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Diagnosing hard warm start

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    #1

    Diagnosing hard warm start

    I've got a small issue, I'd like to sort out. When cold (sitting for hours) the car starts reliably on the first try (takes a couple seconds, but consistent). If the car is only shut off for a little while (<30 minutes), it also starts up on the first try (generally quickly). However, if the car has been shut off for a medium duration (30+ minutes), it will take 2 starts (sometimes one really long one). The second start is usually really fast and it starts right up. The problem seems worse with the weather is hot. The car runs great once started.

    Based on my research, it could be 3 things:

    1. leaky injectors (they probably have 165k on them)

    2. coolant temp sensor (cheap/easy)

    3. crank position sensor (checked resistance, checks out)

    How would I diagnose this issue without just replacing? Are there any other items that I should look at? I've already replaced the fuel pump relay, and the fuel pump was recently replaced also. I have a feeling it is either the injectors or temp sensor. Biggest question is around how to check for a leaky injector.

    Thanks in advance!
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    #2
    Fuel pressure Regulator leaking off when warm
    Originally posted by Fusion
    If a car is the epitome of freedom, than an electric car is house arrest with your wife titty fucking your next door neighbor.
    The American Republic will endure until the day Congress discovers that it can bribe the public with the public's money. -Alexis de Tocqueville


    The Desire to Save Humanity is Always a False Front for the Urge to Rule it- H. L. Mencken

    Necessity is the plea for every infringement of human freedom. It is the argument of tyrants.
    William Pitt-

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      #3
      Do a smoke test with a warm engine. Things like to expand with higher temp.

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        #4
        Put a fuel pressure gauge on it and watch.

        If an injector is leaking, pressure will drop slowly as the fuel gets into the engine.

        If pressure holds, you've ruled out all pressure- holding issues- all the injectors,
        the valve in the pump, the regulator, leaks, aliens stealing the fuel out of your pressure test port...

        hth

        t
        now, sometimes I just mess with people. It's more entertaining that way. george graves

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          #5
          To test the pressure, install gauge, jump relay and observe after shutting off fuel pump?


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            #6
            Looked up some how to's on YouTube. Ordered a pressure tester and some fuel line (return line was cracked at FPR). Will just replace supply and return line while at it.


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              #7
              If the rail was loosing pressure due to a bad FPR or bad pump check valve the problem would be worse after the car sits overnight. Leaking injectors can cause exactly the symptoms you see. Pull the injectors and have them professionally cleaned, rebuilt, and flow tested. I like RC Engineering.
              The car makes it possible, but the driver makes it happen.
              Jim Levie, Huntsville, AL

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                #8
                Originally posted by jlevie View Post
                If the rail was loosing pressure due to a bad FPR or bad pump check valve the problem would be worse after the car sits overnight. Leaking injectors can cause exactly the symptoms you see. Pull the injectors and have them professionally cleaned, rebuilt, and flow tested. I like RC Engineering.
                Yeah, this is what I figure as well. I'm going to change the coolant sensors anyway, since they are cheap, and my gauge jumps around a bit, but I'm pretty sure it's a leaky injector based on the symptoms.

                Anyone bought refurbed injectors from catuned.com?

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                  #9
                  Ok. I hooked up a pressure tester this AM. Pressure is good when running 40PSI. FPR seems to be doing its job when blipping throttle. When the engine shuts off, pressure goes to 0 fast. I'm guessing this is the sign of a leaky injector. How would I rule out FPR? Should I just replace both?

                  VimeUhOh
                  https://vimeo.com/184121058
                  Sorry, we couldn’t find that page



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                    #10
                    Take the return line off when car is off and see if fuel comes out the regulator is easiest way to see if its leaking. Also if you could pinch the feed line off with vise grips that would tell you if its leaking back to tank from the pump.

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                      #11
                      Thanks. I'm a little worried about damaging the line by pinching it. I'll give it a shot when I replace the lines (already planned).


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                        #12
                        Alright before you buy new injectors/ fpr/ anything get a good tool that will grip the fuel lines without damaging them, but restricting flow. Do the same test but clamp the return hose off the rail that goes back to the tank. If the pressure stays, your injectors are NOT leaking. If the pressure drops its probably injectors/ fpr. Use this method to clamp off different parts of the system until you figure out which piece is causing the pressure loss.

                        Check for leaks and I would read a few of the plugs after you drove it and it died. http://www.onallcylinders.com/2012/1...r-spark-plugs/

                        It seems like it probably is injectors leaking/ making your car run too rich. But get solid diag before you throw parts at it
                        BMW tech
                        Umass Amherst
                        05 wrx sti

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                          #13
                          This has all been very instructive. I feel like leaking injectors would also explain the off throttle "burbling" the car makes. It sounds cool, but it's probably excess unburnt fuel. I've never had an m20 or e30, so don't know what's normal. Also I only get 20mpg which is less than I expect.


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                            #14
                            any updates? mine also does this when warm. it'll bogg out every time i crank it up. usually starts up roughly on 3rd/4th crank

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                              #15
                              Bumping for a follow-up as well.
                              1985 325e Sedan, 1986 325e Sedan, 2006 BMW X5, 2012 M3 Sedan, 2013 135is, 2017 M3 Sedan ZCP Competition

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