P0420 OBD-II Trouble Code..great

[BrApple]

Here's my question: If there's an issue with exhaust flow through the precat, and you simply install a mil-eliminator, how is that a thorough solution? Seems to me it's the precat that should be getting the attention.

If there are no issues with performance, could there really be a problem with the precat itself? Changing out the downstream O2 sensors won't solve the problem, I take it?

have to remember that the original pcm programming had the limits set to tight ... you would get a pre-cat code (p0420 or p0430) when it wasn't real. I had them on my car but I really don't think that the pre-cats where shot nor plugged. Ford did reprogram a number of cars to correct the CEL from turning on when it shouldn't.

so the mil-eliminator is there to turn the cel off.

 

[Dan the rug man]

P0420

P0420

Per tech service bulletin # TSB 01-9-7 RE: Catalyst efficeiency Trouble codes P0420 & P0430. Possible causes 1) Malfunctioning Engine Coolant Temp sensor 2) High fuel pressure 3) Damaged Exhaust manifold 4) Cylinder misfiring 5) O2 sensor wiring concerns (shorted, chafed, bent pins ect 6) Damaged exhaust system pipe 7) damaged muffler / tailpipe assembly 8) retarded spark timing.
With these being the list of items ford mechanics would look at, would that make sense for us to look at the same possible causes? If your O2 sensor is old it may make sense to change the sensors. You may be putting MIL Eliminators on O2 sensors that have no issues. ECT sensor is like 20 bucks and takes 15-30 minutes to change. Start there and work your way down the list like a Ford trained mechanic would. Dan

 

[projectSHO89]

Certain of those causes will cause an over-rich exhaust mixture that, if left unrepaired, will quickly and (usually) permanently damage the catalyst in the pre-cat/exhaust manifold. It becomes saturated with fuel and can no longer fire off. The B-12 treatment can clean this up and sometimes restore catalyst performance. A MIL-eliminator can mimic a downstream sensor that is reporting proper catalyst function

Pre-cat failure will only affect perceived performance if the structure melts or brakes and obstructs exhaust flow. If the substrate has failed mechanically, a MIL eliminator will not be of any help.

Personally, I've yet to see a downstream sensor itself cause a cat efficiency code.

Steve