355 Cats (Temps) | FerrariChat
Buy

355 Cats (Temps)

Discussion in '348/355' started by DT-355, May 17, 2008.

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

  1. DT-355

    DT-355 Karting

    Oct 14, 2007
    51
    #1 DT-355, May 17, 2008
    The cats on my 1995 - 355 are running at different temps. The 1-4 side is always 100 Degrees or so cooler than the 5-8 side. Is this normal? The car runs fine, but I get a little crazy when I find something that doesn't make sense to a layman like myself. The 5-8 runs about 330-360 and the 1-4 side is around 230-240. The fans are working fine, but I’m just concerned. Anyone have an answer? Thanks Guys.
     
  2. Marco Bussadori

    Marco Bussadori Formula Junior

    Aug 6, 2007
    430
    London
    Full Name:
    Marco Bussadori
    #2 Marco Bussadori, May 19, 2008
    Cat heats up proportionally to the unburned fuel it gets from the cylinders upstream. The excess fuel burns in the cat and it heats up. Three ways you have different heat:
    1) Air to fuel ratio differs between banks - this i usually set by the Oxygen sensor telling the ECU if the mixture is set properly
    2) One cat flows better than the other - more air moves through, more heat is carried away - maybe the hotter cat is clogged more than the cooler one, maybe your air injection is stuck open on the cooler cat...
    3) One cat is newer than the other - usually newer cats will flow better than older ones

    O2 sensor differences are not great - too lean a mixture, means there is less unburned fuel to carry heat away (yes, this is true, in Aviation you actually can cool the top cylinders by running the mixture slightly rich) and lead to premature valve/head failures.

    Clogged ECU's are not good too for performance reasons. Your cats have ECU's which shut the bank down if the temperature is way too high.

    Real basic question, you're sure you are mesuring the cat surface on both right, eg. measuring cat surface on one and the heat shield surface on the other WILL give you about 100 degree difference if not more...

    Marco
     
  3. DT-355

    DT-355 Karting

    Oct 14, 2007
    51
    #3 DT-355, May 19, 2008
    Thanks Marco, so far you're the only one that's responded. I just replaced the ECU's, but not the Oxygen sensors. The 1-4 was shutting down and it fixed the problem. The temp was different long before the ECU failed, but I'm worried about more problems down the road. The 1-4 Cat is the cooler one running about 230 or so, the 5-8 is running 330 or so. I think I'm checking the temps. the same way on both sides. I'd like to know what's the normal temp. for a 1995. What's toooooo hot and if the diff. matters. I'm going to call a dealer later today, but I'm so far from a Tech. it's hard to just take it in.

    Marco, thanks for your help. Dominic
     
  4. jssans

    jssans Formula Junior

    Jun 1, 2005
    839
    St. Louis
    Full Name:
    Josh
    #4 jssans, May 19, 2008
    I have a '95 F355 & my CAT temps were 100 degree different as well. That is why the passenger side exhaust manifold always goes bad 1st, IMO. I got rid of the CATs things are much better. Manifolds are much healthier & I never have to worry about CAT failure, EVER!
     
  5. 348SStb

    348SStb F1 Rookie
    Owner

    Apr 9, 2004
    2,991
    Palm Beach County, FL or Nassau County, NY
    Full Name:
    Dave
    #5 348SStb, May 19, 2008
    Hi Dominic,

    I would highly recommend doing a 4-gas analysis on your car. You must test the gases both BEFORE the cats and AFTER the cats. A well-versed Ferrari technician will be able to tell you about where the numbers should be.

    The car should run properly on its own -- i.e., without the cats. If the analysis of the gases before the cats shows numbers that are off, you will know that your problem is not with the cats, the cat ECUs, or the oxygen sensors. The oxygen sensors serve only to make minor adjustments in the fuel mixture -- they are not supposed to correct an underlying problem that shouldn't exist in the first place.

    If the numbers before the cats are normal and the numbers after the cats are whacky, then you know that your problem is either with the oxygen sensors, the ECUs, or the cats themselves.

    I would highly recommend this procedure in conjunction with purchasing new catalytic converters if you are using the original cats.
     

Share This Page