Ericbariello

Hi there. I am German, lived & worked in the US long time ago. Since then I love the Corvette. Today I am driving a C6 LS3 Z51 US-Model (2008) with the Original Exhaust. I don’t have much time to drive the car (25000 miles in total), it’s almost new looking, parked in a Garage. I love it but we use it mainly for holidays (driving through Switzerland, Italy and France


Probs: So, since 3 months I got a frequently upcoming problem. The exhaust with sound control and twin tailpipes with flaps/valves stays open after some time (after the exhaust got hot maybe). The same sound as if I remove the fuse. If I take out the fuse and reinsert it, the louder sound is gone. But after some time, the flaps again stay open. The German dealers have no idea, the electronic diagnostic system shows no errors. I already exchanged the fuse but still, after some time the flaps stay open. I only found other opinions regarding the Z06 but not for the regular C6. All regarding actuators vacuum and line.


Maybe there is a simple way to go through. Could you please help me with a simple checklist? Am I able to solve the problem easily or describe it to a German dealer? Does anybody has the 3,5 pages from the service manual to show to the dealer. Thanks a lot.

Dano523

There is a vacuum port off the back of the intake manifold.
This port gets a tube, the tube goes 12V pneumatic solenoid, then tube out the pneumatic solenoid to the back of the car where it connects to a vacuum reserve ball and T's out to the two muffler pneumatic solenoids to control the gates.


Now the electronics part works on the system, once the engine has come up to the specific RPM, the BCM will kill the power to the 12V pneumatic solenoid in the engine bay to stop the vacuum out of it to the mufflers.

So the fact that pulling the fuse and plugging it back in will close the NPP gates, means that the problem is in the electrical side of the math, and not a vaccum leak problem instead.

Here, I would first check the NPP 12V pneumatic solenoid in the engine compartment to make sure that is not going out, and if it still good and does not have a wiring problem back to the BCM, then would focus on the BCM next.



On the BCM, it can have a few problems, and the big one is if the AC box drain becomes plugged, which allows the AC box to fill up with water, and drain down into the BCM instead.

Normal SOP for a problem with a BCM is to just replace it at the dealer level, but when this does not become a option, pulling the BCM apart so it can be cleaned/connectors check is tangible instead.



Hence it could be something as simple as just corrosion on the tabs that make contact to the fuse spades, and by just cleaning any corrosion off them/their connector points to the board, could easily solve the problem without having to replace the entire BCM instead.

Ericbariello

Great, that's a new point to check. Thanks!

Ericbariello

Hi, me again. It’s just the same problem, sometimes and only if the engine is hot, the exhaust flaps stay open. To find out, if it’s a mechanic or an electronic problem, I started the following test:


Cold condition, engine start, flaps closed, I remove the fuse, flaps open (I can do this several times with the same effect as it should be),
Hot engine, the flaps stay open after accelerate once above 3000 rpm, then they stay open even after stopping the car. If I remove the fuse while the c6 stays and put it in again, they flaps close (now it’s the same effect as above).


I think, it’s an electronic problem - what are you guys thinking? If you agree, which part (senor, relay, etc) has to be removed? Thanks a lot!

Btw Dano, the AC box almost looks new.

AORoads

It MAY be an electrical vs. a mechanical (vacuum to the NPP exhaust) problem, but just to reiterate what "Dano" said: "...On the BCM, it can have a few problems, and the big one is if the AC box drain becomes plugged, which allows the AC box to fill up with water, and drain down into the BCM instead. ..."

The AC box can LOOK good, but the drain line/hose can become plugged. It has nothing to do with how good the box looks; it's all about the drain line.

On the NPP exhaust, when the engine is off, the "flaps" are open; it takes engine vacuum to hold the flaps closed. That's why on start up, the sound is loud (open flaps) and then it quiets down as the flaps get closed by engine vacuum.

I would have thought your problem is vacuum (mechanical) rather than electrical, but I'm not that good at electrical. It appears to me that your car loses vacuum to the flaps which then allows them to stay open while you are running. I guess it could be either electrical or mechanical, or a combination of both.

If your dealership has access to the Factory Service Manuals (also called the Helms Manuals for the company that makes them), they should be able to diagnose the problem. Here's a thread about it: https://www.corvetteforum.com/forums...aid-149-a.html

Dano523

The NPP 12V pneumatic solenoid is normally closed, meaning that the npp system has to send voltage to it to allow it to open, so the vacuum from the intake manifold can pass through it to close the muffler gates.

So, either there is a leak in the vacuum lines that is happening when the motor gets hot, the NPP 12V pneumatic solenoid is having problems and when it get hot, is not opening up, or the NPP system is having problem with sending power to the NPP 12V pneumatic solenoid to hold it open instead.

Hell, it could be as simple as just the ground wire on the NPP 12V pneumatic solenoid is spotty, and the problem itself.

So, the NPP 12V pneumatic solenoid is located inside the rear bumper cover just below the inner passenger side tail light, and the easy check is to just check the connector to make sure that it getting 12 volts through it to being with (to open the valve). If you don't get 12 volt the connector pins with the car idling, then double check the ground wire on the connector to make sure it not the problem.

If you have 12 volts on the connector, then the NPP controller module is fine, and you either have a bad NPP 12V pneumatic solenoid, or the leak in the vacuum line instead that is controlling.

Ericbariello

You both are great , thank you very much. I have to "translate" (think over). What keeps me crazy is, that is's only coming up it the engine is hot and once above 3000 rpm (and then stays open in every rpm range) ..

Biggarlick

I am having the same problem with my 2008 Coupe. Have you had the problem corrected and if so, what was done?