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Thread: '91 CV smog pump bypass create issue?

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    Member Hill185's Avatar
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    Default '91 CV smog pump bypass create issue?

    Possibly a coincidence, however, I bypassed the smog pump as it was making a racket with the recommended bypass belt (5.0 EFI). Now the car runs pretty rough puttering and shuddering both at idle and acceleration for lack of a better term. Read previous posts where people have bypassed the smog pump without issue. I did not make any modification to the pump itself IE remove or alter any components. Has anyone else run into issues doing the same?

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    Lost and driftin' Arquemann's Avatar
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    From my understanding, on SEFI models the smog pumps also works as a vacuum pump. Maybe it's causing a vacuum leak when it's not running? (Purely speculation, I don't know how it'd operate)
    1985 Mercury Grand Marquis LS, "Maisa"
    1995 Chevrolet Caprice Classic STW, "Sally"

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    Member Hill185's Avatar
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    That was my fear as well

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    Lost and driftin' Arquemann's Avatar
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    Quote Originally Posted by Hill185 View Post
    That was my fear as well
    Should be easy enough to check if that's the case. Find the vacuum line going to the pump and plug it.
    1985 Mercury Grand Marquis LS, "Maisa"
    1995 Chevrolet Caprice Classic STW, "Sally"

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    Road Warrior Kodachrome Wolf's Avatar
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    There's a three way check valve up near the cruise control servo. Follow that line that tees off and goes down towards the smog pump and there should be another two way check valve. If either of those check valves have failed, it could be causing trouble. There is also supposed to be check valve setup for the smog pipes that come off the back of the cylinder heads and feed into the TAB/TAD solenoids on the passenger side of the engine. Might be worth checking to make sure that's not leaking by either. That can also be plugged off at the check valve with a sturdy vacuum cap and hose clamp.

    As you've said, plenty of folks have bypassed/deleted the pump without trouble, myself included.

    My Cars:
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  6. #6
    Beater gonna beat sly's Avatar
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    +1 plug the port on the vacuum T near the cruise servo or plug the vacuum line at the smog pump. Double check for broken vacuum lines along the way as well.

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