P0420 Code after DOD Release

[OklabyGodhoma]

To answer as much as possible. The cam is a stock replacement because of the original having gaulding because of a stuck lifter. The kit was just over $900 because I wanted to replace all bolts gaskets, VLOM, an yes I had other work done at the same time. Had the rear end rebuilt because of a carrier bearing starting to make noise and also has front bearings and new brake disc drilled and grooved and ceramic pads. My OBDII keeps throwing the code so it looks like I'll start with the upstream O2 sensor and go from there. It just seems strange that this happened after all the work was done and never once had the code before then. Total labor cost was $3858 including a couple of parts like motor mount on right side.

I have no way of knowing the programming done on the computer. It was supposed to be to eliminate the signal to go from 8 to 4 cylinders and back and just stay on 8 but otherwise I do not know. I know lots have done the DOD release so I was hoping that someone had come across this before.

Needed to add that the computer was programmed several months before the full release work was done. I had torn it down from the top so I could get to the lifters under the VLOM and did a manual lifter release for a stuck lifter. That worked for a few months and then the lifter stuck again. That's when I decided to have the full meal deal done. I'm 73 and after 3 back surgeries the thought of bending over that engine to do the work again just turned my stomach so I bit the bullet and paid all the labor cost but supplied the parts I wanted installed. The rear end and front work parts were all Detroit Axel so I know all the parts for the work were of high quality.

 

[swathdiver]

I recently did a full DOD release using a kit from Texas Speed. New cam, new VLOM plate everything new. Had the computer flashed by the guy that CPR recommended. A week after the car starts throwing a P0420 code. Tried using Berryman’s as well as a gallon of Lacquer Thinner with 10 gal of fuel. Still throwing the code. Almost forgot also new exhaust manifold gaskets.

Looking for ideas or if anyone faced this problem after a DOD release. I’ve got almost $4K in this engine now and it’s pissing me off…..HELP!!!

If all the sensor readings are normal now, it may have been related to problems before hand. It is well known that a failing AFM system takes out cats.

Save for a massive exhaust leak, a P0420 means just that, a bad cat. Don't skimp and use cheap ones either, they don't last at all. Get a good quality Y-pipe with 2 or 3 new cats and move on. I used Magnaflow for mine.

Darn, those stock replacement camshafts cost you about 10 horsepower, they are LM7 grinds and not L33 which is the same as your original without AFM.

Norman, Oklahoma eh? I flew my girls out there in September to bring back a 2013 Sierra we bought from Ferguson GMC.

 

[OklabyGodhoma]

OK so what am I looking at for a new Magnaflow? Geez, this Yukon has almost 140K so it's not abused but it's costing almost too much.

 

[swathdiver]

OK so what am I looking at for a new Magnaflow? Geez, this Yukon has almost 140K so it's not abused but it's costing almost too much.

I'm not up to date on the latest prices, did mine 5 years ago. Probably around a thousand dollars these days. Yeah, you've spent a bundle but it pales in comparison to a new one. Once done it will give many years of good service. But in about 20-30K miles you may have to overhaul your suspension. Did mine at 162K.

 

[Geotrash]

OK so what am I looking at for a new Magnaflow? Geez, this Yukon has almost 140K so it's not abused but it's costing almost too much.

Yes, this is the mid-life crisis for these trucks that you're experiencing. But once you're through it, you can figure another ao years and 150K miles of reliable operation if you keep up on the maintenance.