'94 Deville4.9L idles rough ! - Page 2
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View Poll Results: 4.9L rough idle

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HT4100 4.1, 4.5, 4.9 Discussion, '94 Deville4.9L idles rough ! in Cadillac Engine Technical Discussion; Originally Posted by Night Wolf my 4.9 can be rough at an idel.......but as soon as the rpm comes it, ...
  1. #16
    ga_caddy is offline Cadillac Owners Member
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    Re: '94 Deville4.9L idles rough !

    Quote Originally Posted by Night Wolf
    my 4.9 can be rough at an idel.......but as soon as the rpm comes it, she smooths out and purrs really nice......it's just one of those 4.9 things ya know? since there isn't much that goes wrong with these enignes, we gotta have something.....it gives the car that nice classic muscle car rumble at idel attitude
    Well that is when mine is doing. The EGR Valve was broken and the passages were blocked but that is all fixed. All the vacuum lines were replaced. The TPS got replaced because I broke it. There was a vacuum leak at the rubber hoses on either end of the PCV line.

    The idle is a lot smoother now but I am still not happy. I'm going to take it to a friends shop sometime soon to put it on the scope. Hopefully when that is done we'll be able to pinpoint the cause. I have a funny feeling it's fuel related.........

  2. #17
    2Clown2 is offline Cadillac Owners Member
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    Re: '94 Deville4.9L idles rough !

    Took the Vapor line off at the Canister and applied vacuum to the tank. It will not hold any. How does the gas tank vent, if this Vapor line is the only line to it?
    I will test the Canister and Purge Sol first thing.

  3. #18
    ga_caddy is offline Cadillac Owners Member
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    Re: '94 Deville4.9L idles rough !

    Quote Originally Posted by 2Clown2
    Took the Vapor line off at the Canister and applied vacuum to the tank. It will not hold any. How does the gas tank vent, if this Vapor line is the only line to it?
    I will test the Canister and Purge Sol first thing.
    OPERATION
    The Evaporative Emissions (EVAP) solenoid receives 12 volts from the fuse panel. The Powertrain Control Module (PCM) energizes the EVAP solenoid by grounding CKT 428. When the solenoid is energized, it allows the canister to purge. When a purge mode is commanded, stored fuel vapor is drawn into the inner dip tube through a calibrated orifice at the base of the tube. Any liquid trapped in the liquid well is also drawn into the inner dip tube through a smaller calibrated orifice. Fresh air is drawn into the canister at the top mounted vent.

    Under cold engine, "OPEN LOOP," or idle conditions, the solenoid is de-energized by the PCM, which closes the purge solenoid and blocks vacuum to the canister.

    The canister will be enabled (PCM energizes the solenoid) when:


    Coolant is above 80°C (176°F).
    Closed loop has been achieved for at least 30 seconds.
    The throttle switch is open.
    Vehicle speed greater than 10 mph.
    Engine speed above a threshold. OR
    Code P013, P017, P042, P043, P044, or P045 is present.
    If the solenoid is closed, (not receiving power or has a stuck plunger), the canister will not purge to the intake manifold. This will prevent the canister from purging fuel vapors and could result in a complaint of fuel odors coming from the engine compartment.

    FUNCTIONAL TEST



    Attach a hose to the fuel vapor port (from fuel tank) of the canister and attempt to blow through it. Air should pass into canister, If not, replace the canister.
    Disconnect the EVAP solenoid electrical connector, attach a hose to the upper port of the canister, and attempt to blow through it. Air should not pass into the canister. If air passes, replace the canister.
    Reconnect all purge hoses and the solenoid electrical connector.

  4. #19
    2Clown2 is offline Cadillac Owners Member
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    Re: '94 Deville4.9L idles rough !

    If I listen real carefully and watch the RPM's (PO11),trying to hold a steady 1500rpm, I can tell that it is doing the idle thing through-out the range. This cannot be good for the engine. The EVAP cannister checks good, so I too am ready to accept this rascall as "character" and live with it!

  5. #20
    semiauto is offline Cadillac Owners Member
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    rough idle

    My 1993 Eldorado 4.9 was idling really really rough. I found that the problem with it was the fuel pressure regulator.

  6. #21
    ga_caddy is offline Cadillac Owners Member
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    Re: rough idle

    Quote Originally Posted by semiauto
    My 1993 Eldorado 4.9 was idling really really rough. I found that the problem with it was the fuel pressure regulator.
    I'll look into the FPR. But for the most part the idle is much better now that I have cleaned the fuel injectors along with the rest of the things I have done.

    Thanks again to everyone for their help!!

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