Not true. The O2 sensors rely on the cats in order to regulate the air/fuel mixture.

 

Whether this works depends on the year/make/model/and whether the vehicle is CA/FED. It works sometimes. However, to answer this question so that you can make a sound judgement, let me explain that not all converters are the same. The reason Ford uses two converters on each bank is because they perform similar but slightly different functions. I don't want to get into too much detail, but I feel I must to properly explain this issue.

You never get clean combustion in an internal combustion engine. As you approach a true stociometric, the heat causes oxygen and nitrogen to fuse together into nitrous oxides. This uses up oxygen that could otherwise be used for perfect combustion, leaving small amounts of unburned fuel. This is why cats are required. But cats require oxygen too, which is tied up in the form of nitrous oxides. The front converters are designed not only to produce a rapid light off, but also to help converter the nitrous oxides back into nitrogen and oxygen, so that the oxygen can be used to finish burning any remaining hydrocarbons and carbon monoxide in the rear cat.

If you remove the front converters, you severely compromise the rear converters ability to do their jobs. Sometimes they will still function well enough to do their jobs adequately, other times, it compromises them enough to set a code. As a general rule of thumb, the older the truck is, the more likely it is that you can remove some of the factory converters without issues. As they get newer, the vehicle are required to meets stricter standards, which means the computers tolerances are stricter as well. Also as a general rule, if the vehicle has a California emission sticker under the hood, it is not worth the chances to try it. It means the vehicle does have the computer that is calibrated to meet California's strict smog laws.

When you use aftermarket converters, you can eliminate the pre converters (not legally however, it counts as tampering), with a single unit on each bank. One has to make certain the replacement unit is powerful enough to replace the factory units however. Also, while at it, one should consider performance. A standard "high flow" converter is really no such thing. The common units, including the top name brands, all use the same 400 cpi ceramic catalyst used by Ford. In short, it means it flows exactly the same as the factory cats.

In order to improve flow, you either need to increase the cross section, or reduce the cell density. We usually use our 1000 or 2000 series converters for this purpose. They use the 400 cpi, but have a 25% greater cross section, and a very powerful catalyst blend that easily meets or exceeds the factory efficiency levels. Plus they are very reasonably priced.

We have Tru-Performance converters available as a special request, but they are cost prohibitive. In order to work as well as a higher density converter, they have to have a richer loading of expensive precious metals.