2009 NPP Issue Help Needed
Thread Starter
Heel & Toe
Joined: Apr 2008
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2009 NPP Exhaust Issue. Help Needed
Hi back again after a 14 year hiatus from vettes. Learned a lot here before and about to beat on a dead horse. I've tried to find information about this but seems nothing really works so please bear with me.
The valves on my exhaust are not closing on start up for quiet mode. I've checked the fuse, and it's in place. I want to install the control but seems to be moot if they aren't actuating at all. I really would like this thing to tone down while cruising because it's irritating with my tinnitus. Any ideas as to how this thing is routed and controlled would be greatly appreciated.
Glad to finally have another and the LS3 is perfect. TIA
The valves on my exhaust are not closing on start up for quiet mode. I've checked the fuse, and it's in place. I want to install the control but seems to be moot if they aren't actuating at all. I really would like this thing to tone down while cruising because it's irritating with my tinnitus. Any ideas as to how this thing is routed and controlled would be greatly appreciated.
Glad to finally have another and the LS3 is perfect. TIA
Last edited by meltblown; Feb 6, 2024 at 07:52 PM.
Race Director
Joined: Jul 2005
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From: Central MO
There's a solenoid that fails that's located somewhere inside the bulkhead by the passenger side tail lights, or possibly underneath the car behind the lower valance.
I can't tell you exactly where it's at because my car didn't have NPP from the factory. I retrofitted it and added NPP In a Box. Hopefully someone who knows will be along shortly.
I can't tell you exactly where it's at because my car didn't have NPP from the factory. I retrofitted it and added NPP In a Box. Hopefully someone who knows will be along shortly.
Last edited by BadAV; Feb 7, 2024 at 05:10 PM.
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The solenoid is the most likely cause of the problem. But in my case it was a failed vaccum acctuator on the muffler it self. It was leaking vaccum so that neither valve would close. I plugged the line to one side and the other side closed. I was able to find a used replacement and have been good since.
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One simple thing you could try: take the hoses off the solenoid and join them together with a short coupler. If there are no vacuum leaks causing the problem then the butterflies should close soon after the car starts and stay closed. There may be a check valve at the head of the vacuum line, can’t remember, but the butterflies should stay closed except maybe when you put you foot into it and manifold vacuum drops. If there is a check valve, the butterflies will probably just stay closed. If this proves out, then the problem is most likely with the solenoid or much less likely with the exhaust control module.
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Sorry, but that’s exactly opposite to what the OP wants. Pulling the fuse pretty much guarantees that the butterflies stay open all the time if the solenoid is working correctly. The OP wants the OEM method of operation where the butterflies close when the engine starts and stay closed except under the programmed rpm and throttle parameters. And if the solenoid is fused either open or shut, pulling the fuse won’t affect anything in how it is currently operating. Same is true if there is a vacuum leak or the exhaust control module has failed.
Thread Starter
Heel & Toe
Joined: Apr 2008
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You guys are great. It was a PITA to get the solenoid out but done. Jumpered the vac lines together and the valves close. Getting 14V at the connector. New solenoid arriving tomorrow. Now will install the kit to control it. Thank you
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Should have done clay bar, paint correction, and ceramic coating. I'm going to do mine after I get the 4LT leather dash reglued.
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Heel & Toe
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