Bad oil pressure sender unit? | FerrariChat
Buy

Bad oil pressure sender unit?

Discussion in '308/328' started by airdelroy, Jul 30, 2011.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, Skimlinks, and others.

  1. airdelroy

    airdelroy Formula Junior

    May 10, 2007
    420
    Austin, TX
    Full Name:
    Aaron Richardson
    #1 airdelroy, Jul 30, 2011
    Well, my oil pressure has recently taken a dive (85 euro). I put a mechanical gauge on and it reads normal (~75lbs). The electrical reads about 3 bar.

    So, I tested the the dash gauge by unplugging the sender and shorting the connector. The gauge moved to just past the last mark at 12 bar. I figured the sender was bad and I ordered part number 122592. This is a xref part I found in this thread:

    http://www.ferrarichat.com/forum/showthread.php?t=265812

    But when I get it put on today it still reads 3 bar and the mechanical is still reading normal.

    Could there be anything else causing this problem?

    thanks,
    Aaron
     
  2. miketuason

    miketuason F1 World Champ
    Owner Silver Subscribed

    Feb 24, 2006
    15,761
    Cerritos, CA.
    Full Name:
    Mike
    #2 miketuason, Jul 30, 2011
    What do you mean the electrical read 3 bar?
     
  3. airdelroy

    airdelroy Formula Junior

    May 10, 2007
    420
    Austin, TX
    Full Name:
    Aaron Richardson
    #3 airdelroy, Jul 30, 2011
    Oh, I also went back and re-tested the gauge by shorting it to the oil filter housing where the sender gets its ground. It again swung to the 12 bar mark.

    thanks,
    Aaron
     
  4. airdelroy

    airdelroy Formula Junior

    May 10, 2007
    420
    Austin, TX
    Full Name:
    Aaron Richardson
    #4 airdelroy, Jul 30, 2011
    The electrical gauge in the dash reads in bars, not lbs. It should read 6 bars.

    thanks,
    Aaron
     
  5. miketuason

    miketuason F1 World Champ
    Owner Silver Subscribed

    Feb 24, 2006
    15,761
    Cerritos, CA.
    Full Name:
    Mike
    #5 miketuason, Jul 30, 2011
    Ok, 3 bars seems a little low but, it depends on weather the engine is at normal op temp or cold and also the weight of of the oil you use. When it's cold during idle it should read to around 5 bars. and, at normal operating temp it should read around 1 to 2 bars during idle and around 6 bars under load. If not, then you might ahve iether another bad sending unit or faulty gauge.
     
  6. Paul_308

    Paul_308 Formula 3

    Mar 12, 2004
    2,345
    #6 Paul_308, Jul 30, 2011
    Last edited by a moderator: Sep 7, 2017
    Ferrari seemingly uses the metric unit kg/cm2 for oil pressure, which is 1.03 apart from 1 bar.

    NA gauges are in psi, 1 bar=14.7 psi, call it 15.

    IMHO oil pressure for a middle-aged engine with warm oil of 3-4 bar certainly can be normal.

    Back to the OP's question...I can understand the electrical gauge reading slightly low and the mechanical reading slightly high and nothing being wrong or worth worrying about. 3 bar and 75 psi aren't that far apart...3 might actually be 4 (60 psi).
    Image Unavailable, Please Login
    Image Unavailable, Please Login
     
  7. miketuason

    miketuason F1 World Champ
    Owner Silver Subscribed

    Feb 24, 2006
    15,761
    Cerritos, CA.
    Full Name:
    Mike
    #7 miketuason, Jul 30, 2011
    to be exact: atmospheric pressure is 14.7 psi. so,
    14.7 X 6 bars = 88.2 just a bit higher than normal.
     
  8. airdelroy

    airdelroy Formula Junior

    May 10, 2007
    420
    Austin, TX
    Full Name:
    Aaron Richardson
    #8 airdelroy, Jul 31, 2011
    I am checking the 2 gauges when the engine is cold, just started, and idling (although revving didnt change it). I have not yet heated up the engine with the new sender in place. I hope to do that today. However, with the old sender it would start out cold at about 3 bar (mechanical gauge reads 75). And when the engine was warmed up the electrical gauge would be about 0-1 bar while the mechanical would read ~35.

    I bought the mechanical gauge several years ago when I thought a reading of 2-3 bar from the electrical on a warm engine was too low (cold it would read 6 bar at idle). The mechanical gauge confirmed the electrical gauge was working fine then. Now the 2 gauges differ.

    thanks,
    Aaron
     
  9. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,507
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #9 Steve Magnusson, Jul 31, 2011
    Last edited: Jul 31, 2011
    Are you connecting the mechanical pressure gauge to the exact same port as the electrical sender, or somewhere else? If the same port, the suspicion has to still fall on the electrical side, but, if different places, things like an internally collapsed oil filter could cause different pressures to actually exist in different areas of the lubrication system.
     
  10. airdelroy

    airdelroy Formula Junior

    May 10, 2007
    420
    Austin, TX
    Full Name:
    Aaron Richardson
    #10 airdelroy, Jul 31, 2011
    Its attached in the same place at the same time as the electrical sender. I picked up a connector that allowed both to be attached. Cant seem to find the link in my notes for it though.

