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P0420 Code = Leaky Injector?

Augi

CEG'er
Joined
Dec 23, 2004
Messages
101
My car is throwing a P0420 CEL and idleing rough. I was told that the cat needs to be replaced since it's not burning the mixture right. I was also told by a guy who owns a '96 Monte Carlo that he had the same code and one of his injectors were leaking into the cylindar and it wasn't burning all of it off. He told me that if I were to change the plugs, one would be black from this bad mixture. and sure enough, when I changed my plugs the last time, cyl 2 plug was black and the rest were a greyish color. I know that all cars are differant, so I'm really wondering if anyone else had this trouble and what cured it.
 
the code difinitions for a monte carlo are most likely different then a contour ... P0420 on a for dis for the cat ...
 
OBD codes are standarized across the board except for a few manufacturer specific codes.

the P0420 could also indicate a faulty downstream O2 sensor. I would check the O2 sensor first, then test the injectors (if one of them is leaking it will most likely have a long crank time after sitting overnight), then the CAT. it may also be a combination of things. just remember that both injectors and O2 sensor will be cheaper than replacing the CAT.

are you getting any other codes or just the P0420?
 
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No other codes except that one. The car seems to like to die. Does anyone know if I can punch the cat until I get headers? or wilkl that ruin the way the car runs? I know it is clogging because it's starting to glow and the car is far from running lean. Has anyone tried this method?
 
You most likely have a misfire, not a faulty cat (originally). There is no indication given that your cat is clogged (yet), just that you're dumping excess fuel into it which will melt it in short order.

OBD-II codes up to P1000 have standardized definitions, all codes above P1001 are manufacturer-specific.

P0420 is extremely unlikely to be a downstream sensor. It may very well be due to the consequences of your continuing misfire.

Steve
 
p0420= catalytic converter efficiency low which really only means that your car won't pass emissions tests. my 96 zetec has set the same code for almost 20000 miles and runs just fine.
 
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