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Thread: 1999 DeVille stalling, have codes

  1. #31
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 1999 DeVille stalling, have codes

    This post is for the 2000+, but yours should be similar except for the plenum duct (the rubber coupler) so you can ignore that part, but removing the manifold should be about the same.
    http://www.cadillacforums.com/forums...ent-steps.html


  2. #32
    COLOZZUS is offline Cadillac Owners Member
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    Re: 1999 DeVille stalling, have codes

    Hey, I replaced the blowback valve. Nothing's changed and I can still hear the hissing from the same section of the engine bay.

    Can anyone take a guess at why a cars rpm's would jump up and down between 500 and 1500 (approximately) and eventually stall out? This starts as soon as the car hits operating temperature (not a second sooner). I'll also mention that there is a heavy smell of gasoline during and after.

    Please help. I'm moving in a few weeks and need this car to be reliable. I've done most of what's been recommended. I've cleaned the tb, iac, replaced the intake manifold gasket, replaced the plugs and wires, cleaned the maf, replaced the Pcv valve, replaced the fuel filter, cleaned the coils and checked the fpr with no issues.

  3. #33
    basscatt's Avatar
    basscatt is offline Cadillac Owners 10000+ Posts
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    Re: 1999 DeVille stalling, have codes

    Quote Originally Posted by COLOZZUS View Post
    Hey, I replaced the blowback valve. Nothing's changed and I can still hear the hissing from the same section of the engine bay.

    Can anyone take a guess at why a cars rpm's would jump up and down between 500 and 1500 (approximately) and eventually stall out? This starts as soon as the car hits operating temperature (not a second sooner). I'll also mention that there is a heavy smell of gasoline during and after.

    Please help. I'm moving in a few weeks and need this car to be reliable. I've done most of what's been recommended. I've cleaned the tb, iac, replaced the intake manifold gasket, replaced the plugs and wires, cleaned the maf, replaced the Pcv valve, replaced the fuel filter, cleaned the coils and checked the fpr with no issues.
    -----------------------------------
    I can still hear the hissing from the same section of the engine bay.
    if you can hear the hissing -
    finding the vacuum leak should be easy -

    get a can of carb cleaner -

    put the little straw on the end -

    spray in the area of the hissing -

    when idle speed jumps - you found the leak -

    then simply pinpoint the leak and replace the leaking part -

  4. #34
    COLOZZUS is offline Cadillac Owners Member
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    Re: 1999 DeVille stalling, have codes

    Quote Originally Posted by basscatt View Post
    -----------------------------------
    I can still hear the hissing from the same section of the engine bay.
    if you can hear the hissing -
    finding the vacuum leak should be easy -

    get a can of carb cleaner -

    put the little straw on the end -

    spray in the area of the hissing -

    when idle speed jumps - you found the leak -

    then simply pinpoint the leak and replace the leaking part -
    Do you think that a vacuum could cause the issue described above (rpm jumping up and down at operating temperature)?

  5. #35
    basscatt's Avatar
    basscatt is offline Cadillac Owners 10000+ Posts
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    Re: 1999 DeVille stalling, have codes

    Quote Originally Posted by COLOZZUS View Post
    Do you think that a vacuum could cause the issue described above (rpm jumping up and down at operating temperature)?
    ------------------
    YES -
    the engine probably runs relatively smooth at start-up - when cold -
    as it warms - it runs rough - or at least "rougher" -

    that is because the air/fuel mixture is adjusted "richer" when the engine is cold -

    that "richer" mixture is compensating for the vacuum leak -

    as the engine approaches normal operating temps -
    the air/fuel mixture "leans-out" to the "normal" mixture -

    but now with the vacuum leak - the engine is running too lean -
    and is trying to compensate for the "un-metered air" being sucked in -

  6. #36
    COLOZZUS is offline Cadillac Owners Member
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    Re: 1999 DeVille stalling, have codes

    Quote Originally Posted by basscatt View Post
    ------------------
    YES -
    the engine probably runs relatively smooth at start-up - when cold -
    as it warms - it runs rough - or at least "rougher" -

    that is because the air/fuel mixture is adjusted "richer" when the engine is cold -

    that "richer" mixture is compensating for the vacuum leak -

    as the engine approaches normal operating temps -
    the air/fuel mixture "leans-out" to the "normal" mixture -

    but now with the vacuum leak - the engine is running too lean -
    and is trying to compensate for the "un-metered air" being sucked in -
    Thanks basscat, I appreciate you taking the time to explain. I completely understand. I'll spray the area where the hissing is coming from.

  7. #37
    Ranger's Avatar
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    Re: 1999 DeVille stalling, have codes

    We told him to check for a vacuum leak back in post #8 & 15.

  8. #38
    COLOZZUS is offline Cadillac Owners Member
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    Re: 1999 DeVille stalling, have codes

    Quote Originally Posted by Ranger View Post
    We told him to check for a vacuum leak back in post #8 & 15.

    Yes, you did mention that. Many other things were mentioned as well and I went out and replaced, repaired or cleaned those things. I just wish some one early on, would have explained the connection between the issue at operating temperature and the vacuum leak. I honestly never gave the "vacuum leak" much weight because I figured if there was a leak, the engine would act the same from start to stall. No worries. Though many of the things recommended may not have been the main problem, they could have contributed to the current issue or given me trouble down the line. I always appreciate any help I can get.

    I sprayed down every single hose I could find, among many other parts and lines. I went through about 3 cans of cleaner trying to find a vacuum leak and found nothing. The hissing now only seems to occur when I push on the gas pedal and just about a second after or when the car starts to jump up and down in rpm's. I had a friend lighty hold the gas pedal down, while I listened with the stethoscope to try and pinpoint where the hissing is coming from. All I could tell was that the hissing got louder as I got closer to the bottom of the blowback valve opening. I almost want to say near the manifold gasket. After spraying everything down I figured I would get some codes for spraying something that I shouldn't have, so I checked the codes. Only codes I got were

    P0147-HO2S Heater Performance Bank 1 Sensor 3
    C1737-Exhaust Solenoid Valve Short to Battery

    I humbly say thanks to all for your help

  9. #39
    Ranger's Avatar
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    Re: 1999 DeVille stalling, have codes

    All I could tell was that the hissing got louder as I got closer to the bottom of the blowback valve opening.
    To rule out the over pressure relief valve, push in on it to seal it tighter with a long screwdriver, dowel rod or such. Also check the vacuum line next to it. See the picture in post #19.

  10. #40
    COLOZZUS is offline Cadillac Owners Member
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    Re: 1999 DeVille stalling, have codes

    Quote Originally Posted by Ranger View Post
    To rule out the over pressure relief valve, push in on it to seal it tighter with a long screwdriver, dowel rod or such. Also check the vacuum line next to it. See the picture in post #19.
    Thanks for the advice. I did what you said and pushed down the relief valve. Unfortunately it didn't change the hissing. I also removed the vacuum line attached to the relief valve and it started a new hiss of its own. Once I hooked the vacuum line back up the new hissing went away but the other is still there. I'm going to look to see if there are any vacuum lines under or near the power steering resovior besides the one that hooks up to the relief valve. Thanks

  11. #41
    Ranger's Avatar
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    Re: 1999 DeVille stalling, have codes

    A stethoscope will make that hiss sound like a hurricane and thus much easier to locate.

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