure regulator

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Bigger, May 11, 2017.

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  1. Bigger

    Bigger Junior Member

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    (This thread revives my older thread, "Very rough idle, several DTCs, odd smelling exhaust," wherein I describe my misadventures trying to track down the problem. Now I think we figured it out, but before I lay out a heap of money for a new fuel tank, I crave some reassurance)

    My friend, a much more experienced mechanic than I am, came to help me figure out why our Prius was misbehaving.

    2005 Prius
    225k miles
    well maintained
    Smart key
    Has always been reliable but has started roughly a few times before.
    Spontaneously started misfiring badly a few weeks ago and barely limped home, crying out P0A0F P0300 P0303 P0304

    Please read the other thread (Very rough idle, several DTCs, odd smelling exhaust | Page 2 | PriusChat) for the things we've already tried. Fruitlessly. One mistake in the other thread is the age of the plugs- I replaced the plugs in our older Prius, not this one. These plugs are at least four years old (that is when we bought the car).

    To reiterate the symptoms, we got very rough idle, and exhaust that smells like incompletely burned gas. We always get P0304, usually get P0303, occasionally get P0302, never get P0301. Very rich mixture.

    After a two-day subscription to TIS and much head scratching, we replaced the plugs (which were carbon fouled, with crusty carbon deposits), with no improvement. Switching COPs did not move the problem. My friend suspected fouled injectors, so he unplugged the fuel pump and we ran the car to depressurize the fuel rail.

    The car started, running rough for two seconds- then smoothed right out and ran properly! For six more seconds before the computer freaked out that it had low fuel pressure. So we used jumper wires to connect the fuel pump wiring block back up but selectively turned off the fuel pump. Whenever the fuel pump was disconnected, after a few seconds, the engine smooths right out and runs as it should.

    Our suspicion is that the fuel pump regulator is out of whack, allowing much to high pressure fuel. This puts too much fuel through the injectors (hello, super rich mixture smell) any time the fuel pump is running. When we turn off the fuel pump, the pressure still in the system remains too high for the first two seconds, then continues to descend for six seconds of smooth sailing, then the engine senses that the mix is going too lean and shuts the engine down to avoid damage.

    So, I'm going to be looking for a fuel tank. Since this is rather above my 'spend without worry' number, I'm hoping that some people can chime in and either confirm or correct my logic.
     
    #1 Bigger, May 11, 2017
  2. dolj

    dolj Senior Member

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    Can you not connect a pressure gauge to the fuel rail and confirm whether the pump is at spec pressure?

    According well respected member Patrick Wong, he says (in this post in the thread P3193 code) it should be > 43 PSI, but doesn't say if there is a maximum pressure. Maybe TIS does.

    I think you are on the right track, but personally I'd want some kind of test to confirm my diagnosis before ripping into replacing the fuel tank.
     
    #2 dolj, May 11, 2017
    Last edited: May 11, 2017
    Bigger and Patrick Wong like this.
  3. Bigger

    Bigger Junior Member

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    Is there a place where we can easily access the fuel rail? It looks to be quite well buried
     
    #3 Bigger, May 11, 2017
  4. dolj

    dolj Senior Member

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    I haven't had to do it myself and I don't know if Patrick has, but maybe have a look at work up for codes P0190 - P0194 in TechInfo. Possibly it has the procedure.
     
    #4 dolj, May 11, 2017
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

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    The place to access the fuel line is where the fuel delivery pipe (which connects to the injectors) receives fuel from the fuel tube in the engine compartment. You might have to remove the cowl tray that houses the windshield wiper motor, for access, since this is at the back of the engine. Then you have to fabricate a T-fitting with a hose leading to a fuel tube connector and the other hoses connecting to the fuel pressure gauge and the fuel delivery pipe. The concept is to be able to measure fuel pump pressure with the injectors downstream. The spec is 44 to 50 psi. After the engine is stopped, the fuel pressure should be at least 21 psi after 5 minutes.

    If you find the fuel line pressure is correct, you can test the injectors. You can test them by removing the injectors and fabricating a test setup so that one injector is fed by the fuel line and is spraying into a glass container. The injector wiring harness terminals are connected to a 12V source. The injector is supposed to produce 2.1 to 2.8 cubic inches after 15 seconds of operation. Also, resistance across the injector wiring harness terminals is supposed to be 13.45 to 14.15 ohms at 68 degrees F.

    I would ask you to consider whether the engine is really running, during the six seconds after you've disconnected the fuel pump power. An alternative might be that MG1 is just spinning the engine. To test whether the engine is running, depress the accelerator pedal and see if the engine speeds up. If it does not, then the engine is not actually running.

    When was the last time the iridium spark plugs were replaced, prior to your recent service?

    I think you should test cylinder compression to see how worn out the engine is. Use Mini VCI to spin the engine under the cylinder compression test. If you don't, MG1 will spin the engine at 1,200 RPM which is not a good test.
     
    #5 Patrick Wong, May 12, 2017
  6. Bigger

    Bigger Junior Member

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    We will try this next week. Thank you for the clear direction.
    The engine does respond to throttle- I think. IIRC touching the throttle brings the RPMs up to around 1500 and smooths out the stumbling, but I do not recall if we did this during these steps. We did keep the engine running for over 15 seconds by unplugging and re=plugging-in the fuel pump.
    At least four years. They were carbon fouled (probably from the recent rich running).
    We will test this next week as well.

    Thank you.
     
    #6 Bigger, May 12, 2017
  7. Kstoner

    Kstoner New Member

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    Any luck fixing this??? Having the same issues my man.
     
    #7 Kstoner, Jul 30, 2019
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  8. BlueDragon

    BlueDragon New Member

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    Does anyone know the outcome of this thread? My 2010 has exactly the same symptoms.
     
    #8 BlueDragon, Oct 7, 2019
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