Page 1 of 2 12 LastLast
Results 1 to 10 of 11

Thread: Surging 4.6 at idle and cold

  1. #1
    Join Date
    Jan 1970
    Location
    Gold Coast
    Posts
    1,937
    Total Downloaded
    0

    Surging 4.6 at idle and cold

    Got 4.6 in RRC that when it starts and cold dies then recovers over and over until warms. Gets progressively better. Runs fine uf push accelerator.

    I cant see a stepper motor/idle control on the motor.

    So after suggestions from anyone who knows this set up.

    Thanks in advance

    89 Orange Rangie UTE - our play thing - sadly now sold
    75 Rangie/Series/Hybrid - Bumblebee with a sting!!!!
    2012 RRS - The new touring vehicle

  2. #2
    Join Date
    Jan 2016
    Location
    Netherlands
    Posts
    882
    Total Downloaded
    0
    I guess your 4.6 has an older style intake to fit the rrc. Is it fuel injected and if so what system? Anyway, the first thought is that round plastic thing in the first picture with the brown and green wire, that is either a TPS or it is your idle air. Hard to see on the pics. It seems to be in line with the intake butterfly valve so that could suggest TPS.

    My second guess would be the device with the green plug and the rubber hose on the other side of the intake cover. I am not familiar with this setup though so these are only guesses.

    Cheers,
    -P

  3. #3
    Join Date
    Jan 1970
    Location
    Avoca Beach
    Posts
    13,981
    Total Downloaded
    0
    That is an old “ flapper” fitted to 3.5 until 1989.
    it does not have a stepper but a thermo time switch and a cold start injector in the side of the plenum.
    The thermo time switch can malfunction but most likely is that the cold start injector is drooling.
    disonnect the cold start injector and see what happens.
    Regards PhilipA

  4. #4
    Join Date
    Jan 1970
    Location
    Gold Coast
    Posts
    1,937
    Total Downloaded
    0

    Updated Pics and reply

    Thanks PhilipA

    The hose to the cold start injector on top right (left as look at it) of plenum was very cracked. When I replaced it there was no fuel pressure in the line vs manual that says there should be.

    I will test removing the plug to this injector - is see new they are about $1k form the UK - wow!

    Some better quality pics from a real camera not a phone
    DSC_0310.jpgDSC_0313.jpgDSC_0315.jpgDSC_0312.jpg

    89 Orange Rangie UTE - our play thing - sadly now sold
    75 Rangie/Series/Hybrid - Bumblebee with a sting!!!!
    2012 RRS - The new touring vehicle

  5. #5
    Join Date
    Jan 1970
    Location
    Gold Coast
    Posts
    1,937
    Total Downloaded
    0
    Quote Originally Posted by prelude View Post
    I guess your 4.6 has an older style intake to fit the rrc. Is it fuel injected and if so what system? Anyway, the first thought is that round plastic thing in the first picture with the brown and green wire, that is either a TPS or it is your idle air. Hard to see on the pics. It seems to be in line with the intake butterfly valve so that could suggest TPS.

    My second guess would be the device with the green plug and the rubber hose on the other side of the intake cover. I am not familiar with this setup though so these are only guesses.

    Cheers,
    -P
    Thanks yes it is the TPS
    Green plug rubber hose is a cold engine extra fuel injector - shown in manual for RRC v8s in late 1980's

    Computer - yet to look under the seat - there is an extra box on top of the large alloy normal RRC one.

    89 Orange Rangie UTE - our play thing - sadly now sold
    75 Rangie/Series/Hybrid - Bumblebee with a sting!!!!
    2012 RRS - The new touring vehicle

  6. #6
    Join Date
    Jan 1970
    Location
    Avoca Beach
    Posts
    13,981
    Total Downloaded
    0
    The hose to the cold start injector on top right (left as look at it) of plenum was very cracked. When I replaced it there was no fuel pressure in the line vs manual that says there should be.
    the injector is controlled byThe thermo time switch. I don,t know if it should hav
    e pressure all the time.
    another simple problem with rich running which is what it sounds like is the temp sensor. I am not sure whether the thermo time switch takes its readings from a temp sensor or not. If there is a temp sensor it should be at the front of the manifold with 2 wires to it. The one with only one wire just runs the gauge.
    it sounds like the ecu has a piggyback ecu to run the bigger motor so that complicates problem solving.
    regards PhilipA

