P0420 FZJ80

[KFZJ80]

Hi Guys -

First time post here. I saw a couple related threads but nothing recent so I figured I'd bring this up again.

I just picked up a 1996 FZJ80 and am working on some baselininf. I got a P0420 code a couple of weeks ago and wanted to start by changing out the O2 sensors per the service manual. Next step would be to investigate any exhaust leaks. The cats seem to be working based on temp readings but not confirmed. I brought it in to a local shop and they recommended a full exhaust system replacement. I think this is overkill at this point and they just didn't want to deal with the surface rust.

Anyone have any advice here? Is the O2 job simple enough for a novice mechanic like myself? I'm in Brooklyn and don't have much space to work on the truck so a local mechanic recommendation would be great as well. I saw the list of mechanics by state but limited options in the NYC metro area.

 

[Dragos80]

Very easy given there is no rust on the nuts.

 

[KFZJ80]

Thanks, Dragos. I'll check it out but have a feeling they'll be pretty tough to get off. Will try some P'Blaster. May also measure the resistance at the connectors before I change them out.

 

[DirtScaresMe]

I use aero-kroil (instead of pb blaster), brass drifts to provide some encouragement, and a pencil propane torch to heat. I think I've used vice grips a few times when things got bad, and when things got real bad I've turned a nut into a rectangle with a dremmel friction wheel and gone ham with leverage.

 

[thelal]

P0420's can also be 'hole' in exhaust between headers and O2 sensor

 

[KFZJ80]

Thanks, Thelal. Yea my O2s are fine. I suspect a leak in the exhaust somewhere. Maybe a gasket or some small cracks. I threw a bottle of Cataclean in and haven't gotten the code in a few hundred miles. Just a temporary fix. I'll probably do a new full exhaust sometime soon.

 

[bicycleagent003]

A common leak point in the exhaust is the crotch of the Y pipe coming down from the exhaust manifolds. I had a small leak there which I diagnosed by spraying it with really soapy water right at start up on a cold motor and exhaust system.
If you do have to take off the O2 sensors (it's a good idea with these vehicles at this age, IMHO), Irwin sells a really good nut remover set which is relatively cheap. It took off badly rounded nuts off quite easily. Some users replace those nuts with brass, I used stainless steel. In any case, I'll probably replace the whole system before I have to replace the sensors again, so the replacement hardware doesn't matter all that much.
Good luck.

 

[thelal]

I suspect a leak in the exhaust somewhere. Maybe a gasket or some small cracks.

I've a leak for years and just keep putting on exhaust putty (its where headers meet the twin pipe) and that lasts for several days and then blows out. Tried various mixes/varations but no main difference.
Will look to replace complete exhaust with stainless including hangers so fix once and done

 

[IronCladLou]

P0420 is simply "catalytic converter efficiency less than some threshold". Typically (at least on my 2001 Tacoma), this is determined by the difference in readings between the O2 sensor upstream of the cats and the one downstream. All it means is that the efficiency of the cats have dropped below some (most of the time) arbitrary point. It doesn't necessarily mean you have a problem. On my Tacoma I replaced the O2 sensors (which didn't help) and then found that Toyota raised the threshold for what is considered adequate efficiency to match California requirements (49 state was much lower). So, in the end, it is really no harm, no foul. Hopefully this applies to 1FZ-FEs also...

IMHO, I would not pursue replacement of the cats unless you really think you have a problem.

 

[izzyandsue]

Before you start pulling parts out, I recommend the exhaust leaks. Easy way to do it is to blow air into tail pipe, and use soapy water spray bottle on joints and pipes, will be obvious. I used a shopvac on blower mode loosely into the tail pipe, so it is not too high pressure air but enough to create bubbles in the cracks. I eliminated by 0420 this way, found the leaks, replaced the gasket, and problem never came back.