P 0420 code

I Bleed Ford Blue · Apr 3, 2018

For those of you that have long tube headers on your S 550, did you get a cat inefficiency code and did it appear right away after header install. I installed a set of long tubes on mine back in Feb and all was fine until today. I got a P 0420 code for cat inefficiency after putting approx 120 miles on the car since install.

Boone · Apr 4, 2018

Are you running off-road connector pipes?

I Bleed Ford Blue · Apr 4, 2018

No, I have cats installed.

Boone · Apr 4, 2018

If you're running green cats I don't understand why it threw a light. If your running what is commonly referred to as "high flow" or "race cats" it could be a couple of things. The first thing I would try would be 02 sensor spacers, search Amazon for Universal O2 Sensor Spacer Adapter Isolator m18. These will pull the sensors back some and essentially desensitize the 02 sensor. They work on our S197 car. I have read a lot of your posts and if I'm right, I don't think you run your car really hard. Sometimes the guts in those small cats overheat and clog up the exhaust, but that's mostly on boosted cars running high horsepower. If it were me, I would clear the code and run the spacers and that will probably eliminate the problem. If it doesn't, your only out a few bucks.

Boone · Apr 5, 2018

After studying this a little there may be more to it. Check out this link.... https://www.engine-codes.com/p0420_ford.html

I Bleed Ford Blue · Apr 5, 2018

I actually have the cats that came with the headers, which I believe are high flows. What concerns me is that its only bank 1, not bank 2 also. I'm thinking I had a O2 sensor go bad or come unplugged.

Boone · Apr 5, 2018

That's entirely possible. Maybe something as simple as a connector didn't snap all the way into the socket. The videos I watched opened up a few possibilities.

I Bleed Ford Blue · Apr 6, 2018

I took a peek under the car and I have to replace the band clamps aft of the x-pipe. Apparently they are one time use because now my exhaust is hanging down and leaking at the joint. Just to be clear, the factory exhaust pipes are 2.5" correct? I want to fix this first and wait and see if the code comes back.

Boone · Apr 6, 2018

Yea, I'll bet that was it. The stock exhaust is 2-1/2". Some of the aftermarket band clamps are very thin and they stretch easily. Torque specs on them is between 35 and 40 lb/ft.

I Bleed Ford Blue · Apr 6, 2018

The clamps that failed are from ford, err ford racing. They came with the ford racing x-pipe/resonator delete. If this solves the problem, I'll go get the pipes welded.

I Bleed Ford Blue · Apr 6, 2018

Bought a new set of butt joint band clamps and a pair of the O2 extenders from amazon. Will try that first and if it works, then great, it will save me a few hundred on a custom tune to fix the CEL.

I may still get a tune done to get as much power out of my setup as I can. Most aftermarket open element CAI's with tune claim mid 30's rwhp gain, ford only claims 23 rwhp and I also have an 87 mm throttle body with it so I know ford left a lot on the table. Throw in long tube headers on top of everything else and there has got to be more in there.

Boone · Apr 6, 2018

I agree.

Boone · Apr 23, 2018

How did this work out for you?

I Bleed Ford Blue · Apr 23, 2018

I put the new clamps on earlier today, and driving home from the doctor, it threw the p 0420 code again. So now I have to put it back up on jackstands again and put on the extenders and wait to see what happens.

I only know what I know · Apr 23, 2018

Just a thought here because I'm not familiar with 420 on these cars. There are a number code strategies where the number of miles you've put on the car doesn't matter. Some situations to pull some codes is based on cycling from and back to KOEO. If after so many cycles the ECU can't solve the problem with the programmed strategy it determines the problem is beyond it's ability to solve and throws the code. It's a good solution to prevent sending people to a shop for a problem that will solve itself but it sucks for intermittent problems and weekend drivers. A good example of where the strategy is useful and time wise fits your pulling the code is during the seasonal changeover of gas from winter to summer. Depending on how often a driver fuels their car and the number of different stations they're using they could be flipping back and forth on fuels that require different A/F ratios. The ECU doesn't evaluate fuels. Just their effects. I don't have the emissions diagnosis manual here to verify this for your car so it's just something to consider.

I Bleed Ford Blue · Jun 18, 2018

Well today I had the car dyno tuned and they fixed the code issue. Good news, I'm getting 425.8 hp and 380.4 tq at the wheels. That equates to 501 hp at the crank with just bolt ons, all motor.

Boone · Jun 19, 2018

Nice!

P 0420 code

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