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1988 RR 3.5 EFI Auto Idling Issues

Discussion in 'Engines' started by dougc, Jun 6, 2021.

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  1. dougc

    dougc Member

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    Hi

    I am experiencing a problem with my 1988 3.5 EFI auto in a RR Classic.

    When starting the engine from hot the revs are often erratic and dip down and when putting it in gear the engine sometimes stalls. I have checked all of the air hoses and changed where necessary. The engine runs fine after a short while and at any other time.

    I would be grateful for any advice tas to what might be causing this problem and how to resolve it.

    Thanks

    Doug
     
  2. Ratae

    Ratae Well-Known Member

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    Hot wire or flapper?
     
  3. dougc

    dougc Member

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    Flapper.
     
  4. discool

    discool Well-Known Member

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    Had similar with my 3.5 it was found the crankcase breather was blocked, so unscrew the flame trap and hose to the plenum and soak in petrol, better still replace the flame trap.
    Stalling is very inconvenient when u have an auto :)
     
  5. discool

    discool Well-Known Member

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    For your info, hot wire engines were only fitted to the 3.5 disco 1.;)
     
  6. Ratae

    Ratae Well-Known Member

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    Factory fitted, yes.
    But with big boy's meccano kits you never know what's been fitted later so safer to ask :)
    Replacing the 4CU & flapper with the Hotwire stuff appears to be a pretty standard conversion.
     
  7. Ratae

    Ratae Well-Known Member

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    ^^^^Ditto. An utter PITA when low speed manoeuvering.
    With mine the oil passageway in the plenum was also blocked solid. The metal pipe into the plenum that the breather hose pushes onto is an interference fit & can be pulled out - a bit of heat might help.
    The internal passage runs across the front of the plenum from left to right (as viewed from inside the car facing forward) before a 90 deg turn into the plenum on the right of the throttle butterfly.
    Mine was so packed it need a twist drill operated by finger power to clear it followed by a good squirting of carb cleaner - prop the butterfly open & push a clean lint-free rag in far enough to soak it up.
    Smear of hylomar on the pipe & push back into place.
    Another consequence of breather blockage is the crankcase pressurising which results in oil leaks from all sorts of interesting places!

    For the Flapper
    Also clean the area where the butterfly closes & check that the butterfly doesn't fully close. There must be a small airgap at the bottom as these don't have a stepper motor.
    Maximum of 0.05mm (0.002"). Adjusted by use of the stop adjustment screw against the stop lever. (The screw is a tiny allen headed grub screw)
     
    Last edited: Jun 7, 2021
  8. dougc

    dougc Member

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    Thanks for your responses. Would a blocked crankcase breather or plenum oil passageway only cause erratic low idling when restarting the engine from hot and not any other time?
     
  9. discool

    discool Well-Known Member

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    With my 3.5 the idle was always sowing machine smooth, smooth that thought that the engine had stopped, (unlike my 3.9 disco), but with in 10 minutes of the running and usually in traffic or at a junction the 3.5 engine would stall, but no problems out on the open road.
    Later in the 3.5s life the efi ecu had issues which affecting starting, but that’s another story.
     
  10. Ratae

    Ratae Well-Known Member

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    4CU ecus!

    Can be a total pain. IIRC I'm currently on my 3rd since buying the car in 1994. That said, when they go they go & the car either won't run at all or runs rough as a rough thing. Substitution with a known good one is the easiest check but they're not as common on ebay etc as they used to be.
    I must get around to sending one of mine off for repair to have as a spare to back-up the one good spare I've got & which lives in the car.

    Sounds like your problem is air related - as in not enough after the extra air valve has closed as the engine warms up.
    Also manifests with too much air if the plenum to extra air valve hose has fallen off or has split - which my result in it not starting/running at all. This 'C' shaped hose is ERC9117 and whilst they are available they seem to be old stock & don't last long before they split at the ends.
     
    Last edited: Jun 8, 2021
  11. Ratae

    Ratae Well-Known Member

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    You'll need to check & clean yours to eliminate it as a possible cause.
    If that solves the problem you have your answer, if it doesn't it's elsewhere.
     
  12. dougc

    dougc Member

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    Just an update. I checked the plenum oil passageway and replaced the flame trap which seems to have resolved the issue (hopefully).

    Thanks for all your help.
     
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