Is it common to get the P0420 code after installing longtubes headers and high flow cats? It's the "P0420 OBD-II Trouble Code: Catalyst System Efficiency Below Threshold (Bank 1)" code. I know a custom tune can trick out these codes, but if this is a common occurrence, why bother getting catted mid pipes with long tubes instead of off road midpipes?

 

Yes, it's somewhat common. The location of the downstream sensors can be critical, and you may need to do the Gotts O2 mod.

https://www.f150online.com/forums/ex...-mod-pics.html

 

Thanks, I will have to try that mod asap. I guess my bigger question was, if it is such a common issue why go with catted mid pipes that will likely throw codes and cost more?

Also, should I assume the location of the rear sensors is what is causing my problem? How would I know for sure it's not a catalyst issue or a leak or stuck injector or any other problem that can cause the code? The system is brand new. It's Stainless Works 1 3/4" longtubes with high flow cats on my 2008 5.4L. I did have a leak at a cat so I had to rotate a clamp (the bolt of the clamp was lined up with a slot on the pipe so it wasn't squeezing right). I think I got the clamps all squared away, I'll have to check the bolts on the headers (that should be fun getting back to them). I'm assuming the catalyst is fine, the cats are literally brand new. I do want to change out my injectors soon, they are original with 110,000 miles on them and are developing that slight tick.

I really just want to make sure that tricking the sensors into everything being fine won't cause any issues further down the road.

 

All those rear sensors do is monitor the cats. All fuel/air parameters are controlled by the front O2's.

High flow cats frequently do trip the low efficiency code.

 

"High flow" cats may or may not actually be efficient in doing their assigned job.


If you have mandatory emissions inspections and the inspector sees the anti-foulers during his inspection, you will fail.

 

I installed the non foulers the other day and after a drive the cel came on again. First thing I noticed about this "mod" is the sensors bottom out in the non fouler. In other words the thread length of the sensor is longer than the non fouler and will not thread in all the way befor it hits the inside lip of the non fouler. Drilling it out with the 1/2" bit does not allow it to thread in further. A larger bit would compromise the threads of the non fouler and I believe it still wouldn't allow it to thread in any further. Anyhow, that was my first take away from this. Secondly is a strange one. When I pulled the sensors I noticed they were pretty heavily caked in soot. Now I always understood longtubes to tend to cause engines to run slightly more lean, however this symptom of carbon would tend to show a rich ratio. I confirmed this is recent build up because the same soot is starting to collect on the insides of the exhaust tips. I think my takeaway from this is I will need a tuner, and if the cel persists, have them disable the rear O2s. I'm pretty sure I'll end up with an SCT X4 from 5 Star Tuning. I've heard great things about them, and hopefully some nice tunes will really open up the potential of these longtubes.

 

No f*ckin surprise there. Whoever thinks you can fool the emission system by putting a spacer in there is an idiot. The rear O2 sensor does not "just monitor" the O2 sensor. It lets the ecu know if it is running lean or rich. I had the same issue in my 370z when doing hfc's. you have to re tune the truck and get the 2nd bank of 02 sensors turned off. At this point you are only relying on the 1st set of sensors for the a/f ratio. Since you have cel on you are running to lean which will burn your motor up pretty quickly.

 

I figured as much, however if I was running lean I wouldn't be seeing the amount of soot build up on the sensors and inside my tips that I am getting. I also believe the cel is not from lean or rich in the front o2s, but doesn't "see" the cats installed read by the rears. I had a similar problem using the MagnaFlow hi flows I had in previously.

 

WRONG.

The FRONT O2 sensor monitors fuel trim, the REAR O2 sensor monitors the catalytic converter. The rear sensors in this era of Ford's trucks has absolutely ZERO to do with either fuel trim or A/F ratio.

The anti-foulers, when executed properly, DO indeed work to avoid cat efficiency codes. You just have to know how the supposed to work and how it might be fooled.

 

You are Wrong. 2nd set of sensors to tell the ecu if the vehicle is too lean or rich. That's how the primary knows where to adjust, otherwise how would the vehicle know if it had a lean or rich situation?

When end you get a hfc and install it the catalyst is smaller.....meaning less efficient. Vehicle sees that the 2nd set of o2 sensors is reading beyond its threshold.....it then leans or riches itself but it won't be able to register the change because it sees no difference due to the lack of input.

first set of o2 sensors are wide band o2 sensors, second set are narrow band. Once you change the filtration or catalyst the sensors are then over saturated with emissions or voltage however you want to look at it. When the ecu interprets this it sees a bad catalyst.....

so so again you are wrong

 

http://www.dummies.com/home-garden/car-repair/how-to-assess-trouble-by-checking-your-spark-plugs/

not saying saying your a dummies lol. Rich condition proven

 

Sorry, I'm with SHO on this one. The front sensors determine lean or rich and adjust accordingly. The rear sensors are only to monitor cat efficiency as mandated by the EPA for OBD2.

 

That's the way it was explained to me by a tuner at a very reputable performance shop.

 

Sigh... Go back to school...




Then, either he didn't know what he was talking about or you misunderstood him.

Go learn how the OBDII system operates the fuel control and the catalyst efficiency checks on Fords, then we'll continue this conversation. The reference manuals are FREE at www.motorcraftservice.com Anything further from you on this subject trying to "prove" your point is a waste of bandwidth.