If it is getting tired, it cannot do the job without the help of the pre-cat. If your main cat is in good shape, it will clean the exhaust nicely all by itself once it warms up. The car will run nicely without the pre-cat, it will just be a polluter until the main cat gets warmed up and comes into duty. Between the two cats (and the pipe that comes with them) you are already back to about the rear axle, exhaust system wise. Note that the catalog listing for the main cat shows a section of pipe, also. It does most of the work of cleaning the exhaust but it takes a while to heat up and start working, so it allows the engine to be a polluter in the period shortly after startup - the pre-cat cleans up the cold start stuff but is fairly light duty, the main cat does the bulk of the work. The second cat you list is the "real" catalytic converter, the big one. The pre-cat basically replaces the downpipe that used to connect the manifold to the main exhaust system. It is sometimes referred to as a "pre-cat" because it is prior to the main converter and starts the job going promptly, so to speak. This helps to give the engine/car a good emissions rating for cold start performance. It is a small catylitic converter close to the engine (source of heat) so it warms up very quickly and rapidly starts catyilyzing the exhaust nasties. The first cat you list is the one that bolts to the manifold. Ditto on knock sensors - knock on wood, I have never had to replace one and I run my cars to very high milage. Unless you have indications of failure, keep using it - they usually last a long time. The Volvo 740 Turbo wagon I had went to 195,000 before I sold it, still on the original cats. My Mustang has 150,000 miles on the original cats and is doing fine. Has anyone on this board used this type of service?įirst, before we discuss the cats - what makes you feel you need to replace your cats? Do you have engine codes saying you have a problem? Until you get codes, run what you have, in my opinion. I'll be selling the old one for scrap to offset the cost. I was thinking about maybe doing a knock sensor too but I haven't made up my mind yet. If you did the job, what did you break and have to replace while you were in there? I already need a new ground strap so that's on the list. Who has done this job? Do I need to pull the manifold or can I simply unbolt the cat below it? I'll replace both sensors while I'm in there as well, as it makes no sense to try and muscle the old ones out at this age/mileage they are past their service interval anyway. It looks like there might be 2 but it appears that there are only sensors fore/aft of the first one, making the choice easy. I'm confused as to if there are 1 or 2 on the car. At 120k miles it's time for a cat on my 2007 sport.
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