    As another data point if I just turn the key on without starting the motor (and tap the gauge :) ) it reads just short of zero. When I unplug the sender then the needs drops to where it sits with the key off.

    thanks,
    Aaron
     
  11. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,507
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #11 Steve Magnusson, Jul 31, 2011
    One thing you can try is to "replace" the gauge with a multimeter and measure it's resistance vs the pressure shown on the mechanical gauge. If the resistance values roughly follow the values that RJay posted in this thread:

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

    then you'd have to dig into the gauge and/or gauge wiring IMO. If the resistance values for both the old and new sender are the same (and don't match RJay's data), you could try getting a new, new sender -- just a thought...
     
  12. airdelroy

    airdelroy Formula Junior

    May 10, 2007
    420
    Austin, TX
    Full Name:
    Aaron Richardson
    #12 airdelroy, Jul 31, 2011
    More data:

    engine off, sender disconnected - lead = 7.5V
    engine off, sender connected - lead = 6.0V
    engine started and idling - lead = 5.6V (gauge reads 3 bar)
    rev engine and return to idle = 5.3V (gauge reads 4.5 bar)

    At idle the mechanical gauge always read 75. Revving brings it up some (only revved to 3k), but it always returned to 75.

    Are these expected Voltages at the sender? Perhaps Im not getting 12V to the gauge in the dash?

    thanks,
    Aaron
     
  13. airdelroy

    airdelroy Formula Junior

    May 10, 2007
    420
    Austin, TX
    Full Name:
    Aaron Richardson
    #13 airdelroy, Jul 31, 2011
    Ill do this next.

    Aaron
     
  14. fastradio

    fastradio F1 Rookie
    BANNED Professional Ferrari Technician

    Apr 26, 2006
    3,664
    New England
    Full Name:
    David Feinberg
    #14 fastradio, Jul 31, 2011
    Dealing with a similar problem now on a QV...
    Your sender voltages are typical and within the norm. Likely, you'll find that the problem lays with the oil pressure gauge.

    David
     
  15. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,507
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #15 Steve Magnusson, Jul 31, 2011
    Unfortunately, they don't give the schematic for the internal construction of the oil pressure gauge so requesting/getting a comparison voltage measurements (like David posted) are an alternative. You can easily check the upstream "supply" end for +12V being present (green wires at bottom of fuse #2), but that doesn't gaurentee that it's reaching the gauge in the dash.

    Do you have any other "weirdness"? Like with the engine running, if you turn on the headlights, do the gauge needles all shift alot?
     
  16. airdelroy

    airdelroy Formula Junior

    May 10, 2007
    420
    Austin, TX
    Full Name:
    Aaron Richardson
    #16 airdelroy, Jul 31, 2011
    340 ohms - engine off
    169 ohms - engine started
    142 ohms - engine revved and returned to 1800 rpms (high idle)

    Not really what RJay was saying it should be.

    Old sender reads 347 ohms.

    Aaron
     
  17. airdelroy

    airdelroy Formula Junior

    May 10, 2007
    420
    Austin, TX
    Full Name:
    Aaron Richardson
    #17 airdelroy, Jul 31, 2011
    The gauge do move to the right slightly when turning the headlights on. The oil pressure slightly more than the water temp/gas. The oil pressure might change a full bar in reading. However, I think it also did this when the gauge used to work.

    I get 12.5V at fuse 2 when the engine is off. Engine on I get 13.5V. Turning on the headlights drops it to 13.35V.

    thanks,
    Aaron
     
  18. Jeka

    Jeka Formula 3
    Silver Subscribed

    Nov 20, 2010
    1,181
    Rotterdam
    Full Name:
    Johan
    #18 Jeka, Jul 31, 2011
    I have had a similar problem with the electrical gauge. The indicated pressure was lower than the mechanical pressure. The problem was a wrong type of sender. My Mondial needed a 270 ohm sender where a 330 ohm sensor was installed. You can simply check if you have the correct sender. Just turn the key but don't start the engine. If you have the correct sender the gauge indicate "zero" else it indicates 1,5 bar (20 psi) high or low.

    The sender is a variable resistor where the resistance depends on the pressure. You can check the electrical gauge with some resistors. Disconnect the electrical leads from the sensor and connect in succession the following resistors:

    270 ohm type of sensor:
    270 ohm, gauge should read 0 bar or 0 psi
    180 ohm, gauge should read 3 bar or 43 psi (1/4 scale)
    100 ohm, gauge should read 6 bar or 85 psi (1/2 scale)
    10 ohm, gauge should read 12 bar or 170 psi (full scale)

    330 ohm type of sensor (i am not sure if these values are correct):
    330 ohm, gauge should read 0 bar or 0 psi
    220 ohm, gauge should read 3 bar or 43 psi (1/4 scale)
    120 ohm, gauge should read 6 bar or 85 psi (1/2 scale)
    10 ohm, gauge should read 12 bar or 170 psi (full scale)

    Your voltage readings (if measured at the sensor leads) are out of specs in my opinion:
    engine off, sender disconnected - lead = 7.5V (should be approx 12V - 13V!)
    engine off, sender connected - lead = 6.0V (should be approx 5.0V)
    engine started and idling - lead = 5.6V (gauge reads 3 bar), (should be approx 3,7V)
    rev engine and return to idle = 5.3V (gauge reads 4.5 bar), (should be approx 3.0V)

    You measured the following:
    340 ohms - engine off (You have a 330 ohm sensor!)
    169 ohms - engine started (This value represents a pressure of 4 bar or 60 psi)
    142 ohms - engine revved and returned to 1800 rpms (high idle), (This value represents a pressure of 5 bar or 75 psi!)

    It seems the sender is ok and the problem is in the gauge or the electrical connections. You are measuring 7.5V with a disconnected sender, it looks like the 12 V connection to the gauge is bad.
     

Share This Page