89 MYSTERY ISSUE WHEN WARM
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Thread: 89 MYSTERY ISSUE WHEN WARM

  1. #1
    FRESHMAN ROVER
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    89 MYSTERY ISSUE WHEN WARM

    Hello friends! Hoping to get a little help here. I've had a persistent problem with my 89 Rangie “misfiring” when warm. I put misfire in quotes because it’s not really a misfire but more like all cylinders shut down for a second under load.
    She starts right up and idles nicely. Runs pretty well for the first 4 miles or so but when it warms up (normal operating temp) it "misfires" under load-when I hit the throttle to get up a hill. The EFI light will stay off until it hits that shut-down stumble then it comes on until I clear it by removing a battery cable from the terminal. So far I've replaced the fuel pump, coil, coolant temp sensor, added a new alternator, distributor cap and rotor and still problem remains. I'm at the end of my rope of things to try. Any suggestions? Your help is very Much appreciated!











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  3. #2
    FRESHMAN ROVER
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    Re: 89 MYSTERY ISSUE WHEN WARM

    Could be worth looking the TPS (throttle position sensor) it should competently bring mixture up under acceleration demand, if not the motor can feel like it falls flat on it's face as you ask for more torque.

    Also check vacuum to distributor as it will affect this area of running.

  4. #3
    SENIOR ROVER
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    Re: 89 MYSTERY ISSUE WHEN WARM

    your failure is typical of a failing speed sensor aka cruise control transducer. it governs the engine by means of cutting a whole bank thus reducing power.
    2k p38 4.6
    95 lwb 4.6
    01 d2 4.0

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  6. #4
    FRESHMAN ROVER
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    Re: 89 MYSTERY ISSUE WHEN WARM

    Thanks for the reply! Do you think the TPS would be affected by engine temp?

  7. #5
    FRESHMAN ROVER
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    Re: 89 MYSTERY ISSUE WHEN WARM

    Quote Originally Posted by 95classiclwb View Post
    your failure is typical of a failing speed sensor aka cruise control transducer. it governs the engine by means of cutting a whole bank thus reducing power.
    The Cruise control has never worked since I've owned her in the last 6 years.

  8. #6
    FRESHMAN ROVER
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    Re: 89 MYSTERY ISSUE WHEN WARM

    No I doubt it would change with temperature, just that during cold start and warming it'll be running richer in response to input from water temperature report to ecu. That will just make it accelerate more readily but the effect of this on fuel map will diminish as temp climbs to normal.

    Normal temp running will run quite lean on low torque demand, supplemented by giving richer mix in response to bigger throttle demand. It gets this from TPS, so if faulty it may not supplement sufficiently to give smooth response on demand. You may be able to increase speed by backing off demand and letting rpm climb gently, but obviously faced with a slope you can't do this.

    It may be worth checking against spec to see if it's not giving you correct response to eliminate it.

  9. #7
    FRESHMAN ROVER
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    Re: 89 MYSTERY ISSUE WHEN WARM

    What code does the check engine light produce. I see you say you cleared the codes, but never say what the codes are. the codes may give a good clue as to where to start troubleshooting.
    Simon

    95 Range Rover Classic

  10. #8
    SENIOR ROVER
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    Re: 89 MYSTERY ISSUE WHEN WARM

    Quote Originally Posted by miggy View Post
    The Cruise control has never worked since I've owned her in the last 6 years.
    if you read the rave section on fuel injection you will find where the transducer is needed for engine performance including idle and not necessarily for cruise control.
    another great read is britishv8.org
    2k p38 4.6
    95 lwb 4.6
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  11. #9
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    Re: 89 MYSTERY ISSUE WHEN WARM

    Do you think you'd get a cross check on transducer from other functions?

    Mine on a ZF 4 speed brings the torque converter lockup in at exactly 51 mph bang on every time, is this read from transducer do you think?

    If thats the case, you'd at least get a confirmation it was working.

  12. #10
    SENIOR ROVER
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    Re: 89 MYSTERY ISSUE WHEN WARM

    Quote Originally Posted by RRLondon View Post
    Do you think you'd get a cross check on transducer from other functions?

    Mine on a ZF 4 speed brings the torque converter lockup in at exactly 51 mph bang on every time, is this read from transducer do you think?

    If that's the case, you'd at least get a confirmation it was working.
    no, your transmission is mechanical thus transducer does not interfere with transmission operation. if you wanted to change shifting points one of your adjustments is the throttle kick down cable, more in depth changes and adjustments can be performed at the valve body. that is more of an expert situation.
    2k p38 4.6
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  13. #11
    FRESHMAN ROVER
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    Re: 89 MYSTERY ISSUE WHEN WARM

    Quote Originally Posted by 76FJ55 View Post
    What code does the check engine light produce. I see you say you cleared the codes, but never say what the codes are. the codes may give a good clue as to where to start troubleshooting.
    Simon it's an 89 no codes just efi light.

  14. #12
    FRESHMAN ROVER
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    Re: 89 MYSTERY ISSUE WHEN WARM

    Quote Originally Posted by 95classiclwb View Post
    no, your transmission is mechanical thus transducer does not interfere with transmission operation. if you wanted to change shifting points one of your adjustments is the throttle kick down cable, more in depth changes and adjustments can be performed at the valve body. that is more of an expert situation.
    I'd not taken that into consideration in my assessment Thankyou 95classiclwb as you're entirely right, it has no electronic management. We also run a ZF5HP24 in another vehicle which is electronic control with adaptable strategy in shift pattern.

    It is uncannily accurate at 51mph though. We have a route into London and our home with a 50mph speed restriction for some miles and you can just feel it dropping in and out if you're just trying to stay around there.

    Question for the OP, does it take a quick full throttle blip when warmed up but stationary? Or does it give the flat spot like that too?

  15. #13
    SOPHOMORE ROVER
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    Re: 89 MYSTERY ISSUE WHEN WARM

    Does this happen at similar throttle? It's easy to test the TPS with a meter.
    Kevin
    88 RRC "Audrey"

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