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O2 sensors showing zero volts...

Discussion in '348/355' started by cactussed, Nov 24, 2021.

  1. cactussed

    cactussed Karting

    Mar 12, 2008
    172
    Hi guys

    Chasing an issue on my 97 355.
    I just changed one of my pre-cat O2 sensors to a walker one and now all my O2 meters / lamdas are all showing zero volts.
    I've checked the 10A fuse and its fine. Kinda stumped as to why they might all suddenly be offline?

    Any ideas please?
     
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  3. Qavion

    Qavion F1 Veteran
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    Feb 20, 2015
    6,265
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    Ian Riddell
    Is your car 2.7 or 5.2.
    I haven’t heard of anyone using a Walker O2 sensor on a 5.2 car. The 2.7 and 5.2 OEM sensors have different part numbers. I’m not sure if they are interchangeable.

    Did you buy them with pre installed connectors or did you have to fit them yourself?
     
  4. 26street

    26street Karting

    Jan 30, 2021
    126
    Westchester New York
    Full Name:
    Mark k
    Walker only shows one part number for all models from 95-97 f355
    Bosch shows 2 numbers the spider and gts was the same and the Berlinetta is different
    Most searchers don’t even show the Berlinetta as a option??????


    Sent from my iPhone using FerrariChat.com mobile app
     
  5. yelcab

    yelcab F1 World Champ
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    Nov 29, 2001
    11,051
    San Carlos, CA
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    Mitchell Le
    What does it do if you put the old sensor back?
     
  6. Qavion

    Qavion F1 Veteran
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    Feb 20, 2015
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    Strange... online searches come up with these (pre-cat) equivalents..
    2.7 P/N = 158730 (1994~1996) = Bosch 0258003309
    5.2 P/N = 169953 (1996~1999) = Bosch 0258003819

    ... but the vehicle range for these Bosch numbers stretches across all years of 355 manufacture.

    The earlier car Bosch O2 sensors seem to be much cheaper (Ferrari OEM about the same)

    https://www.ebay.co.uk/itm/144141180408?

    I'm guessing they are not equivalent, but you would think they would put out some voltage.
     
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  8. cactussed

    cactussed Karting

    Mar 12, 2008
    172
    I purchased from superfrmance. It’s a 5.2 car and it’s bank 2 pre-cat sensor, so
    I’m hoping they know what they’re doing.

    is there a relay which covers all the sensors? Seems odd that all of them are suddenly showing zero voltage
     
  9. Qavion

    Qavion F1 Veteran
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    Feb 20, 2015
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    Ian Riddell
    Do you mean the heater volts or the sensor volts? The power for the sensor element comes from the ECU. The power for all the O2 heaters comes from the fuse (22) and relay N (fuel pump relay). The car wouldn't start if the relay was faulty.

    You need the engine turning before you get heat power for the O2 sensors.
     
  10. cactussed

    cactussed Karting

    Mar 12, 2008
    172
    right. Sensors are now showing voltage but I have no fuel trim values, which I think is causing the rough idle. Any idea what drives those?
     
  11. yelcab

    yelcab F1 World Champ
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    Nov 29, 2001
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    Mitchell Le
    How about you shut your car off, cut the battery power, wait for it to cool off, and reconnect the battery and fire it up, let it idle for 10 minutes til warm up before you try to read anymore values.
     
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  13. Qavion

    Qavion F1 Veteran
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    Ian Riddell
    Maybe you could fill in a few of the gaps.

    Why did you change only the left bank pre-cat O2 sensor? Because of the rough idle alone? Or because your scanner also produced an O2 sensor fault codes? Did the rough idle suddenly happen (after a an extended period of not driving)? What are the codes?

    When you say your sensor are now "showing" voltage, do you mean the car is now supplying heater voltage to the sensors or do you mean the sensors are outputting voltage to the ECU? Or do you mean both?

    How are you measuring the voltage? (backprobing the O2 sensor pins ?)
    Can you back probe the grey and black wires to see if there is a voltage across them?

