My 2005 4-cylinder 2.5s Nissan Altima has been having major issues for the past several months. My mechanic replaced the catalytic converter and a month later another mechanic said that the catalytic converter is completely disintegrated. Apparently the initial problem was with the ignition coils and that has been causing the problems with the catalytic converter. How are these two related?

  • Not sure, but I think it might be the shooting fire in exhaust. Might be caused by TPS sensor which shows more than it is at idle, which tells ECU to inject a tiny amount of fuel, which doesn't combust in a chamber, but combusts in exhaust. Most likely needs TPS adjustment or replacement. Only my opinion. Commented Jul 17, 2016 at 23:19
  • Could it be leaky exhaust valves through which combustion penetrates into the exhaust manifold and downstream into the cat converter? That could be tested with a cylinder leakdown test ?
    – amphibient
    Commented Jul 18, 2016 at 0:37
  • 1
    There's a whole lot of speculation going on here... The Altima 2.5s had some serious cat issues starting in 2003. The cat would disintegrate over time, and because it was so close to the exhaust valves the pieces would get sucked into the cylinders and cause significant engine damage. A failed ignition coil would send raw fuel to the cat, where it would ignite and disintegrate the cat. After that, given the design flaw, there's a good chance the disintegrated cat could've caused other damage. Commented Jul 18, 2016 at 3:50

1 Answer 1


Cats don't really like exposure to fuel. If your car has bad coils resulting in unburnt fuel, this can ruin a cat, hence how they are related.

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