I swapped in a built motor about month ago. Broke it in and decided I would slap on the procharger on friday sept 5...

After I slapped on the procharger the motor didn't seem to be as fast as it should be. Drove it this way for 2 days, gave it some revs, etc. and finally mid-day yesterday I developed a nasty rattle coming from catalytic converter/collector area when the engine was cold. It is not the heat shield but something internal it seems. Catalytics are 120,000 miles old (original ford).

The funny thing is when I developed the rattle I probably gained about 75 horsepower and the truck feels much faster than it did on friday and saturday.

My question to you is, is it possible I had a clogged cat and whatever was clogging it has now come loose and is rattling around inside freeing up all of this extra horsepower? Is there anything internal to the motor that would cause a rattle through the exhaust when the engine is cold? Valves?

Thanks.

 

In the Ford manual there is a test you can do using a pressure guage but I have no idea what they would be witht the procharger. You may have to disable it. Also Did you have a tune done? Either caned or custom. That could be the issue. I am sure other will jump in on this.

 

Yes I had a mail order tune sent to me for the new motor and the truck currently has no driveability issues. Planning to put it on the dyno soon to get a real tune but it is running great.

Just wondering if my clogged/unclogged cat theory is sound.

 

colin could be the cats are clogged, If you need to swap them out make sure to check out the OBX headers for around $500 on ebay, have high flows put in place of the resonators or just run 02 simulators


they are stainless and are replicas of the dynatechs, glad you got the new motor under boost finally

 

They look pretty sweet and for a good price. I'm just wondering why they list the headers working for a 5.4 and 4.6. Shouldn't they be slightly different?

 

just the piece for the EGR is different, the ones I've seen on the 4.6 have fabbed thier own pipe form the header to the EGR valve.

first thing I would do is take the truck to a muffler shop and have them test the cats (most do it for free)

 

could be a bad cat that with more pressure applied broke the honeycomb and thats the rattle. I would get new cats on, 2 high flows since you are S/C anyway. Any exhaust shop can do that.

 

My cats rattled once my truck got driven more (after it became mine). I had the serial tag on the cat itself rot off and fall onto the heat shield and it rattled somethin fierce, drove me nuts until I was poking around with a screwdriver and pushed it out! Check that first.