2003 Expedition
 

I have a 2003 Expedition. I have been told there are four catalytic converters on this Eddie Bauer edition. Its a V8 5.4 liter engine. Anyone have any information on this... Its driving rough smelling like gas???

.....and the first thing you want to do is replacing the catalytic converters?
I would go slow on that, I would go from cheap to expensive not the other way around.
Is the CEL light on? What are the codes?

Fix the rough running first. Do the usual tune up things. Plugs wires, coil pack, airfilter, fuel filter, clean MAF sensor, clean throttle body, check for vacuum leaks and check for fuel leaks.

After the tune up drive the vehicle for a longer distance so it gets nice and warm and can burn off some deposits.

If it does not clear up you may have to look into O2 sensors and other stuff.

2003 Expedition
 

Thanks Bluewind... We do know that there is a problem with one the number 5 cylinder.. and we have replaced the fuel filter and ONE of the oxygen sensors. AFTER doing that we discovered that it was blowing vacuum hoses?? So for us it was a guess about the catalytic converters.

Since your vehicle has coil on plug ign system try switching #5 coil with one from the other side of the engine and see if the miss has moved to the other cylinder.

It is blowing vacuum hoses. You mean the intake side gets pressurized? I am trying to see how a plugged exhaust system will pressurize the intake side. There is one connection: the EGR system. If the EGR valve does not close it could allow pressure to enter the intake side.
There is another connection: the PCV system. The volume inside the crank case will not change since one piston going down is offset by another piston going up. Unless you have major blow-by the increase in temperature should be slow enough not to cause pressure on the intake side.
Is there any back firing happening?

Follow Hanky's suggestion and closely inspect the EGR system and let us know what comes of it.

2003 Expedition
 

Thanks Bluewind and Hanky. We will try out your suggestions and get back later...