Rough 4th gear
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HT4100 4.1, 4.5, 4.9 Discussion, Rough 4th gear in Cadillac Engine Technical Discussion; Recent development, '91 Eldorado runs fairly well through 1-2-3 gears, but as soon as I shift into 4th gear, particularly ...
  1. #1
    collinsc is offline Cadillac Owners Member
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    Rough 4th gear

    Recent development, '91 Eldorado runs fairly well through 1-2-3 gears, but as soon as I shift into 4th gear, particularly at low rpms, the whole car shakes, almost like it is missing but only in one gear? The only other time I feel this kind of roughness is occasionally at idle the engine will run so roughly that the car feels like it is rolling back and forth just a tad.

    Throwing this code, only recently, also:
    E46 - Right to left bank fueling difference

    Is it possible for the engine to miss in only one gear? I'd really not like to think my tranny is going @ 42,000mi

    Thanks in advance for any information.

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    HUF's Avatar
    HUF
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    Re: Rough 4th gear

    I would first fix the problem which set that code. As far as I remember it was oxygen sensor related. The symptoms you described can be cause with a massive vacuum leak. A stuck open EGR valve can do that. Just my 0.02.

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    collinsc is offline Cadillac Owners Member
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    Re: Rough 4th gear

    I pulled the EGR off today and it seemed fine...Im thinking its clogged injector? although wouldn't that cause symptoms in other gears also? Im going to run a bottle of lucas injector cleaner through it tomorrow..

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    Re: Rough 4th gear

    The oxygen sensors are what tell the computer of the fueling difference. The computer compares the values of each sensor over a certain period of time. Most of the fuel system affects both left and right banks simultaneously so the only things individual to each cylinder are the injectors. And likewise the only sensors individual to each bank are the oxygen sensors. In short, I think its one or more injectors on one side of the engine. They do funny things when they're failing and sometimes go on and off under the conditions of their choosing. Something to do with being in 4th gear could be causing one or more to go out, or maybe it is just most noticeable when in 4th.

    I think you would have to have a vacuum leak on one of the intake gaskets to cause a R/L fueling difference. A leak anywhere else would affect both banks the same.

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    Re: Rough 4th gear

    Quote Originally Posted by collinsc View Post
    I pulled the EGR off today and it seemed fine...Im thinking its clogged injector? although wouldn't that cause symptoms in other gears also? Im going to run a bottle of lucas injector cleaner through it tomorrow..
    I would leave injectors alone for a while. I NEVER heard of any problem solved by simply using an injector cleaner. It is more like a "feel good" thing IMHO.
    Your car allows onboard diagnostics of oxygen sensors. Unfortunately, I got rid of my 1991 Seville FSM, so someone else will likely chime in with directions.

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    Re: Rough 4th gear

    Quote Originally Posted by collinsc View Post
    Recent development, '91 Eldorado runs fairly well through 1-2-3 gears, but as soon as I shift into 4th gear, particularly at low rpms, the whole car shakes, almost like it is missing but only in one gear? The only other time I feel this kind of roughness is occasionally at idle the engine will run so roughly that the car feels like it is rolling back and forth just a tad.

    Throwing this code, only recently, also:
    E46 - Right to left bank fueling difference

    Is it possible for the engine to miss in only one gear? I'd really not like to think my tranny is going @ 42,000mi

    Thanks in advance for any information.
    The moment you feel shaking may be associated with 3-4 shift but also woth TCC lock-up. When TCC is not locked existing engine problems (like stumbling) are smoothed out with transmission. Things change when TCC is locked-up. That's when engine stumbling will be more noticeable. Idle is another condition under which any miss or stumbling is noticeable because the RPM is so low. My advice again is addressing the existing DTC which is related to the oxygen sensors.

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    Re: Rough 4th gear

    Quote Originally Posted by Sevillian273 View Post

    I think you would have to have a vacuum leak on one of the intake gaskets to cause a R/L fueling difference. A leak anywhere else would affect both banks the same.
    Yup, good call Sevillian. My money is on intake manifold gaskets.

    It's probably happening all the time. It's just that you can feel it more in 4th gear because the torque converter is locked, transmitting the vibrations more. Do you have a rough idle as well?

    edit: I suck, I just now saw that the idle is also rough.

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    collinsc is offline Cadillac Owners Member
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    Re: Rough 4th gear

    I wonder how possible of a job the intake manifold gaskets would be for me and my fairly mechanically inclined father. I'd like to avoid getting raped at a mechanic considering the gasket looks to be only $20.

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    Re: Rough 4th gear

    Collinsc, do you loose any coolant?

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    Re: Rough 4th gear

    Dont jump to conclusions just yet. Intake gaskets are a worst-case scenario for your symptoms. Injector failure is VERY common on these engines and is the most likely culprit in my opinion. At the very least, you should check the resistance of each injector with a digital voltmeter. You're looking for 12-17 ohms. 2nd most likely cause as HUF said, is a bad oxygen sensor sending false info to the ECM. I just dont think thats very likely at 40K but sh*t happens. They are cheap and easy to replace. In my opinion, replacing them is easier even than checking the injectors with a meter. Recommended change interval is 30K I believe for the o2's. I'll dig up some FSM scans and post them shortly...

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    Re: Rough 4th gear




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    Re: Rough 4th gear

    Here is chart A-5-A as mentioned in the above trouble tree. It also describes the 'Injector Drop Test' which I suggest you do. It will pin point the offending injector if that is your problem. Its very easy and you dont even have to open the hood!




  14. #13
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    Re: Rough 4th gear

    Quote Originally Posted by Sevillian273 View Post
    Dont jump to conclusions just yet. Intake gaskets are a worst-case scenario for your symptoms. Injector failure is VERY common on these engines and is the most likely culprit in my opinion. At the very least, you should check the resistance of each injector with a digital voltmeter. You're looking for 12-17 ohms. 2nd most likely cause as HUF said, is a bad oxygen sensor sending false info to the ECM. I just dont think thats very likely at 40K but sh*t happens. They are cheap and easy to replace. In my opinion, replacing them is easier even than checking the injectors with a meter. Recommended change interval is 30K I believe for the o2's. I'll dig up some FSM scans and post them shortly...
    It is much easier to check the resistance of the injectors on the common connector (one per bank) than on an individual injector. Just follow wiring and you'll see the connector.

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    Re: Rough 4th gear

    Quote Originally Posted by HUF View Post
    It is much easier to check the resistance of the injectors on the common connector (one per bank) than on an individual injector. Just follow wiring and you'll see the connector.
    I agree, but if there is a fault in the wiring it will skew the results.

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    Re: Rough 4th gear

    Quote Originally Posted by Sevillian273 View Post
    I agree, but if there is a fault in the wiring it will skew the results.
    True, but if one gets normal resistances from the connectors within a minute, then one does not need to take measurements directly on the individual injectors, which is not that easy. Besides, the PCM gets the signal through the wiring.

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