Continued P0420

re: P0420 Addendum to my post of 30 Jun '22:

As of Mar '23. First, thanks to everyone who replied to the original post. I should explain that the O2 sensors or probably 3-4 yrs old (Bosch--I didn't know that Denso is the preferred), and last year I had the cc out and was able to see right through it. Since the original post, needing a new muffler and unable to get the Walker parts, I had the exhaust system fabricated at a local shop from back of the cc on. It's pretty tight.

It seems like that front cc flange connection keeps coming loose. I replaced the larger flat gasket with the "donut" type, which fits in a recess in the cc opening. I used just a dab of (semi) hi-temp rtv (500°) to hold it in place. I still used the locking nuts. It held for a couple of weeks and then--you all know the story. The performance begins to degrade, getting worse and worse, fuel consumption goes up, and eventually the light comes on. The code check reveals everybody's favorite lottery number (Hey, maybe ...!)

With regards to a possible leaky exhaust manifold gasket, I asked a shop about pressure testing the system, which couldn't be done anyway until the flange connection was tightened. They suggested that the thing to do would be do have the connection welded. It's not my first choice, for obvious reasons.

I'm sure that fellow posse are familiar with this experience. Can anyone who's successfully dealt with this problem share what they've found and done?

Thanks in advance

niq98

Last edited: 1 minute ago

 

Not sure if it was a general auto repair shop or not but might consider taking it into an exhaust only shop and have them look at it. Ask them for options re: the flange. Use a different shop than the one who did the rear exhaust work.

 

Thanks, Area 51. Other issues have preempted my attention and energies right now. In the meantime, have had to ignore the indicator light , which I hate doing. It seems that the performance has sort of returned to almost normal, though, as far as response and mileage. It's like the leak is marginal, just enough to trigger the code. But no self-respecting, technically involved driver can live long with an ugly checkp-engine light in his face, so I'll get to it and figures it out.soon.

 

I had a pinched wire on o2 sensor causing a issue on mine

 

I'd like to thank everyone who replied with suggestions to my post.

Here's what happened, and I think I've got it licked. A lot of the problem was that the parts wtores were selling me the wrong gasket. It turns out that there are two gaskets that show up on their computer, one that fits the inset in the cc side of the flange connection (smaller), and one that fits the engine pipe (larger). The larger one is the correct one, as it extends out close to the flange bolts, so that they close better mechanically. the small one just caused you to deform the flanges as you tighten the bolts.

I also applied a generous glop of gigh-temp RTV (the Copper was recommended to me), and followed their instructions. It seems to have worked. The dreaded "check engine" light hasn't come on for a couple of weeks now , and I hope it stays that way. Oh, make sure the RTV package explicitly says, "sensor safe", or you'll end up doing it twice and having to replace the upstream O2 sensor as well.

I hope this helps someone out there.

PS: This is why I so lament the disappearance of the local, owner-owned parts shop. where you'd have the owner and decades of experience behind the counter.; people who knew what tjey were doing, instead of a body hired for 20 hours a week who doesn't know the difference between a steering and a flywheel. Oh, well, just had to get that in.

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