96 Deville now throwing a P0171 and P0174 Codes.
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, 96 Deville now throwing a P0171 and P0174 Codes. in Past Cadillac Vehicle Discussion; Hello Forum Friends. I posted before about my 1996 Deville Northstar 4.6. Replaced the Fuel Pressure Regulator and now its ...
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    ralphieboy57 is offline Cadillac Owners Member
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    96 Deville now throwing a P0171 and P0174 Codes.

    Hello Forum Friends. I posted before about my 1996 Deville Northstar 4.6. Replaced the Fuel Pressure Regulator and now its throwing a P0171 (Fuel Trim System Lean,Bank 1) and a P0174 (Fuel Trim System Lean,Bank 1) codes. I looked through the Forum and found that its probably a cracked Throttle Body Plenum thus causing a vacuum leak. But I just read that the 1996 Northstar 4.6 motor dosn't apply to this. Ive checked the vacuum hoses and intake manifold but no leaks that I can detect. Were would be the best place to start troubleshooting? Is there a step process I should follow?

    I love my Deville but need it to pass smog so I can get my registration straightened out. So far Ive replaced the plugs and plug wires, air cleaner, fuel pressure regulator, and cleaned the throttle body out, oh and new front motor mounts. Any help would be greatly appreciated.

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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 96 Deville now throwing a P0171 and P0174 Codes.

    WOW! I could read that without my cheaters.

    Have you checked the manifold over pressurization valve in the tunnel behind the P/S pump? If it is not seated or the seal is damaged it will cause a vacuum leak.




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    ralphieboy57 is offline Cadillac Owners Member
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    Re: 96 Deville now throwing a P0171 and P0174 Codes.

    No I Havent. I will go check it now.

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, stick on fender vents
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    Re: 96 Deville now throwing a P0171 and P0174 Codes.

    You'll need to listen carefully with a mechanic's stethoscope to find the vacuum leak(s). If it is the overpressure valve, the intake manifold must be removed.

    http://lmgtfy.com/?q=cadillac+forums...ld+removal&l=1

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    basscatt's Avatar
    basscatt is online now Cadillac Owners Master
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    Re: 96 Deville now throwing a P0171 and P0174 Codes.

    you have a big vacuum leak somewhere -

    get a can of carb cleaner - attach the straw -
    spray it around all intake gaskets and hoses -

    when the idle speed increases - you found a leak -

  7. #6
    ralphieboy57 is offline Cadillac Owners Member
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    Re: 96 Deville now throwing a P0171 and P0174 Codes.

    Just letting you guy know you were right..... Its the Backfire Valve in the intake manifold. Big leak!. I have the intake out but where did you purchase the part at. Autozone and Pep Boys don't have it listed. And how much did it cost yah. Thanks

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, stick on fender vents
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    Re: 96 Deville now throwing a P0171 and P0174 Codes.

    Talk to Chris in Parts at Rippy Cadillac over there >>> tomorrow morning, business hours, EST (Wilmington, NC)

    Meanwhile look at your car, year model, engine, system in www.gmpartsgiant.com . Once you get to the correct parts text page you can click on the More Info tab to open a diagram keyed to the text page.

    Also - take a long, hard look at that PCV dirty air line - those rubber elbows rot out and crack with great regularity. Better safe than sorry. The Help! racks at large parts stores. If the plastic formed line is cracked, you can replace it with a proper length of reinforced fuel hose.

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