Clogged cats diagnosed on 2003 w/ 205k miles. Fixed.

[Billy bee]

Hey gang,

Got a damaged but drivable ZHP last year for the engine and 6-speed for a swap into my E46 wagon. Really excited about the swap.

However, I had a number of codes and a troubling drivability issue. Once I fixed massive CCV and intake leaks, the car would feel sluggish up to about 5000rpm and the go into limp mode showing 28A2 code on INPA. It would also show the EML light. Everything pointed to MAF, but a test of the MAF showed it was operating properly. Looking at the bank 1 and bank 2 O2 sensors showed high voltage on the upstream sensors, rather than switching from .1v to 1v. That indicated a rich condition. Something wasn’t right. I suspected the cats might be clogged. So, I ordered a $40 exhaust back pressure tool on Amazon. At 2500 rpm, both cats showed excessive back pressure, over 4psi. Bank 1 was worse than bank 2 and the spark plugs on 1, 2, and 3 were all wet with gas. Clearly running rich.

So, we had some good used cats from a parts car laying around and swapped them out. Voila! The car is running great. Pulls great to redline. A lot of people complain about replacing the cats. It’s really not too bad. We drew the refrigerant out of the A/C system and moved the A/C hoses and compressor out of the way. Also removed the engine mount from the block. Easy access from below for 14 of the 16 nuts. I don’t recommend changing the cats unless you know for sure they are clogged. The only way to do it is with the back pressure tester, worthwhile testing the upstream and downstream O2 bungs so you know the clog isn’t in the resonator or muffler.

I’m gonna pull the injectors and send them out to be cleaned and blueprinted. I suspect a leaky or faulty injector or two caused the cats to clog. Poor fuel atomization makes for poor burn propagation and wet plugs. Don’t want to ruin these cats…

Hope this is helpful if anybody else is having similar codes and issues.

—bb

[John in VA]

An overactive fuel pressure regulator can cause cat damage. too. This happened on the E28 & E30 - FPR would default to full blast & cause running/idling issues & cat contamination.
I don't even know if the E46 has the FPR!

[Billy bee]

I don't even know if the E46 has the FPR!

They do. The fuel pressure is regulated by the fuel filter. We have used the E46 filter on our 2005 Hyundai Elantra (swapped with a Tiburon V6/6-speed) 24 Hours of Lemons car where we were having problems with the FPR. It's a good system.

You raise a good point about fuel pressure. I did not cover a lot of the diagnosis steps we took to get to replacing the clogged cats, but fuel pressure was certainly one of them. We checked pressure and flow at the rail after installing a new fuel filter. Both were good.

Thanks,
Bill