Struggling with exhaust issue

[jethrobandit]

About a year ago I hit something metal in the road and thankfully the damage was only to the bend in the passenger side pipe after the HFC. It was early in my drive home from TX, so I had to continue to drive and then had to for another couple of weeks before fully fixing.

Sound hasn't been right since then; more hesitation in the midrange; sounds extra muffled. I had a shop cut out that section and weld in a replacement. I have dual-mode exhaust which I love the sound of. However, I'm thinking they must have done a really poor welding job as I think there is quite a bit of rough slag on the interior welds?

I've done a bunch of testing, trial and error fixes, and looking at other issues. I'm thinking maybe its not flowing freely, more backpressure, not scavenging properly? I've changed spark plugs, air filter, new mass airflow sensor, cleaned throttle body... nothing on that end has made a difference. Maybe my entire exhaust is now crapped out?

Think I can get a shop to replace catback through x-pipe and still keep dual-mode? Or likely have to replace whole system? After that I have to fix my new mysterious drop in oil pressure when warm.

[0stones0]

Any way to get a camera at the inside the weld area, to see how much “slag” might be there?

[TheBrightSide]

How many miles are you at? Sometimes the oil pump pickup gaskets need to be replaced… I’m not sure if an exhaust would get THAT restrictive, that it would work against the engine that much. Even in that case, it would mean that the oil pressure would raise/increase, no decrease, no..?

If you want to check the exhaust system flow/operation, you can pull the fuse on the NPP exhaust system, which will leave the valves fully open. At that point, it should be a fully flowing catback exhaust system. I would probably start checking other things regarding engine oil pressure, as it could be something internal (ex: oil bypass valve, “dog bone”)…

I have a leaking oil pan gasket, and I’m currently at around ~48k miles right now. I plan on re-using the stock oil pump, but I will be getting rid of the factory plastic/composite(?) oil bypass “dog bone” valve, and then installing a billet one, with fresh new o-rings. Same thing goes with replacing the oil pump pickup tube o-rings, since they can degrade over time I will also be installing a pickup tube brace as well, while I’m in there..

People also say to avoid running a high pressure engine oil pump, if you’re running a “basic” NA engine setup. I would also trust my stock, factory OEM oil pump, rather than some random one. I do, however, trust most Melling engine oil pumps for GM LS V8 engines though.

[InFiD3ViL]

While you are in there I would suggest replacing the camshaft retainer plate. It has an o-ring type seal that can also cause oil pressure issues, as it flattens out over time. Its like $25 for the GM one.

[CamaroCracka]

The stock 2.5" exhaust is plenty for the LS3. A little bit of welding slag is not going to affect it. I would be looking for an obstruction, like the internal tubing on the muffler broke or a something clogging the cat. I would also look at the header gasket as small leak created by the hit on the exhaust could affect performance.

Are you only noticing the difference when the NPP should be kicking in, i.e. is the dual mode working. IIRC, they operate off of vacuum and should be open when the car is shut off. As was mentioned a cheap borescope might be a good investment.

[mr_honez]

Originally Posted by CamaroCracka

The stock 2.5" exhaust is plenty for the LS3. A little bit of welding slag is not going to affect it. I would be looking for an obstruction, like the internal tubing on the muffler broke or a something clogging the cat. I would also look at the header gasket as small leak created by the hit on the exhaust could affect performance.

Are you only noticing the difference when the NPP should be kicking in, i.e. is the dual mode working. IIRC, they operate off of vacuum and should be open when the car is shut off. As was mentioned a cheap borescope might be a good investment.

Along the lines posted above If you hit something hard enough you can break the ceramic material inside the cat causing a blockage. It has happened to me on a different vehicle and I had to replace the cat

[gtstorey]

Not really possible to have enough slag on the weld that it will change the sound. Start looking elsewhere.

[morepowerjoe]

Originally Posted by TheBrightSide

How many miles are you at? Sometimes the oil pump pickup gaskets need to be replaced… I’m not sure if an exhaust would get THAT restrictive, that it would work against the engine that much. Even in that case, it would mean that the oil pressure would raise/increase, no decrease, no..?

If you want to check the exhaust system flow/operation, you can pull the fuse on the NPP exhaust system, which will leave the valves fully open. At that point, it should be a fully flowing catback exhaust system. I would probably start checking other things regarding engine oil pressure, as it could be something internal (ex: oil bypass valve, “dog bone”)…

I have a leaking oil pan gasket, and I’m currently at around ~48k miles right now. I plan on re-using the stock oil pump, but I will be getting rid of the factory plastic/composite(?) oil bypass “dog bone” valve, and then installing a billet one, with fresh new o-rings. Same thing goes with replacing the oil pump pickup tube o-rings, since they can degrade over time I will also be installing a pickup tube brace as well, while I’m in there..

People also say to avoid running a high pressure engine oil pump, if you’re running a “basic” NA engine setup. I would also trust my stock, factory OEM oil pump, rather than some random one. I do, however, trust most Melling engine oil pumps for GM LS V8 engines though.

What does the pick up o-ring have to due with his exhaust? The oil pressure has nothing to do with how the engine runs.

[TheBrightSide]

Originally Posted by morepowerjoe

What does the pick up o-ring have to due with his exhaust? The oil pressure has nothing to do with how the engine runs.

Highly doubt it’s an issue with the exhaust, unless the cats got clogged; which again, you would know (ex: lack of power). Same thing goes for cracked cats, especially when they start coming apart and jamming in the exhaust pipes. Your car/engine would run like crap, and that would still have nothing to do with oil pressure issues, which are INTERNAL (to the engine itself). And as far as the NPP valves, there’s people who run turbo chambered mufflers, with absolutely no issues; so those single valves on a QUAD exit exhaust would certainly not be an issue.

Try installing an oil pump pickup without a good o-ring, or drive an engine with a badly failing one… In the case that you do manage to drive on an engine with a partially degraded oil pump pickup o-ring seal, you’d maybe get away with it for a bit if you’re lucky, but certainly not forever. It most certainly affects oil pressure.

If it was an issue where the oil pressure gauge didn’t work at all, you could potentially replace the oil pressure sensor, as a means of process of elimination. But regardless, like others had mentioned, there’s other stuff you’d want to check and replace while you’re going through all of that engine stuff, regarding oil pressure anyways.