Another difficult to start T3

Discussion in 'T3 & T4 Tech Help Clinic' started by Michael@92, Dec 27, 2017.

  1. Michael@92

    Michael@92 New Member

    Messages:
    19
    Location:
    Sydney
    Just back to this one for a moment – I think we might have Bus doing something similar.

    Have been reading the recent posts on this issue - which are helpful - but the issue we have is a little different.

    Have been looking over a friends newly purchased 82 air-cooled T3. (– purchased on my advice which might be the problem!!! ) Their Bus starts fine from cold every time, runs fine, idles well and generally behaves itself. However – when they try to restart it after it has been running for a while it is exceedingly difficult.

    The Bus will crank over for perhaps 10 – 15 seconds – then it sounds like it wants to catch but it will just chug chug chug while puffing out a little black smoke – (running rich? ) and then seems to clear its throat with another puff of smoke ( black ) then goes back to running normally.

    It seems like the Cold Start Valve might be operating when warm and effectively over fuelling the engine – like a stuck choke? Is it sensible to assume the Temperature Sensor might not be working correctly?

    Does this Sensor control the Cold Start Valve?

    Would it be worth trying to start the engine while warm with the Cold Start Valve disconnected?

    The other thought I had was the Auxiliary Air Valve might be playing or not playing a role?

    Anyone have any bright ideas or experience on this one?

    Thanks in advance….

    Seasons best to all,

    Michael
     
  2. cbus

    cbus Well-Known Member

    Messages:
    10,437
    Location:
    sunshine coast
    Think diagnosis is correct.
    May try with valve disconnected as mentioned to assess.
    Another thought is leaking injector ?? . Major guess. Check after eliminating the more obvious causes.
    Long shot but try some good fuel to clean out or a dose of injector cleaner.
    Don't overdose it tho. I suspect I stuffed a pump by overdosing and allowing to sit with it in tank for a long time ;)
     
    Syncro27 likes this.
  3. Grantus

    Grantus Well-Known Member

    Messages:
    13,713
    Location:
    Southern ACT
    Sounds like the symptoms of a failed temp sensor.:rolleyes:

    Replacement is a worthwhile cheap starting point, and a 90 second job. ;)
     
    David H likes this.
  4. tillis

    tillis Active Member

    Messages:
    139
    Location:
    gold coast
    How did you go? If still no luck have you checked that the spark plugs are the right heat range? Plugs too cold will foul
     
  5. AC-T3

    AC-T3 Well-Known Member

    Messages:
    765
    Location:
    Woy Woy
    Agree with cbus and grantus and would throw in a faulty fuel pressure regulator which when the diaphragm fails can send raw fuel up the vacuum feed line into the plenum. All 3 would also lead to awful fuel consumption. The auxiliary air flow regulator uses an electrically heated bi-metallic strip and residual engine heat so don't think it would be part of the problem. Good luck, and would like to hear where you source a T2 sensor. Only ones I can find are the stainless steel KK brand from China via the good old USA.
     
  6. Michael@92

    Michael@92 New Member

    Messages:
    19
    Location:
    Sydney
    Thanks for all the great advice and ideas everyone – really helpful.

    Working on the basis that simple cars have simple problems think we will start with the temp sensor.

    Have ordered a replacement from Bus Depot – as their description says –

    “Ours is the only one made from stainless steel with a brass electrical connector rather than tin. Better AND cheaper than the original Bosch was when last available.”

    As it is on the internet it MUST be true. It was also the only one we could easily find in stock. ( The shipping costs more than the part !! )

    As the Bus only displays a warm start issue and has no other symptoms once running and driving - my thinking leads me back to the starting cycle. My understanding is the Cold Start Valve only pumps while the engine is cranking over.

    The fuel consumption is normal – which leads me away from the fuel pump regulator or a leaking injector, the spark plugs are correct – no missing once it is running. It doesn’t blow any smoke – of any colour.

