07NiteMare

I have an 07 F150 that I am in the process of revamping the factory exhaust to get better flow. This particular model has four oxygen sensors and two cat converters. The configuration is a sensor just after connection to manifold then cat with sensor on cat. This applies to driver and passenger side exhaust. Just behind cat the two come together and go tomuffler. I most recently gutted both cats on my truck. In the process I accidently nicked one of the wires on the passenger side upstream oxygen sensor. Shortly after this mod the check engine light came on(cel). There were two codes which were indicating bad oxygen sensors ( upstream and down stream) both on passenger side. I was advised at parts store to replace front sensor and that should cure the problem. So I bought a new Bosch sensor. My victory was short lived. I drove the truck for about 100 miles when the light came back on. My question is by gutting the cats did I create a problem of not enough backpressure? I am trying to figure out what I need to do to get rid of my cel blues. Preferrebly the cheapest fix the better of coarse considering I am already in the whole an oxygen sensor and those things aren't cheap!

bradseabridge

Back pressure is a myth. Your problem is directly related to gutting your cats. They were there for a reason, now you know what the reason is.

Sent from my iPhone using F150 Forum

07NiteMare

So basically my best investment would be a complete aftermarket system including cats (and no dogs Hehe). Just a little dry humor. How come no codes emerged for driver side sensors?

otto457

Read this about back pressure and engine function:
https://www.f150forum.com/f11/exhaus...re-myth-78102/

First get the upstream O2 sensors in fixed. The fronts do all the work monitoring a/f ratios so they need to be in good shape. The rears monitor cat function, and can be fooled be the Gotts O2 mod or a programmer.
By gutting the cats your velocity is decreased. Either go to high flows or pipe and get a custom tune to account for the change to the cats.

07NiteMare

So Otto when you say high flows your speaking of the cats right. I didn't know if they made some type of high flow sensor or something. This is the first time I've did any type mod like this to an fuel injected vehicle. Im so use to working on older vehicles without an OBD system. I guess I got too excited thinking about how much I could open the exhaust up. Also does anyone know of a good bolt on exhaust with cats? I've been looking and all the ones I find are cat back. I was hoping to go with dynomax but it doesn't seem that theyhave one.

otto457

Check the new code. If it is a cat insufficiency code, that can be dealt with. If it's an upper O2 sensor fault, that needs to be fixed correctly.
The problem with the gutting the cats is there is now more area for expansion of the gases and this lowers velocity. A properly functioning cat only adds .3 lbs resistance, not enough to eliminate them for performance.
It is illegal to sell a vehicle without cats, so if you ever want to get rid of it in the future, it will need high flows. If you plan on driving it forever, just do the Gotts O2 mod on the rear O2 sensors and replace the hollowed cats with pipe. Sometimes even with high flow cats, the CEL from the rear O2 sensors will still be there. The rear O2 sensors then will need to be fooled or turned off with a programmer to stop a CEL. Modifications to the cats need to be accounted for with custom tuning anyways so go the programmer route.
Here's what I'd do:
Order 2 Magnaflow 94106 cats from performance peddler (use code clubgp or veedub for a discount)
Get them welded in place of the hollowed cats, and place the rear O2 sensor an inch behind them.
Order a SCT x3 or Gryphon with custom tunes to account for the cat changes, and a CEL for cat insufficiency comes back then get them turned off in the tune.

There are a few that make replacement cat systems but they aren't any better than stock and are expensive.

07NiteMare

Just curious Otto, what kind of mileage are you getting? Right now I only get about 18 and that's if I baby it. I was hoping to get somewhere in the neighborhood of 20. I figured that be pretty good for a 4 wheel drive.

otto457

With my 2-vavle 5.4, I average about 19 mpg in the summer and 17 in the winter. That's a mix of driving. If I'm on the highway locked in at 55 mph for a long time I can get above 20 mpg but that usually never happens due to my route. I hate all the little towns every 8 miles that make you slow to 35 through them and then have to get back up to speed.

alfack

I just did this to my truck, because one of my cats was clogged and I was getting the P0420 CEL code. I went with the Magnaflow 94306, as I am not a loud exhaust freak and they were supposed to be a little more quiet than the 94106. I had the guy weld the o2 sensor bungs behind the cats as seen in the pictures, below. This took care of the problem. No more codes. By gutting the cats, you made it so there is not enough delta between the front and rear o2 sensors. Print these pictures out and show them to your exhaust guy, if he has a hard time coming to grips. Also, if you go with the 94306, you may need o2 sensor extension harnesses, like I did.

07NiteMare

Thanks for the pics. That gives me a real good idea of what should be done. Im still curious as to why the first and second time I had the codes read off the truck it dealt with the sensor up stream but the explanation that the computer gave said that it could be a result of faulty cat.