After replacing the catalytic converter with an aftermarket replacement, it is loud and runs rough?

Tiny
MALINA7
  • MEMBER
  • 2005 HONDA ACCORD
  • 2.4L
  • 4 CYL
  • AUTOMATIC
  • 209,275 MILES
So, I got this car, and the catalytic converter was cut off. So, I replaced it with an aftermarket one. I also had to replace the flex pipe and the long exhaust pipe with the resonator and muffler. I replaced gaskets and only 1 o2 sensor (downstream). It is still loud and runs like garbage. I need to know any advice you might have when working in this specific area. Please and thank you.
Thursday, February 15th, 2024 AT 4:31 AM

3 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,077 POSTS
Hi,

Can you tell roughly where the loud exhaust is coming from? It could be related the exhaust manifold or perhaps the aftermarket converter isn't fully sealed.

Also, there are two oxygen sensors (see pic 2 below). Are both installed? Also, in pic 1 I circled where the down pipe attaches to the exhaust manifold. There is a donut gasket that goes at that connection. Was it replaced?

Let me know.

Joe

See pics below.
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Thursday, February 15th, 2024 AT 8:09 PM
Tiny
MALINA7
  • MEMBER
  • 22 POSTS
The sound, I believe, is coming from the flex pipe and the back of the cat. The upstream sensor needs to be replaced but the downstream is brand new, but somehow got stripped. Yes, the donut gasket got replaced, but it wasn't snug. I don't think the spring Bolts were torqued properly. And 2 Bolts at the back of the cat are stripped so it's not tightened as it should be.
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Friday, February 16th, 2024 AT 11:55 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,077 POSTS
Hi,

That would explain the noise. The bolts at the back of the converter that are stripped, drill out the threaded end and simply install a nut and a bolt. If the oxygen sensor is stripped as well, that is going to cause another leak, but that may require a different repair. Am I correct the threads on the exhaust portion are what stripped?

The spring bolts need to be tight as well. Are you able to access them to tighten them? We need to eliminate all the leaks because they are likely causing the rough idle. The oxygen sensors are likely showing a lean condition due to leaks. As a result, the computer is trying to compensate by adding fuel.

Let me know.

Joe
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Saturday, February 17th, 2024 AT 6:25 PM

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