This is strange to me. It seem like after my car is running for a long period of time, it will start bucking and eventually lose power. However, if I turn off the car before it completely lose power it will start and continue running fine again. check engine light is on, however its for CAT. Can a bad cat cause me to lower power or this is a bad coil problem. Thanks for any help

 

Yes, but is that a result or a cause in your case?

Which codes?

Engine? Year? See:

 

the code is p0430 and 2000 Stype v8 4.0

 

Not great news. Have a look at the fuel trims at idle and 2500rpm (in Park).

It's worth putting car info in your User CP.

 

my car info has been in CP for quite sometime unless its in the wrong place.What do you meant by not great news

 

It helps if in signature in CP.

May just be a bad cat but they're fairly rare and often due to a fault elsewhere.

 

I too believe it sounds as if one (or both) of your catalytic converters may be becoming clogged. My 2005 STR had CAT issues but there were no problems elsewhere. My case is not typical and most CAT failures are caused by an outside issue just as JagV8 mentioned.

The initial indicator of clogged CATs on my car was a small loss of power during full throttle and the restricted performance light would turn on sporadically for a few moments. Next, at full throttle, my car would "ping" and sounded like there was no oil in the engine. Next, at full throttle, I got random misfire codes and eventually CAT efficiency codes. Just before the CATs were changed the car barely ran and the CAT literally broke up inside and white flakes came out the exhaust pipe. At this point the max rpm of the engine was approximately 3500 rpm.

 

 

Ok the culprit is the cat. However, I was at the muffler shop and they suggest I put in a universal Cat. I was on board with it until I saw it was so different from the original in which they would place the O2 sensor in the pipe before the Cat whereby it sit in the original. Would this hamper the way th system works. I dont think so in theory but I could be wrong.

 

Out of interest, what mileage is on the car?

 

I just register 100K miles a week ago

 

I would stick with aftermarket CATs with OEM fit. You can find them on Ebay and such - about $200 - $250 each.