removing cat on lly

[HELENA TRANSMISSION]

i was wondering if anyone has removed there catalytic converter from an lly.pro's and con's of doing this mod and will it set check engine light or cause damage?what about warranty issues?is it even worth doing or will a downpipe back exhaust system be sufficient.

[More Power]

The cat itself is pretty efficient, due to GM increasing the surface area of the internal structure by a significant amount over that used by the LB7. Where a cat (this or any other) can become an issue is a few years on down the road. Light-duty use can cause some restriction to develop over time, caused by an accumulation of unburnt soot. HD use tends to keep the cat cleaner and more free flowing.

Deciding whether to remove it is a personal decision. It is a required emissions component. However, it's doubtful removing it will affect the operation of the engine control systems, but could certainly complicate a warranty issue involving an emissions concern.

MP

[Rick_R_04LLY]

After about 1000 mi on my mid year LLY, I had a Magna Flow XL series exhaust installed. This is a straight thru 4" system with a small-perforated muffler about one foot long. No CC.

Immediately started getting EGR codes 401 and 404. Dealer said EGR valve was no good but there was a possibility that the decrease in backpressure was causing the light to come on. The light came on once a day or so

[Kennedy]

I've seen 15HP across the board by adding my 4" system without cat.

The CA emissions trucks seem more stringent and prone to setting codes. General Federal trucks seem to be fine.

Now, the thing is, CT/MA/ME trucks and possibly NY and other Eastern states seem to follow the CA emissions...

[Rick_R_04LLY]

Maybe it's just me but the truck seems a little slugish now. Does not have the pop either from a standing start or on the highway.

How did you determine the 15hp improvement?

[Kennedy]

Originally posted by Rick_R_04LLY:
Maybe it's just me but the truck seems a little slugish now. Does not have the pop either from a standing start or on the highway.

How did you determine the 15hp improvement? Line 3 in my signature. For the record, this was without a chip either.

I am currently running no CC, and my 4-5" system. I also have been working on disabling the EGR without any physical modifications...

[CHVYMAN#9]

I HAVE AN 04 LLY AT WORK RIGHT NOW WITH P0401 AN P0404 AND IT ALSO HAS THE MAGNAFLOW STRAIGHT THROUGH SYSTEM. GM TAC TOLD ME NOT TO ATTEMPT REPAIR WITHOUT THE STOCK EXHAUST SYSTEM. I WAS TOLD BY CUSTOMER THAT HE RAN THE EXHAUST FOR A LONG TIME BEFORE THE SES CAME ON.(NOT SURE HOW LONG). WE REPLACED THE EGR BUT THE CODES DID RETURN. SO I TOLD HIM BEFORE WE COULD GO ANY FURTHER THET WE NEED TO REINSTALL THE FACTORY STUFF AND SEE IF THE CODES RETURN. KENNEDY HAVE YOU BY CHANCE CHECKED TO SEE HOW MUCH BACK PSI THE FACTORY EXHAUST MAKES? IT SEEMS TO ME THAT WHEN THE CODES SET THE EGR IS AT A VERY OPEN POSITION(LIKE IT MAY NEED BACK PSI TO HELP IT CLOSE FASTER)AND WHEN YOU CHECK IT IT IS OK.WOULD LEAVING THE CAT ON CAUSE TOO MUCH RESTRICTION FOR CHIPS? WHAT WOULD HAPPEN IF SOMEONE USED AN EXHAUST BRAKE? KENNEDY YOU SEEM TO HAVE THE RESOURCES TO EVALUATE THIS. COULD A MUFFLER BE DESIGNED TO GIVE ENOUGH BACK PSI TO MAKE THE EGR HAPPY? YET BREATH ENOUGH TO MAKE GOOD POWER. IT ALSO SEEMS THAT THE CODES ARE SETTING AT IDLE,AS IF WHEN THE SELF TEST OCCURS.LET ME KNOW HOW THE EGR DISABLE WORKS OUT THAT YOUR WORKING ON. THE EGR USES A WORM GEAR TO OPEN BUT RELIES ON SRING TENSION TO CLOSE IT. COULD A BIT STIFFER SPRING ON THE VALVE BE THE ANSWER?(MAYBE COMPENSATING FOR THE LOST BACK PRESSURE).THE END CAP ON THE EGR LOOKS LIKE IT CAN BE REMOVED TO GET AT THE SPRING,DON'T IMAGINE IT SHOULD BE THAT MUCH STIFFER JUST ENOUGH TO COMPESATE.WHAT DO YOU THINK JOHN?

[olimaxx]

i bought a 05 and put the RBP exhaust and juice/attitude. wow incredible power. i run 35's on it with a 6" lift .my codes would come up and i talked to both edge perfomanc and rbp and they said i needed to put the cat back in. it was flowing to much air. now one thing i noticed is that if i warmed the truck up for about5 to 8 minutes it would not error, but i had rbp put the cat back because i did not want have to warm it up every time. any q's 714-943-7206
'

[Kennedy]

CA emissions has their own spec, and the NE emissions for NY/VT/MA/ME are also their own little group.

These emissions groups can often find their way to dealers in Federal emissions territories. I know of a 2002 Dmax nearby with the CA emissions...

[johns d-max]

O4' LLY, 10,000 miles, no cat, louder exhaust, no problems, no code, very audible turbo whistle at idle without the cat, more like a constant hiss, but it sounds good.

[turbo lcc]

Are you guys sure there are no codes?? My code reader says no codes but my predator shows EGR codes...

[rickdlance]

4" exhaust threw no codes, but seamed down and power and hurt fuel mileage. Running both LLY's without cats and love it. Better sound, slightly better fuel mileage, and no codes.