  7. #7
    Join Date
    Jan 1970
    Location
    Gold Coast
    Posts
    1,937
    Total Downloaded
    0
    Quote Originally Posted by PhilipA View Post
    the injector is controlled byThe thermo time switch. I don,t know if it should have pressure all the time.
    another simple problem with rich running which is what it sounds like is the temp sensor. I am not sure whether the thermo time switch takes its readings from a temp sensor or not. If there is a temp sensor it should be at the front of the manifold with 2 wires to it. The one with only one wire just runs the gauge.
    it sounds like the ecu has a piggyback ecu to run the bigger motor so that complicates problem solving.
    regards PhilipA
    PhilipA thanks again

    Re Pressure - hose comes straight off the fuel rail to the cold start injector so I assume it has to be pressurized - manual says to depressurize first.
    Yes wiring diagram shows that (7) the cold start injector is on based on the signal from (8) the thermotime switch.
    Wiring.jpg

    A post elsewhere 3.5 efi V8 - cold start not working? - International Forum - LR4x4 - The Land Rover Forum
    says the following including just unplugging the cold start injector.

    "For a cold start (cold engine) on the flapper extra fuel is injected into the plenum chamber by the injector that sticks out of the side of the plenum (top centre on the drivers side. This is controlled by the thermotime sensor which is the front of the 2 sensors on the top of the inlet manifold. When the switch goes faulty the usual result is overfuelling which may cause starting/running problems. (The rearmost of the 2 sensors is the temp sensor & when that plays up it also usually causes overfuelling & is the cause of many mysterious running troubles for which the ECU is usually wrongly blamed) Generally the cold start injector serves little purpose in temperate climes & many just unplug the electrical leads from the injector. I did just that when I bought mine & it makes no apparent difference to the starting."

    89 Orange Rangie UTE - our play thing - sadly now sold
    75 Rangie/Series/Hybrid - Bumblebee with a sting!!!!
    2012 RRS - The new touring vehicle

  8. #8
    Join Date
    Mar 2008
    Location
    Bellarine Peninsula, Brackistan
    Posts
    5,309
    Total Downloaded
    0
    Blocked fuel return line at the fuel tank.

    DL

  9. #9
    Join Date
    Jun 2008
    Location
    Drouin East, Vic
    Posts
    2,590
    Total Downloaded
    0
    Looking at this thread has brought back memories of pouring money into one of these EFI systems trying to get it to run a Leyland 4.4 about 20 years ago.
    There appear to have been modifications made to the 3.5 flapper system to get it to run the bigger engine, you have hose barbs blanked off here there and everywhere and unless you know exactly what mods have been made you are in for a hard road getting it to do things like play nicely when cold. Did you do the installation, or have you inherited this setup from someone else who has made unknown mods?
    The cold start injector would never have actuated in a Gold Coast climate, if it is leaking / dribbling as Philip suggests then your best bet will be to disconnect the hose at the injector and permanently plug it. You wouldn't even miss it on a trip to the snowfields in Aus, more of a scandinavian winter thing.
    There was a bypass air valve that has been removed from your system, it sat on the horizontal plinth behind the ignition coil in your photo #2 in post #4, had a rotating valve that was actuated by a bimetal strip, a heating coil gradually closed the valve via electrical heat and then heat from the manifold kept it closed once the engine was warm. The valve bypassed the throttle butterfly to give increased idle RPM. The system on the Jaguar 4.2 of the same era had a bigger port in the valve which suggests that the amount of bypass air necessary is specific to the motor size. Presumably your engine has had some other sort of warm-up valve installed in place of this.

  10. #10
    Join Date
    Jan 1970
    Location
    Avoca Beach
    Posts
    13,981
    Total Downloaded
    0
    That’s the thermo time switch in Bosch speak.
    regards PhilipA

Page 1 of 2 12 LastLast

Tags for this Thread

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Search AULRO.com ONLY!
Search All the Web!