I am getting a check engine light saying Catalytic thermal efficiency below threshold, bank 1 and 2. I just replaced the stock muffler (which had grenaded itself due to a broken timing change) with a Thrush Red Hot, using stock tailpipe. Could this be the problem and how do I correct it?

 

Would help a lot if we knew the year, model and engine size.
Different years and models have different amounts of components and engine sizes.
At this point we don't know if it has more than one converter or possibly 4 oxygen sensors. Did you get that dreaded P0420 code? If so there are a few reasons it can come up along with the check engine light. Has the exhaust system been altered?
Did the engine misfire for a period of time where it might have melted the substrate in the converter(s)? After we can obtain some addl info may be able to provide some answer to your questions.

 

Sorry, can't believe I did that. 2008 F 350 XL 5.4, at, 2wd. Engine rebuilt and code came up on first test drive. Cleared several times and it returns. While trying to crank the truck with a broken phaser and cam gear, I grenaded the muffler. I could not find an OEM replacement and replaced with a Thrush Mad Hot of the same design. A Thrush rep told me reduced backpressure would not cause the code but an exhaust leak would. Not logical to me but there you have it. Thanks!

 

Remember the after cat sensors are actually monitors. They measure the 'absense" of oxygen ,or, how efficient the cats are . Unlike pre cat where the 02s are cross counting mixture values.. If you have access to a scan tool that can enter the PIDs you can see/watch the 02s and monitors to see what they are reading as far as values and activity. Muffler shouldn't affect monitor values unless the down pipe was polluted with air.

 

Thanks, but that is a little over my head. I am here because there aren't any trustworthy garages in my area, especially the dealers. I will try to see if I can just pay for a diagnosis.

 

Codes were both 420 and 430?

How does it run with the new chain? If the muff is a possibility, could restrict the flow a tad and see if the DTC stays cleared..

Possible causes..

Use of leaded fuel
• Damaged heated oxygen sensor (HO2S)
• Out of range engine coolant temperature (ECT) sensor
• High fuel pressure
• Damaged exhaust manifold
• Damaged catalytic converter
• Oil contamination
• Cylinder misfiring
• Downstream HO2S wires incorrectly connected
• Damaged exhaust system pipe
• Damaged muffler/tailpipe assembly
• Retarded spark timing
• Leaking fuel injector
Diagnostic Aids: The signal line lengths of the downstream

 

I think the code was 421, will have to check again tomorrow. Remember, I blew up the old muffler so I could have damaged a sensor. I installed a newly rebuilt engine and it runs great now, although the low end seems a little weak for this size engine. But with a heavy foot it does take off.