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Thread: hard start hot

  1. #1

    Default hard start hot

    1989 corvette hard to start warm. Fires immediately cold. Is this an O2 sensor problem. Exhaust is very clean , almost not soot. If so what is best O2 to buy?

  2. #2
    Join Date
    Dec 2011
    Location
    New Haven, Ct
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    HI there,

    NO, the oxygen sensor will NOT account for a hard start. I would start by checking your fuel injector resistance HOT. 16.5 on average +/- 1.5 ohm

    Allthebest, Paul
    GM World Class Certified Service Technician.
    Like us on Facebook: www.facebook.com/corvettemechanic
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  3. #3

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    Quote Originally Posted by c4c5specialist View Post
    HI there,

    NO, the oxygen sensor will NOT account for a hard start. I would start by checking your fuel injector resistance HOT. 16.5 on average +/- 1.5 ohm

    Allthebest, Paul
    Thank you Will do

  4. #4

    Default

    Sorry to take so long was a little under the weather. Is # 4 creating my problem?

    # 1--17.0 #2-- 17.1
    # 3--17.2 #4--15.3
    #5--17.1 #6--17.2
    #7--17.2 #8-- 17.4

    Thank You
    Ken

  5. #5
    Join Date
    Dec 2011
    Location
    New Haven, Ct
    Posts
    956

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    Hi there,

    It could be, however, I would also check standing fuel pressure after key up, 41-47 but I like to see 45 psi. After you start it, pressure should drop about 10 psi.

    Let us know, Paul
    GM World Class Certified Service Technician.
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  6. #6

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    Will try this afternoon when I get home. Thanks Ken

  7. #7

    Default

    COLD
    Key on no reading ( may be Gauge)
    41 when pump runs
    39 as soon as pump shuts off
    43 while cranking 1 2 seconds to start
    35 running
    34 light throttle
    Off
    15 minutes pressure 28
    Key on 40 PSI
    Start 35 PSI crack throttle open jumps to 42PSI then immediate back to 35PSI

    HOT 200*
    Key on 41PSI
    Running 35 PSI
    Turn off slow climb to 42 PSI
    After 7 minutes still 41 PSI
    Key on 40 PSI started immediately
    Drop back to 35 PSI running
    15 minutes still 40 PSI, 23 minutes still 32 PSI 43 minutes 6PSI
    Key on 42 PSI moderate hard start
    Running 35 PSI
    Increase RPM drops to 32PSI
    Shut off went to 40 PSI
    Last edited by ken mohr; 08-28-2020 at 02:15 PM.

  8. #8

    Default

    Now detecting miss at low RPMS and idle. Starting hot detect raw gas odor.

  9. #9
    Join Date
    Dec 2011
    Location
    New Haven, Ct
    Posts
    956

    Default

    HI Ken,

    Take the vacuum source off the fuel pressure regulator, plug it. Now then, try to start your vehicle or run the vehicle and see if any gas weeps out of the vacuum port at the top of the fuel pressure regulator. There should be none. The pressure readings were ok, but not great and if the regulator leaks fuel into the intake, it smothers the engine.

    Allthebest, Paul
    GM World Class Certified Service Technician.
    Like us on Facebook: www.facebook.com/corvettemechanic
    Twitter: www.twitter.com/GMvettemechanic

  10. #10

    Default

    Quote Originally Posted by c4c5specialist View Post
    HI Ken,

    Take the vacuum source off the fuel pressure regulator, plug it. Now then, try to start your vehicle or run the vehicle and see if any gas weeps out of the vacuum port at the top of the fuel pressure regulator. There should be none. The pressure readings were ok, but not great and if the regulator leaks fuel into the intake, it smothers the engine.

    Allthebest, Paul
    Ok will do. Thanks

  11. #11

    Default

    No gas weep. Starting to think ignition. Had 2 strong back fires. Runs smooth cold then starts to slightly misfire as it warms.

  12. #12

    Default

    Changed coil, rotor cap, rotor, and ICM. Runs great but still slow to start smell raw gas and some backfire.

  13. #13
    Join Date
    Dec 2011
    Location
    New Haven, Ct
    Posts
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    This is strange, because with the steady fuel pressure and its not dropping, I wouldnt think leaking injector.

    Did you do the fuel pressure test HOT ????

    Otherwise, my next move would be to investigate the injectors individually.

    Allthebest, Paul
    GM World Class Certified Service Technician.
    Like us on Facebook: www.facebook.com/corvettemechanic
    Twitter: www.twitter.com/GMvettemechanic

  14. #14

    Default

    Quote Originally Posted by c4c5specialist View Post
    This is strange, because with the steady fuel pressure and its not dropping, I wouldnt think leaking injector.

    Did you do the fuel pressure test HOT ????

    Otherwise, my next move would be to investigate the injectors individually.

    Allthebest, Paul
    I believe so. I will do it again

  15. #15

    Default

    It was the fuel regulator. All is well now. Fires on 1st compression stroke hot or cold. Thanks

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