Help diagnosing P0420

Hi everybody, this is my first post, so apologies if a thread like this already exists, but I’ve obviously been looking around and haven’t found anything helpful.

I drive a 97 4wd 2.7L manual transmission, and about a month ago it started driving a lot more rough. Soon after, a P0420 code popped up - catalyst system efficiency below threshold. The suggested fix is a new cat, but I’m in Colorado and have to buy one that passes all the emissions and everything.

symptoms I’m experiencing are heavier ticking, loss of power, and what I would call lurching whenever I get off the gas without the clutch depressed. After I press on the accelerator, the truck doesn’t seem responsive and it takes a quick second to get going.

I tried new O2 sensors, new air filter, going to replace plugs and wires this weekend and potentially remove the cat and clean it with vinegar or something. Fuel pump was changed less than a year ago, and it doesn’t seem like the same symptoms.

Appreciate the help in advance.

Thanks,

 

Welcome to TacomaWorld
Exhaust leaks upstream of 1st sensor can throw P0420. Loud ticking makes me think cracked exhaust manifold.
Forget washing the Cat but you could try Cataclean, it's a temp fix at best.

 

My P0420 code was a leaking exhaust. It was missing a flange gasket and a bolt. That was repaired and code has been gone for 2 months now. I'm not sure of that would cause your other issues.

 

I second this, if it's a stock 97 you've got a cast exhaust manifold and those are prone to cracking, which can cause that code to come up.

A cracked exhaust manifold was the cause of my P0420 in a 98 4R that had the 2.7

 

I have the same code/problem. Cracked manifold. Second time

 

Ok that’s good to hear that everyone is thinking the same thing. I always try to do my own work on my cars, but haven’t done much exhaust work. Any tips on how I can find/confirm that’s the issue?

 

Upgrade to the 01+ welded manifold.
That's what took care of my constant cracking exhaust and eventually took care of my P0420

 

Visually inspect the manifold itself. 2 of the 3 2.7motors I've had, have had visible cracks on the manifold itself by just getting my face close and looking.


Sometimes it's on the underside of the manifold. The absolute best case to check the issue is remove the manifold itself and seriously look at it.

 

I fought this code for months on my truck. My advice is start with the basics and work your way up to the expensive stuff. This code can get expensive if you just toss parts at your truck.

Many things can cause P0420 code. Everything from a dirty throttle body to a burnt valve. Properly diagnosing will save money in the long run.

Mine unfortunately was a bad first cat. It was broken up and making and ticking and rattling noise as well. Unfortunately it blew into the second cat and clogged that one as well. Luckily I am able to use the eBay cats where I live.

 

When I had this code I cleaned my throttle body, and MAF sensor and it went away. My K&N always let oil all over the MAF so it would pop up frequently until I switched filters.

 

What’s the best way to clean those?

 

Is there a certain brand of exhaust manifold to look for assuming that’s the issue?

 

For the MAF just some electronics cleaner spray from local autocrats store, its super sensitive so don't try to scrub or brush it with anything just spray it a few times and let it dry. Throttle body I removed and hit with brake cleaner.

 

UPDATE: Today I changed the plugs and wires, while I was doing that, I took off the heat shield for the exhaust manifold expecting to see a big crack and I observed nothing out of the ordinary.


I also thoroughly cleaned the throttle body and MAF sensor, and there was also no change in the sound of the engine and the smell.


While I was putting everything back together I decided to listen near the manifold and I noticed a pulsing blast of air coming from this hole:

is this where the issue is coming from? This little hole? Does the heat shield mounting bolt really plug a hole in the exhaust manifold? Seems silly, but it’s my last thought.

Would really appreciate some more feedback. Thanks,

 

I put Seafoam in my intake through the brake booster and the white smoke was coming out of my manifold. That how I found it

 

No crack, no loud exhaust when cold, no other codes. It's the cat then.

I have no idea why people throw o2 sensors at p0420, I wish they would stop suggesting it on pages.

 

Idle the truck and check around all the exhaust flanges with your hands, if you feel any puffs then it's the gaskets. Easy fix. Don't rely on sound alone, you need to feel if there are any leaks.

 

Yea that picture circled in red in my last post had puffs of air coming out of that bolt hole. Is it possible that the bolt to hold on the heat shield would seal the manifold? That doesn’t make sense to me.

 

The cracks can be very hard to see. My apologies if you already checked but make sure you check the exhaust flanges. They commonly leak and are a cheap fix.

Op also realize the code could be a combination of things, especially since you mentioned it has drivability issues. Leaking exhaust flange, cracked manifold, and very likely you will have to fix the cats anyways.

I’d pull the cats off if they aren’t to rusty. Look inside and see their condition. If you can’t easily see light or chunks are falling out then you know you should start from there.

I’m sure you’ve already done it but read the other 100 threads about this code.

 

Also in order to properly clean the throttle body it really has to be removed. Removing the TB also ensures all the crud just doesn’t sink to the bottom of it and wreak havoc. The opposite end of that butterfly valve is probably still caked in crud.