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Catalytic converters on a 4Runner

I’m thinking of buying a 2000 Toyota 4Runner with 77K, but just found out that it needs a new catalytic converter (the seller is paying). Could this be indicative of a larger problem with the engine (i.e. burning rich, or weird fuel-to-air ratio)? How worried should I be that this Toyota isn’t what Toyotas should be?

It’s a maybe and maybe not situation. If you know the seller well and you know how the thing was driven, you may have something. The mileage is low, so the cat could have had a rough life with all the short, slow trips. If those trips were taken on roads, the rest of the vehicle is probably in good shape. If it was wrecked and put back together over a long period of time, then it’s not a good buy. If all the paint matches well and all the body parts are aligned, then it could be OK. If you worry about sensible things, you will find a shop that checks vehicles for buyers and have them go over it. You have to tell them what for and agree on a price before they do it. Make sure the owner has a valid title in his own name. If not; stay away from vehicle vultures.

If the delivery date of the vehicle when it was first put into service can be determined it’s possible the converter can be replaced under the 8 year/80k miles emissions warranty.

Since it’s a 2000 model and was likely built in '99 it’s possible this could be a freebie IF the date the vehicle was delivered to the customer was after today’s date or if the vehicle was placed into service as a dealer demo after today’s date.
Nonetheless, it’s within the mileage. The only issue is if the 8 years is up.
Try to look at the maintenance/owners manual and note if and when the delivery date is specified. If it’s mid April or later of 2000 then it needs to be gotten into the dealer and take advantage of the Fed. emissions warranty.

If the converter diagnosis is correct then the converter may have failed for exactly the reason you mentioned; running too rich. Overheating which causes a head gasket failure and/or oil consumption could also cause the converter to fail.
Converters are pretty much trouble free and there is usually a cause behind the failure when one does go bad.

I would like to point out that there has been a rash of catalytic converter thefts, and these Toyota trucks have been a favorite, due to there high ground clearance. Maybe the truck was a victim, and a cheap aftermarket was added that does not meet the requirements of the truck. Not trying to scare, but just throwing an idea out there.

an improper diagnosis can lead someone towards thinking a cat must be replaced when in fact it is something else.

the suggestion to take it to a independent mechanic is probably best (not necessarily a toyota shop, but one that works in imports)

Thanks – it is under warranty, so it’s being replaced for free, and it’s the Toyota dealer that made the diagnosis of bad cat. And I trust the seller, but she’s the third owner of the vehicle, so I don’t necessarily know how it’s been driven.
Now that it’s been inspected by the Toyota dealer’s mechanic, is there anything else I can do to find out whether the bad cat is the result of a bad engine?

Yes, a good mechanic.

After more research, and help from you good people, I’m hearing that the bad cat could be caused by an untold number of things: engine misfire/running condition, defective valve seals & piston rings (oil consumption), vacuum leak, plugs and plug wires…
Maybe this is not the right Toyota to get into at this point.