catalytic converter thermocouples | FerrariChat

catalytic converter thermocouples

Discussion in 'Boxers/TR/M' started by bpcurtis, May 10, 2015.

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  1. bpcurtis

    bpcurtis Karting

    Nov 5, 2003
    79
    Dickinson, TX
    Full Name:
    Burnell P Curtis
    My car is a 87 TR. The red light and buzzer came on saying that cylinders 1 - 6 were in trouble and I should slow down. Since the car was cold I know that the cat was not hot. The buzzer and light will eventually go off. The TCs plug into two modules located on the right rear fender. I reversed the thermocouple wire for 1 - 6 with 7 -12 and the same happened. I then switched the red plug with the green plug that come out of the modules and the light on the dash switched from 1-6 to 7-12. This proves to me that a)my cats are not hot, b)my TCs are not bad, and c) the module for 1-6 is bad. Anyone have any experience with these? Can I just unplug them with the red and green plugs?

    Thanks,

    Burnell Curtis
     
  2. 302Tim

    302Tim Formula 3

    Jul 2, 2011
    1,182
    Northern California
    Full Name:
    Tim
    The CAT ECMs are highly prone to failure. There were three designs over the life of the testarossa but even the last design was unreliable. Yes, you can just unplug them at the red & green connectors however, disabling them if you still have full (non-gutted) catalytic converters is not recommended as the converter matrix can break up over time and clog the air path, overheating and causing a fire. Replacements are costly. I just bought two used ones to replace one failed ECM on my car and neither used ECM works :(
     
  3. lear60man

    lear60man Formula 3

    May 29, 2004
    1,829
    Los Angeles
    Full Name:
    Christian
    Like Tim said, they are prone to fail. Mine are sitting in a box in the garage (one is dead one 50/50) Now you are in a catch 22; remove them and risk having a cat fire. Remove the cats and fail smog.

    Or check things periodically with a digital IR temp gauge (500F normal?). IMHO, cats dont fail over night. Poor performance, fuel smell, excessive heat are signs that your cats can be failing.
     
  4. bpcurtis

    bpcurtis Karting

    Nov 5, 2003
    79
    Dickinson, TX
    Full Name:
    Burnell P Curtis
    I will disconnect mine for the time being and check whether my cats are functioning or not. In the meantime, have either of you taken the module apart to see how it works? I bet it is an amplifier that boosts the voltage of the TC to something the computer can use. If one of you would want to, I would be glad to take one of the spare broken units apart and see if I can fix it. If so, I would send it back to you and repair mine.

    let me know.

    Burnell

    retired and bored.
     
  5. Cribbj

    Cribbj Formula 3

    #5 Cribbj, May 11, 2015
    Last edited by a moderator: Sep 7, 2017
    This system on the Boxers & TR's is probably similar to what we have on the later cars, (I have a 550) and yes, you're right, this "ECU" is simply a signal conditioner that boosts and linearises the millivolt thermocouple output up to a 0-5v output (actually more like 0.5 to 4.5) I've attached the output curve of a 550 unit below (generated from a thermocouple simulator box) and have noted where the 1st & 2nd alarm points occur (for the 550 ECU).

    It would be interesting to see the insides of one of your earlier boxes.
    Image Unavailable, Please Login
     
  6. lear60man

    lear60man Formula 3

    May 29, 2004
    1,829
    Los Angeles
    Full Name:
    Christian
    #6 lear60man, May 11, 2015
    Last edited: May 11, 2015
    John, I tore one up to look at the guts...I'm sure it's fairly simple to an electronic guy. I think we spoke about an aftermarket solution before that is available for other facts.

    I'm on my iPhone so I can't post a direct link but..... If you search the TR section of Fchat for 'CAT ECU'......I started a thread on 1/1/2013. I posted pics of what it looks like inside and the conversation with cribbj. But the graph above confirms my previous estimate of what temp a healthy cat should run at (500).
     
  7. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
    33,736
    Austin TX
    Full Name:
    Brian Crall
    I have seen 2 references to cats causing overheating. Cats do not cause overheating, the running condition of the engine does.
     
  8. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    12,661
    San Carlos, CA
    Full Name:
    Mitchell Le
    The electronic is simple, but it is all encased inside module that tends to destroy itself after the casing material is removed.

    An thermocouple needs a high gain amplifier, and a reference to a room temperature. The analog amp, subtracts the reference signal from the TC signal and gains it up by 100 or more. The amp is normally an opamp, running between Grd, and 12V.

    The failure mode is normally not the electronics but the solder points, connectors, etc. that go first.
     
  9. Cribbj

    Cribbj Formula 3

    Christian, I found your thread, but didn't see any pics of the guts? Only the outside case and connectors. If you have pics of the guts please post 'em.
     
  10. lear60man

    lear60man Formula 3

    May 29, 2004
    1,829
    Los Angeles
    Full Name:
    Christian
  11. ozziindaus

    ozziindaus F1 Veteran
    Silver Subscribed

    Aug 16, 2012
    9,799
    Detroit
    Full Name:
    Sam
    Happened to me too. It turned out to be a bad ground.

    Does this happen sporadically?
    Does it start ON but then become intermittent and finally turns off?

    If so, then I'm sure it's a bad ground.

    Try this. With the engine running cold and the CAT ECU unbolted but with all the connections in place, the buzzer and light should turn off. When you run the bolts thru, you'll notice a tiny spark and the buzzer and light will come back on. I isolated the bolt and all good.

    Note that I am possibly just masking the real issue by un-grounding it so please take this advice with caution.
     
  12. Cribbj

    Cribbj Formula 3

  13. lear60man

    lear60man Formula 3

    May 29, 2004
    1,829
    Los Angeles
    Full Name:
    Christian
    #13 lear60man, May 12, 2015
    Last edited: May 12, 2015
    Trunc...what? Internet is limited on my plane......a little better than dial up but not like at home. I dug out the direct links to my photobucket account.


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