Periodic Codes: P0420, P0193

rgorke

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First, Happy 4th of July weekend!

Second, '04 V8 with 267,000 miles. I've got 1500 miles on my refixed transmission and the vehicle is running great, except for...

Third, car throws a P0420 code (catalyst below threshold Bank 1) every month or two. I also got a P0193 (High fuel pressure) a couple weeks back. The P0193 code only pops up when I go down a long 2 mile 7-8% grade after a slight incline on the freeway. If I monitor the fuel pressure while driving, it usually sits at 55 +/- 3.

I understand that the P0420 code could be the Cat or O2 sensor (upstream?). What are my options for further diagnosis? Switch O2 sensors between banks to see if issue follows sensor? That would determine if the issue is the O2 sensor or the cat, right?

Finally, what size is the O2 sensor tool, 303-476?
 
Usual O2 sensor wrench size is 7/8". Most of my experiences with P0420 are usually correct in calling out a failing cat. I have successfully utilized adapters to pull the sensor tip away from the exhaust stream to sample less of the unburnt fuel passing through the cat. I got 3-4 years extension out of the last one I used on a subaru.
 
The P0193 code only pops up when I go down a long 2 mile 7-8% grade after a slight incline on the freeway. If I monitor the fuel pressure while driving, it usually sits at 55 +/- 3.

IIRC... on a downgrade the LS will shut off the injectors to save fuel... until the throttle is depressed again.

This could cause a short "spike" in pressure. I think it should drop. If it stays high... I don't know if that's normal or not.
 
Usual O2 sensor wrench size is 7/8". Most of my experiences with P0420 are usually correct in calling out a failing cat. I have successfully utilized adapters to pull the sensor tip away from the exhaust stream to sample less of the unburnt fuel passing through the cat. I got 3-4 years extension out of the last one I used on a subaru.
Mikey, what did you use for adapters for this? Did you just use washers? How far out to you need to move the sensor for this to work? I am getting a P0430 code right now and would like to try this.

Nevermind, I found them. Interesting idea that I am going to try.
 
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