spark plug non-fouler issue

I attempted to do the spark plug non-fouler fix for my P0421 error. The error code hasn't come up in a week since I cleared it last week.
I bought this part, NAPA 7302442, 18mm spark plug non-fouler. http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?R=NDP7302442_0375753140
I drilled it out with multiple drill bits until I got the 1/2" bit through. Then, I removed my O2 sensor and found that it would not fit through the non-fouler so the threads of the O2 sensor screw into the non-fouler. I have a Bosch O2 sensor. I am guessing, and hopefully someone can validate it, I need to drill out more material from inside the non-fouler. It looks like, just from eye-balling it, that I am almost going to have to drill out so much material so the non-fouler is going to be very thin at the lower threaded area. I know I got the right size non-fouler because it fits in the O2 bung.
The other question I have is does exhaust gas still have to flow through the non-fouler to the holes of the sensor? It looks like there will hardly be any space for gases to flow up to it.

Also another issue. When I had the hood opened, I noticed one of the bolts that hold the exhaust manifold to the cylinder head broke off. Just the threaded part of the bolt is left. There are eleven bolts so I am going to wait on replacing it. I had to remove it back in January in order to replace the gasket between the pre-cat and the exhaust manifold. I torqued all the bolts back on with a ghetto-cheap torque wrench (ft-lb readings are gauged with a metal pointer). I'm guessing the pre-cat may be clogged/bad because it caused enough pressure to blow the gasket. Now that the gasket is replaced, I'm thinking the heat is higher than normal and so the exhaust manifold flange is getting hotter than usual and it is expanding more than usual and the bolt head popped off, or I torqued it on a bit too much.
I'm guessing I need to replace the pre-cat or put in a header.
Any thoughts?

I had this issue or what sounds to be similar. Think you have a universal o2 sensor, the oem ones are a tad thinner to where it will fit. I ended up picking a oem sensor at O'Reillys for the cheapest. Fit perfect never any issues.

Thanks. It's a Bosch universal O2 replacement. It comes with a splice kit to work with any O2 plug.
I just replaced that O2 sensor about two months ago.

The whole point of the nonfouler is that it pulls the o2 sensor out of the exhaust stream...it tricks it into thinking the gasses passing are clean (because of the cat) when they are not. So, it doesn't really matter if the exhaust gasses have a way to flow to the sensor...

As for your header bolt, there's no way that your cat could have clogged bad enough to blow the manifold seal without stalling the car. It simply won't run if it is choking on exhaust. Are you sure the bolt head was actually a bolt head and not one of the threaded studs? IIRC, the header bolts are a combo of traditional bolts and studs that stay in the head and just have a nut that comes off. Maybe a nut worked itself loose and came off. That would be an easy fix.

The non fouler needs to have just a small hole in the one end to function properly. I remember installshied said he drilled out both of them and it didn't work. It needs to see just a little bit of exhaust gas to function properly.
If you just set the sensor in the engine bay somewhere, that won't work either. It needs to see some exhaust.

That sensor will get just a brief wiff of your exhaust. I also can't tell you how many bolts I'm missing or broke the head off in my bay.

I tried the universal Bosh o2 sensor once and it does not fit it the non-fouler.

MazdaSpeeder said:

? IIRC, the header bolts are a combo of traditional bolts and studs that stay in the head and just have a nut that comes off. Maybe a nut worked itself loose and came off. That would be an easy fix.

Click to expand...

That's right there are 9 bolts and 2 threaded studs and have nuts to lock down the exhaust manifold flange. The end is broken off with a jagged edge and no threaded length is left to attach a nut. I'll just replace it later.

The elasticity of the bolts is greater than the thermal expansion of the manifold. If the head is missing (and not a stud that hte nut fell off) or a broken stud, then it was overtorqued. You did use a torque wrench to install them, right?

correct that you'll stall the engine before you "blow" the manifold gasket. however if the manifold isn't bolted down correctly (with proper torque) it could certainly cause a leak, causing your O2 sensor readings to be off, causing the engine to run out of stoich, causing your PO421. Fix the manifold, O2s will read actual engine output, engine will run right, no more P0421 like magic. Fix it right instead of ghetto-rigging workarounds spending 10x the energy of just fixing it right.