4122, 4121 Just great!!!!!

I'm pretty sure that you get 4121 when you either have a bad cat ecu or the cat ecu is unplugged.

4122 is the real thing, but I don't know if it is 100% reliable when you also have the 4121 error.

It's just 2 little bolts to swap cat ecus from side to side, which is a standard test *if* your cats weren't actually glowing a dim red.

 

FWIW, and this is unrelated to the thread, but Champion plugs suck. Use an NGK DR8EIX.

 

+100!!

 

Try swapping MAFs from side to side. To see if the problem goes to the other side.

Try some techron injector cleaner too. It is possible to run lean if the injectors are not atomizing correctly.

 

One or the other.... your plugs don't look very rich .


Basically if the fuel is not atomised well, it doesn't burn completely and will be lean in the cylinder. So it will be rich in the exhaust because that unburnt fuel is escaping cylinder combustion and burning up in the cat.................... I hope that makes sense...

 

I had check engine lights coming on every few days and then going away ... one night I, after a fairly "spirited" mad-half-hour that I occasionally have I got back and looked at the cats. 1/4 was glowing. Damn.

I switched out the O2 sensor on that side and put new NGK plugs all around. It runs so much better now, no check-engine lights in a month and I use it very frequently.

I'm sure i've shafted the cat on that side but I'll deal with that when I deal with it.

 

No, not so far. I've driven it a lot in the recent weeks and when it's dark I always check to look if there is anything awry in the rear.



I'm sure it's done the cat no good though being so hot. I'll be putting either an Xost or Tubi on later this year, and will likely put hyperflow cats on as well, so I'm not overly worried if it's done it damage, providing it doesn't do any further damage.

 

A couple of consecutive Techron FI cleaner treatments !! It will do you some good no matter what, especially if you don't drive your car much !

 

+1, Goth is right on. This may not be the problem...but then again it could contribute. A good injector cleaning is high on my 'to do' list, along with plugs. Slightly on topic...any tricks or tips to replacing the plugs? Are standard tools all that's needed?

 

The all-whitish ground strap shows you that either your spark plugs are too hot or that your timing is too advanced (if the correct spark plugs are in use).

The black deposits on your base ring show that you are too rich.


Your O2 sensors are ignored at WOT, but are probably your problem for your idle (when hot) and mid-range. Less likely causes could be bad water temp sensors (348's have 4 of them), MAFs, FPRs, etc.


Might as well try a colder spark plug before going to the change in timing, too.

 

WOT is Wide Open Throttle. O2 sensors are ignored at WOT.


What's your resistance in Ohms between the extreme pins (#1 and #6) behind your black MAF data cables?

 

Those numbers on the MAFs would *not* cause an otherwise perfect 348 to overheat the cats. Especially on your 5/8 side. That's a good number for not being rich.

Your problem lies elsewhere.