4.9l stumble
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HT4100 4.1, 4.5, 4.9 Discussion, 4.9l stumble in Cadillac Engine Technical Discussion; I have 92 4.9l . My problem: Surging/Stumbling/Hesitation upon light acceleration. What I have done so far: replaced bad/old vacuum ...
  1. #1
    wanobi is offline Cadillac Owners Member
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    4.9l stumble

    I have 92 4.9l .

    My problem: Surging/Stumbling/Hesitation upon light acceleration.

    What I have done so far:

    replaced bad/old vacuum lines
    cleaned TB blades and egr tubes
    got my hands on a data reader
    had a intermitting signal from the map. connector was not tight.

    information I have:

    when the engine starts its Surging/Stumbling/Hesitation routine I noticed that my left bank injector pulse time is flucuating. The right bank stays constant or smoothly increases as I accelerate.

    Questions:

    1. What controls the injector pulse times?
    2. Which is the left bank?
    3. What else could be causing the Surging/Stumbling/Hesitation

    TIA,

    Rod

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  3. #2
    carnut is offline Cadillac Owners Master
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    Re: 4.9l stumble

    Left bank is the one closest to radiator.

  4. #3
    carnut is offline Cadillac Owners Master
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    Re: 4.9l stumble

    Try some SEAFORM brand injector cleaner. Sounds like dirty injectors. The ECM gets pulse width info from a few sources, but the TPS angle is the main one.

  5. #4
    HUF's Avatar
    HUF
    HUF is offline Cadillac Owners Connoisseur
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    Re: 4.9l stumble

    Four injectors on every side have a common connector (two connectors totally). I would make sure they are fine (disconnect/reconnect). The ECM (powertrain computer) has drivers for injectors. Those drivers might be bad. Also check the resistance of the injectors. You can do that right on the connectors I have mentioned. They should be around 17 ohm.

  6. #5
    wanobi is offline Cadillac Owners Member
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    Re: 4.9l stumble

    thanks for the info. I am going to try the injector cleaner. but first I will ohm out the injectors..the connectors for each bank. do they connect to the ECM or do they plug into another connector before getting there. I guess I could just follow the wires?

    I will post back with my findings.

    Rod

  7. #6
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    HUF
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    Re: 4.9l stumble

    Quote Originally Posted by wanobi View Post
    thanks for the info. I am going to try the injector cleaner. but first I will ohm out the injectors..the connectors for each bank. do they connect to the ECM or do they plug into another connector before getting there. I guess I could just follow the wires?

    I will post back with my findings.

    Rod
    On the engine side a connector is wired to the individual injectors, which are represented by VERTICAL pairs of pins. You will figure out, I am sure.

  8. #7
    NickySantoro is offline Cadillac Owners Fanatic
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    Re: 4.9l stumble

    Since each FI bank is fused separately, you might want to check for corrosion at the fuse block.

  9. #8
    wanobi is offline Cadillac Owners Member
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    Re: 4.9l stumble

    Update: I ohm'd out the injectors and they all read 17.5 give or take an ohm. I kept wanting to lean towards the EGR system, so I bit the bullet and bought a new EGR solenoid. Performed the idle relearn procedure and it now is idling smoothly. Took it for my test drive and no hestitation or stumble. Now for real world driving to see if it is truly fixed.

    Rod

  10. #9
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    HUF
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    Re: 4.9l stumble

    Quote Originally Posted by wanobi View Post
    Update: I ohm'd out the injectors and they all read 17.5 give or take an ohm. I kept wanting to lean towards the EGR system, so I bit the bullet and bought a new EGR solenoid. Performed the idle relearn procedure and it now is idling smoothly. Took it for my test drive and no hestitation or stumble. Now for real world driving to see if it is truly fixed.

    Rod
    Glad the fix was an easy and cheap one! Check the resistance of your injectors every year. So far they are good.

  11. #10
    wanobi is offline Cadillac Owners Member
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    Re: 4.9l stumble

    just got home from work. If it still has the hesitation/stumble its not doing it enough to make me think otherwise. Did have something new happen once I got home and put the car in park.

    Heard a clunk sound and the car kinda lurched, but it was in park. It did it twice before I turned the car off. I have a gloom and doom feeling coming on. Please tell me I'm wrong, unless it's the truth.

    TIA

    Rod

  12. #11
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    HUF
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    Re: 4.9l stumble

    Quote Originally Posted by wanobi View Post
    just got home from work. If it still has the hesitation/stumble its not doing it enough to make me think otherwise. Did have something new happen once I got home and put the car in park.

    Heard a clunk sound and the car kinda lurched, but it was in park. It did it twice before I turned the car off. I have a gloom and doom feeling coming on. Please tell me I'm wrong, unless it's the truth.

    TIA

    Rod
    Might be transmission sprag...

  13. #12
    wanobi is offline Cadillac Owners Member
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    Re: 4.9l stumble

    what is transmission sprag??

  14. #13
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    Lithorian is offline Cadillac Owners Enthusiast
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    Re: 4.9l stumble

    how much money you got? cuz its time for a rebuild.

  15. #14
    NickySantoro is offline Cadillac Owners Fanatic
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    Re: 4.9l stumble

    OP,
    Pull the distributor cap and check the wiring harness and connections at the ignition control module for looseness or corrosion. Is the problem more pronounced when the engine is hotter?

  16. #15
    wanobi is offline Cadillac Owners Member
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    Re: 4.9l stumble

    ok, last update. changed plug, plug wires. distributor cap and rotor button. So far all seems well. Driven the car about 70 miles a day for a week and no major complaints. Car is idling about 100 rpms to high but I can live with that.

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