P0420 2.7 l

Check your o2 sensors. Make sure you can force them lean by creating a vacuum leak and rich by adding an alternative fuel such as carb spray or propane to the leak. You should read almost 0v when you create the vacuum leak and just under a volt when you add fuel. Also check your fuel trims to make sure they are in control. If all that checks good, you need a new cat.

Low fuel pressure, as stated in previous posts, will not cause a P0420 code. It should cause a lean code, not a cat efficiency code.

I've fixed these codes many times and I've never been wrong if the o2 sensors are reading correctly and fuel trims are good.

 

I agreed with you until you said fuel pressure can't cause it. My experience shows otherwise.

 

MY 4 banger had your exact symptoms, pulled cat off and sure enough it was a bad cat.

 

Another thing you can look for if you can graph your o2 sensors on your scan is to look to see is the post cat

I read thru your post about your P0420 code. You had a seperate issue going on with surging issue. You are leading this guy down the wrong diagnostic path. If fuel trims are good, then the fuel pressure is good. If fuel pressure was low you would see positive fuel trims. If his fuel trims are fine he doesnt need to waste his time checking fuel pressure.

 

He can only read one fuel trim, short term I believe. Sounds like another problem.

 

It's his scan tool. He already said a different scan tool could read it.

 

"My short term and upstream sensor ain't reading. On other vehicles it does read."

 

It's the scanner. Not all scanners are created equal.

 

2.7L here with the same code. Ended up being my cat blew up from the inside out. Good luck and hope that's not what's wrong with yours. Mine was replaced under warranty.

 

Well that's what I'm hoping it's not either, because I know I could get new cats from rock auto for 200 but they aren't carb legal.

I haven't had time to check anything yet due to work, but only thing I know is that my urd simulator did help out tremendously tho.