slow down light w/ no cats???????

Discussion in 'Technical Q&A' started by ENZOFORZA, Sep 13, 2004.


    ENZOFORZA Karting

    Nov 3, 2003
    Full Name:
    I have a '95 355 with cat bypass/tubi installed. Car has run like a top until recently. On a long trip back from Foxwoods to Boston, car all of a sudden throws a Check engine light and loses power. The exaust changed its note and sounded sick. after a few miles check engine light stays on but sick exaust nose goes away and power returns to normal. its a problem that comes and goes frequently. car runs fine about 95% time and sounds sick + down on power the other 5%. The other thing is that the slow down light comes on but I do not have any cats??? the only thing I can think of is the addition of BMC filters about 1 month ago. The car ran fine for the first 2 weeks with them installed.

    ENZOFORZA Karting

    Nov 3, 2003
    Full Name:
  3. MS250

    MS250 Two Time F1 World Champ
    Lifetime Rossa

    Dec 10, 2003
    Full Name:
    On my TR when I went Borla with no cats, the car had a similar problem. It had to be balanced correctly. Apparently, since the air flowed better it threw off the system and caused all kinds of idling problems, plus the slow down light. My mechanic fixed it,he just had to get the fuel / air mixture accurate in all 12 banks. 1 of the banks was throwing off the whole thing.
  4. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    Full Name:
    Steve Magnusson
    Jake -- If the same slowdown light always comes "on" when you have the problem (of one bank shutting down) then almost certainly the slowdown warning light ECU (a.k.a., thermocouple control unit) for that bank is flaky. One thing to try is swapping the two warning light ECUs and seeing if the "problem" moves to the other bank (i.e., if the other slowdown warning light now comes "on" when you have the problem) -- this will also give you a chance to just make sure that all the warning light ECU connections are relatively clean/healthy/reseated. As you noted, without cats it's virtually impossible for the exhaust to really overheat so any slowdown warning light must be a false indication.

    Another indicator that a warning light ECU is flaky is if your self-test is not always working well -- is it?
  5. scotsman

    scotsman Rookie

    Apr 10, 2004
    Portland, Or.
    Had the same problem, most likely it is one of the two thermocouple control units.
  6. 355Aloha

    355Aloha Karting

    Feb 15, 2004
    Honolulu Hawaii
    Full Name:
    John N
    I have the same problem for several months now. It come and goes. I get code 1445 and I can reset it with a OBDII code unit.
    I am tring to find out if a way exist to test if it is one of the two ECUs or thenmal couple with out taking it back to the dealer again.
  7. Ken

    Ken F1 World Champ

    Oct 19, 2001
    Arlington Heights IL
    Full Name:
    Loss of power at higher RPMs frequently is critters/blockage in the exhaust.


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