I own a '99 F-150. It has four catalytic converters from the factory. I recently threw codes for the Bank 1 and 2 Catalyst System running poorly. It was determined that the cats are plugged, so I ordered a set of 49 state legal Magnaflow high flow cats and replaced the rear OEM cats. Today while I was under the truck welding the new cats in place, it dawned on me that this may not fix the problem as the front cats would probably plug first. Of course, the issue could also be the upstream oxygen sensor, but this remains to be seen.

I cleared the code and will wait to see if the issue is resolved, but if it is not, I'd like to just delete the front cats instead of spending more money on replacements.

Update: Seems that deleting the pre cats would be illegal. Odd, since there would still be cats in place. Nevertheless, if replacing both O2 sensors does not solve the issue, I'll just replace the precats. Cheaper than a $25k fine.

 

I was going to post this on AR15.com and I still might in case you check there more often.

Just remove all 4 cats and replace with 2 high flow cats: Magnaflows part #'s 94106 or 94306.

Short answer: As long as your second set of O2 sensors are "down stream" of the cat's you should be fine. If it still wants to throw a CEL Code you need to get a bung to weld in the pipe to raise the O2 sensor to trick it into thinking there is less flow through.

Carl

I'm sure someone else will chime in to help out.

 

I put a set of 94006 cats on.

 

As long as they dont demand you visually need 4 cat converters you will be fine.