2003 Yukon XL 5.3 Clogged Cat

[Misfitoyz]

I am brand new to posting on forums, but I have used much info from them. I have a 2003 Yukon XL with 126,000 that I bought recently. It had been sitting for 3+ years. It had NO power and could barely climb the slightest grade. It started and idled fine. The check engine light was on and it had 2 codes, random misfire and mass airflow sensor out of range. I decided to replace the MAF and it had no affect. 

Since it has 2 separate cats, truck still ran ok at idle

Here are the specs before repair:

fuel pressure - 45psi - Increases if i remove the regulator vacuum line

Vacuum at idle - 14 - 15 inhg fluctuating. 

replaced:

air filter

MAF

MAP

Fuel filter

Plugs

Wires

All with no affect.

Pulling off the coil pack leads one at a time, the pass side seemed to have less affect than the drivers side. 

Threw in the towel and limped it to my local garage. They confirmed that that it was a clogged catalytic converter on the passenger side. 

I replaced it, and now all seems fine. It is not as obvious with 2 cats as it is with one.

I'm not sure if the sitting around corroded the cat or the fact that they would start up and idle the truck for long periods during it's storage.

Just thought this info would be useful to some else.

Now I get to find out what else is wrong......

[AaronIROCZ]

You should think about replacing your intake gaskets too, my 2002 Yukon Denali were bad and it seemed to run fine but a rich smell out of the exhaust and had cat efficiency codes for clogged cats from the leaking intake gaskets.