    Will report back presently.

    By the way – where is the sensor located?

    Thanks again for all the help.

    Michael
     
  7. AC-T3

    AC-T3 Well-Known Member

    Messages:
    765
    Location:
    Woy Woy
    It;s under the intake runner for number 3. Real mongrel of a position to get at but thats where it is.

    Not saying anything against the Chinese version as it seems to be all thats available right now, is new to the market and just might be the bees knees.
     
    Last edited: Dec 29, 2017
  8. cbus

    cbus Well-Known Member

    Messages:
    10,437
    Location:
    sunshine coast
    Guessing you should be able to back probe a connection to test temp sensor values ?
     
  9. AC-T3

    AC-T3 Well-Known Member

    Messages:
    765
    Location:
    Woy Woy
    Disconnect sensor, then

    T2 Sensor Values.png
     
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  10. Grantus

    Grantus Well-Known Member

    Messages:
    13,713
    Location:
    Southern ACT
    Ooo...:oops: Further to my last post referring to a 90 second job - well it is, on a water cooled T3, but with Rob’s advice, it may take a little longer on the air cooled T3. o_O
     
  11. Barry

    Barry Well-Known Member

    Messages:
    2,153
    Location:
    Abbotsford NSW
    Oil temperature -10C :eek:
     
  12. cbus

    cbus Well-Known Member

    Messages:
    10,437
    Location:
    sunshine coast
    Victorian specs ;)
     
  13. Grantus

    Grantus Well-Known Member

    Messages:
    13,713
    Location:
    Southern ACT
    Only in the Victorians snowfields, in the dead of winter perhaps?:rolleyes:
     
  14. cbus

    cbus Well-Known Member

    Messages:
    10,437
    Location:
    sunshine coast
    Or Canberra :)
     
    syncro likes this.
  15. Grantus

    Grantus Well-Known Member

    Messages:
    13,713
    Location:
    Southern ACT
    Frosty mornings, yes.....but only occasionally -10 degrees! ;)

    5F2D2535-D686-4AF2-ACF6-1686A842ADD2.jpeg
     
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  16. cbus

    cbus Well-Known Member

    Messages:
    10,437
    Location:
    sunshine coast
    Stabilising the contents to their new environment ;)
     
  17. Dapom

    Dapom Well-Known Member

    Messages:
    568
    Location:
    Brisbane
    Hey :)
    I would try hot start with the csv disconnected. If that sorts the problem then you know it’s either the csv or more likely the thermo time switch by intake runner to the left of the csv :)
    I think you’re right re it not being leaky injector/pressure reg. Having said that, after going through a long process getting my l-jet 83 running properly I know that nothing is a given lol
     
    David H likes this.
  18. AC-T3

    AC-T3 Well-Known Member

    Messages:
    765
    Location:
    Woy Woy
    Me thinks both thermo time switch and cold start valve are working sort of OK. Starts cold and runs good, but when hot cranks for 10 - 15 seconds before finally firing up with black smoke. Try this simple test (OK it is for the deep north):

    Thermo Time Switch.png
    Something is telling the ECU that engine is cold.
     
    syncro likes this.
  19. AC-T3

    AC-T3 Well-Known Member

    Messages:
    765
    Location:
    Woy Woy
    Now thats one big crate of wine (going by the sticker on the right).
     
  20. Michael@92

    Michael@92 New Member

    Messages:
    19
    Location:
    Sydney
    .....aaahhh the thermo time switch test is interesting... great idea - thank you.

    No surprise the sensor is under number 3 on the cylinder head - I expect this must be about the hottest part of the engine.

    I did see an article where an original Bosch sensor unit was tested against one of these new stainless steel units. It involved a stove, cooking pot of canola oil, a thermometer, an ohmmeter with the two sensors heated, measured and graphed. Doubt my wife would find this to be a sensible use of the kitchen.....


    upload_2017-12-30_13-10-52.png
     

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