Where did the oil pressure go on my 308 GT4 | FerrariChat

Where did the oil pressure go on my 308 GT4

Discussion in '308/328' started by magaoidh, Jan 10, 2010.

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  1. magaoidh

    magaoidh Karting

    May 12, 2009
    220
    I have had the car up on stands for months now giving it a thorough inspection and repairs as necessary!
    Started the engine after a rekit of the carbies and I have the engine purring like a ***** cat,but the oil pressure gauge is not indicating even though the oil pressure sender is new!
    How can I test to find out if it is the gauge or the sender???When I turn the ignition on the gauge needle stays at rest!
    I have read that there is an oil pressure switch/valve which may have an influence too but where is it?
    Geoff
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,785
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #2 Steve Magnusson, Jan 10, 2010
    Last edited: Jan 10, 2010
    Unplug the wire from the pressure sender and touch it to ground with the key "on" -- if the gauge is working, the needle should swing to the "max" side when that wire is grounded (to the engine).

    What year/version 308GT4? -- I believe the oil pressure switch (and its corresponding red warning light in the gauge) was not introduced until the later years.
     
  3. magaoidh

    magaoidh Karting

    May 12, 2009
    220
    Steve its a 1979 model and has the red warning light in the gauge.
    I have tested as suggested and the needle moved to the max. and the red light came on!
    So that proves the gauge is okay,as the oil pressure sender is new its possible it is faulty, can I test that?
    Or could it be the oil pressure valve that is faulty,spring broken etc.?
    Thanks for the assist,Geoff
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,785
    30°30'40" N 97°35'41" W (Texas)
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    Steve Magnusson
    #4 Steve Magnusson, Jan 10, 2010
    Last edited: Jan 10, 2010
    The red warning light should be "on" when the key is "on" and the engine is not running. If the red light stays "on" when the engine is running, that would be a sign that you really don't have any oil pressure, and would need to look at things like broken/blocked oil pressure regulator, blocked oil filter, you forgot to add oil ;), etc. -- does the red light go "off" when the engine is running? If it does, it's almost a certainty that the (new) oil pressure sender is bad (as you've already proved that the gauge works, and would give a reading if the pressure sender resistance went down as the oil pressure went up, as it should). If the red light doesn't go off when the engine is running, that's a much more serious issue (and shut off the engine immediately until resolved).
     
  5. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    13,551
    San Carlos, CA
    Full Name:
    Mitchell Le
    If you truly believe you have oil pressure in the engine and it is either the gauge or the sender that is bad, then by all means continue with trouble shooting.

    If you are not sure if you even have oil pressure in the engine, then make sure there is adequate oil pressure before you go on. When the engine is all brand spanking new and there is no oil in the oil circuit, you have to prime the oil pump before it can even pump out anything. I don't know what else you did to your engine so I can't say.
     
  6. PV Dirk

    PV Dirk F1 Veteran

    Jul 26, 2009
    5,401
    Ahwatukee, AZ
    If you still have the old unit available swap it back in and test.
     
  7. magaoidh

    magaoidh Karting

    May 12, 2009
    220
    Yes,I do have the old pressure sender and the warning light does go out on start up, so there is oil pressure I believe,its not a new motor BTW.
    In comparison the old unit and new unit differ as far as resistance is concerned.Using a multimeter, reading between the sender lead connector and the "brass" casing I get open circuit with the new sender and around 12ohms with the old unit.
    Can anyone who has a working sender do that reading for me?I am sure the new sender was indicating on the pressure gauge initially.
     
  8. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,785
    30°30'40" N 97°35'41" W (Texas)
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    Steve Magnusson
    #8 Steve Magnusson, Jan 10, 2010
    Last edited: Jan 10, 2010
    The "open" (i.e., infinite resistance) on the new sender corresponds well with your problem of having no motion of the needle in the gauge, but the 12 ohms for the old sender (at zero pressure or at a normal operating pressure) seems much too low compared to this good data previously posted by RJay (Bob):

    http://ferrarichat.com/forum/showthread.php?t=103015
     
  9. brook308

    brook308 Formula Junior

    Oct 19, 2007
    346
    SS Coast, Australia
    Full Name:
    George
    With no oil pressure, engine off my sender measures approx 9K ohms or 9000 ohms to ground.
     
  10. yelcab

    yelcab F1 World Champ
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    Nov 29, 2001
    13,551
    San Carlos, CA
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    Mitchell Le
    Did you disconnect all the wiring before you make the measurement?
     
  11. magaoidh

    magaoidh Karting

    May 12, 2009
    220
    Thanks for the thread by RJay that is very much my problem,hmmmmm I believe the old unit reading was 120 ohms so maybe after injecting with WD-40 I will try it again.The new unit I was thinking about unbuttoning anyway,Thanks Guys!
     
  12. mike996

    mike996 F1 Veteran

    Jun 14, 2008
    6,871
    Full Name:
    Mike 996
    Check the REAL oil pressure first with a mechanical gauge OR just remove the sender and hand someone crank the engine. The latter will be messy but it will tell you if you have oil pressure. THEN fool around with troubleshooting from that point. THe most important thing to know is IF you have oil pressure. Checking sending units and gauges doesn't tell you a darned thing about the most important item...do you have oil pressure? ;)
     
  13. blainewest

    blainewest Formula Junior

    Aug 26, 2005
    729
    Kelowna, BC
    Full Name:
    Blaine W
    Another way you can check if there's oil pressure is to remove the oil filler cap, have someone start it up and watch the cam caps you can see through the filler hole. You should see oil coming out from under the cam caps as the cam spins.
     
  14. gerritv

    gerritv Formula 3

    Jun 18, 2001
    1,400
    St Catharines
    Full Name:
    Gerrit
    There have been cases where the wrong sender is in the box. Take the sender out and see if there is a hole in the bottom. If not, it is a temperature sender, not a pressure sender.

    BTDT,

    Gerrit
    http://dino308gt4.com
     
  15. magaoidh

    magaoidh Karting

    May 12, 2009
    220
    #15 magaoidh, Jan 13, 2010
    Last edited: Jan 13, 2010
    Okay,I put the old one back in,it was reading 300 ohms inert.After starting up there was not much happening so I dismantled the new faulty one and after much fiddling got it reading 300 ohms,fitted it to the car and hey presto I have pressure registering.Low though!
    Being a newer type there is a copper tab which has to be doubled over to make contact with the variable resisitor effectively! That was all I could see out of kilter.
    Now that oil pressure relief valve anyone know if increasing the number of shims increases the oil pressure?
    Thanks so far, Geoff
     
  16. eurogt4

    eurogt4 Karting

    Apr 15, 2006
    243
    Sacramento, CA
    Full Name:
    Mike
    I think you should find out what your actual pressure is with a mechanical guage before you adjust the pressure relief valve. I believe adding shims to the spring will raise the maximum pressure. Removing those shims and adding copper washers to the cap will lower maximum pressure. Remember that the pressure relief valve only controls your maximum pressure, not the minimum.
     

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