i have had a miss at idle for sometime now, and i scanned it with a live scan genisis. the car has been tripping a code for a while, the dreaded p0420 cat code. i was told this wouldnt cause a miss. but when i scanned it it was showing misfires happening at idle, but never once actually threw a misfire code. i did the usual plugs and wires and routine stuff, and havent fixed it yet. any ideas? i am hoping its not internal. car has 41k on it, it a 02 ls1. any help is appreciated guys.

scan also said spark was between 16 and 20 degrees at idle with an a/f of 14.3

 

I think the cat can cause the miss fire,the cat sensors decides what to do as far as engine paremeters, A/F ratio, timming etc... either sensor is bad or cat. it's cheaper to change cat sensor then cat ... .02

 

there is a sensor on the cat? btw i took the car out today, and if you hit it full throttle, from a dead stop, the car completly bogs down and doesnt get going for about five seconds. does anyone know exactly what the po420 cat code makes the motor do different? i am about ready to trade this car in i am sooo frustrated.

 

No their is no sensor in the cat, he is referring to the front 02. P0420 is just letting you know that the cats aren't working either because you removed them/they are clogged/ or your rear 02's are shot.

A miss at idle can come from bad plugs, bad wires, or a faulty coil just to name a few.
Replace the plugs and make sure you get all the wires on there nice and tight.

 

will the car run different with that p0420 code active? because it just seems like it is running rich. so could i just have all the cat related stuff tuned out and be done with that? i was gonna put longtubes on next week

 

No the car won't run any different with the code, you can have the Code and CEL turned off when the car is tuned.

 

what if the cat itself is shot, or clogged, would that make it run different? i am going to compression test it tommorro just to rule it out for peace of mind. what do you guys think the compression should be at for and ls1?

 

If the cat is clogged that is a different story. The car will not be able to have its flowing exhaust like it likes. I have seen them make manifolds glow red at night because of this on a silverado (it was pretty cool and I'm glad that pos wasn't mine).

 

i did notice that it has been unusaully warm and takes a while to cool off after i stop running the car.