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    I think there is still some uncertainties regarding what happens after a battery reset on a 5.2 car, but it can't hurt (if you have recorded the stored faults).

    https://www.ferrarichat.com/forum/posts/147610748/
     
  14. cactussed

    cactussed Karting

    Mar 12, 2008
    172
    Thank you to everyone who's been so helpful.
    Background - I've been chasing a problem on the car on and off for some time now. It ended up being several things but the major item was I'd been sold a car with a cracked block which the independent I purchased from had tried to fix with chemical metal (complete with thumb prints). In his defence, it lasted a good many years but finally cracked, seeping coolant into the block and requiring some work.
    Car has now just come back from a build (replacement block, liners, new rings, bearings, oil pump rebuild, new valves, valve guides etc), Essentailly everything bar the pistons and conrods is either new or rebuilt, Don't ask how much. It'll last the length of my ownership over the rest of my lifetime.

    Picked the car up and drove it back (still running it in so under 3k rpm) and to my ear it didn't sound quite right (but drove OK so I drove it home). Curiosity got the better of me, so I plugged my iPhone OBD2 reader in and it showed no short term fuel trim on bank 2, (vs a reading on all other sensors) so I figured I had a dud sensor prob from the coolant being burnt just prior to rebuild). For reference, Bank 1 short term fuel trim = -3.13%, long term = -3.91%, O2 sensor 1 Bank 2 short term trim 0%, long term trim -5.47%.

    So, changed Bank 2 sensor 1 (nearest the headers, blue ribbon wire) with a new sensor from superformance. Getting old o2 sensors out is a rubbish job.

    weird sounds still persists.
    I've also checked impedance on all plug wires and they seem good, And changed coil packs just in case, but no change. plugs are all brand new. Fuses all seem fine as well.
    It sounds electrical to my ear but am a bit stumped,.. now wondering if it m ay actually be a manifold blow.
     
  15. yelcab

    yelcab F1 World Champ
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    Nov 29, 2001
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    Mitchell Le
    The last complaint of "it sounded weird" on a 355 turned out to be bad header. That was last month, and the fix was new Tubi headers.

    I suggest:
    Smoke test the exhaust
    check bypass valve operation
    Check for tightness of all exhaust gaskets and fasteners
    Check intake leaks

    Your long and short term fuel trim look OK for now. With that much engine problem and that big repair, you should have changed all O2 sensors and start fresh.

    Until there are more clues, that is all to do.
     
  16. 26street

    26street Karting

    Jan 30, 2021
    126
    Westchester New York
    Full Name:
    Mark k
    Ok so I think I understand what’s going on
    You pick up the car after a rebuild of the engine and it ran fine and just didn’t sound right too you so you put a iPhone obd2 reader on it and had fuel trim reads on back 1 short term -3% and long term -3.5 % “good so far” and bank 2 short term 0% and long term of -5% “still ok”
    These readings on a fresh engine rebuild are ok —- the ECM is taking fuel away and running lean which is good you are not pushing the car over 3k rpm which is the right thing to do for the break in

    So at this point maybe putting some more miles on and see how it goes there is to many new parts and probably old fuel “lol” and stuff that needs to be ran through so unless you hear bad noises or engine starts missing running rough etc just run it and enjoy
    Sounds like the car had a little bit of a hard life before but you are doing the right thing now by straighten out all this problems


    Sent from my iPhone using FerrariChat.com mobile app
     
  17. Qavion

    Qavion F1 Veteran
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    Feb 20, 2015
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    Just curious... Does your iPhone OBD2 reader allow a graphic representation of the O2 readings (against time)?
     
  18. cactussed

    cactussed Karting

    Mar 12, 2008
    172
    Minor update. Spent the whole day in the shop yesterday with the engine builders.
    - my original o2 sensors was indeed dead.
    - the replacement from superformance oddly caused all 4 sensors to read zero, but when unplugged the remaining 3 came back to life.
    - with a different sensor installed, all 4 now work but the car still sounds like its missing slightly. Like its running on 7.5 cylinders.

    No error codes showing.
    Hydrocarbons out both sides (and other gases) all look OK.
    Disconnecting injectors makes a difference so they appear to be working (and they've all been rebuilt and flow tested).
    Coil packs and leads are also working fine.
    No5 plug looks a bit brown (all the others look perfect). Tried swapping plugs but no change there either.
    Put a smoke machine on it and zero visible leaks.

    Its a mystery.
     
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  19. Qavion

    Qavion F1 Veteran
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    Feb 20, 2015
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    Ian Riddell
    I think I'll be taking Walker O2 sensors off my shopping list (at least for 5.2 cars)

    Thanks for the update.
     

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