LMBTom

Hi all,

I've got a strange issue that has developed sometime within the last few months. My stock muffler flaps/valves are not opening over 3500 rpm. They're not opening at any RPM.

They're not stuck as they open fine when I remove the dual-mode exhaust fuse. I actually drove the car around for the past month with the fuse out and the drone has finally got to me, so I put the fuse back in.

I don't have a m2w switch and the car has a stock tune (as far as I know).

And one additional thing that I don't think is related is that my mufflers rattle at idle sometimes - I think there's an internal baffle/piece loose that needs to be welded back.

From the symptoms, I believe that something is down between the computer and whatever controls the vacuum line pressure.

Any ideas?

Landru

I doubt it has anything to do with the computer, Tom.
There've been several reports of the flaps not working, and several causes.

For excample on the driver's side at the rear of the manifold there's a [green?] tube that'r reprted to work itself off. Don't think that's your issue though since removal of the fuse opened 'em.

Second thing I'd heard was a solenoid, behind the passenger's side tail light can go bad, also.

If you're still under warranty, of course Chevrolet should take care of finding & fixing the issue. Out of warranty's another matter.

Will BTTT your request in hopes those with more experience with this might see it & chime-in.

LMBTom

No warranty, so I'll be trying to work this out on my own. I'll see if I can locate that solenoid and test it out.

Landru

Be sure to check real careful, it's supposedly somewhat hidden under a flap & easily missed.
Going strictly from memory its behind the inner passenger's side rear light housing, [/u]below[/u] the light housing proper. The good news is if it is the solenoid, it isn't an expensive part.
(I'm somewhat susprised no one else has stepped-up to help a fellow Corvetter. Whatever. )

In any event, good luck.
You should be able to swing this if others here have, Tom.

Bill Dearborn

The solenoid can be reached by removing the passenger side inner taillight.

Do you have a DTC P166A? That can show up when the exhaust valves aren't working correctly.

Besides the solenoid there is an electronic control module located at the right rear of the trunk area under the carpet. It controls the solenoid.

Have you tried pulling the vacuum line off the left side exhaust valve yet? If so, did the right side valve open when you pulled that line. Both sides should open.

The fuse provides power to the control module so when you pulled it that removed all power to the module. That probably cut power to the solenoid which opened/closed (whichever) and cut off the vacuum to the valves. That action indicates there may be a good reason to look at the module at the right rear of the trunk compartment.

Bill

Hercules Rockefeller

not to go too far off topic, but if anyone knows how to get your car to do this *on purpose*, I'd love to hear it. Sometimes I need to keep the center pipes closed (to make sure I can pass sound at WOT at a few tracks here in CA).

haljensen

Something doesn't make sense.

How do you know that the valves aren't opening at 3500 RPM?

If you DO NOT have vacuum at the valves the valves are OPEN. Your statement of the valves not opening means that you DO HAVE vacuum.

Does the car start with the valves open and then close them within a few seconds? (Normal).

LMBTom

Once I figure out what is causing my issue, I'll let you know


The car is not very loud at high RPM's and I've had someone in the car revving the engine over 3500rpm while I was looking at the valves (not opening).

I do have vacuum. The problem is that the vacuum isn't going away over 3500rpm

Yes.


And I haven't made any progress yet. I'm working this weekend, but will get the back of my car apart as soon as I can

2k Cobra

Another test you can make is put car in "Competition Mode" and see if things work at 3K RPMs.

I would test the car driving it, not free revving the engine.

Best of luck, 2k

fisher auto

Drone? Not to steal the thread but I've got my fuse pulled and I think this thing is quite! I've had Bullets on my C5's now that's drone.

sysadlight

Were you able to resolve this issue? I've spent some time searching and have not found the right answer. I too am having some similar issues.

My issue:

I recently pulled an aftermarket exhaust, and re-installed a brand new NPP exhaust. The vacuum lines appear attached to the solenoids.

When car is off, valves are open. When car starts, valves close before I can get to back of the car. That would mean there is vacuum to the valves right?

When car is shut off, after 2-3 seconds they both slowly close.

I tried pulling the fuse, valves stay closed all the time with engine running.
I installed the M2W switch prior to pulling fuse and I can hear the M2W clicking and seems to work, but again valves stay closed still.

Hopefully someone can point me in right direction Maybe it is something simple?

Thanks
Mike

haljensen

I'm confused. Your second line says 'When car is off, valves are open".

Your third line says "when car is shut off ------they both slowly close".

Which is it?

sysadlight

Oops my bad...

I meant they both slowly open.

I also tried pulling one of the vacuum lines off the valve today and when I did they both snapped open.

So I have great vacuum pressure to keep them closed. Can't figure out why the vacuum source essentially wont stop the vacuum and allow them to open. With fuse pulled, still have strong vacuum holding them closed.

Appreciate any help or ideas before I have to have the dealer look at it.

Bill Dearborn

If you pull the fuse that kills the module that controls the vacuum solenoid. You say if you pull the fuse the vacuum is still present. However, try pulling the fuse and removing one of the hoses at the exhaust pipe. The valves should open, then after they open re-attach the hose and see if they close. If they close that means the solenoid is stuck in a position where it still supplies vacuum to the valves and will need to be replaced.

Not sure how anybody knows whether the exhaust opens at 3500 rpm anyways. A little difficult to see unless somebody is riding behind the car with some binoculars as they do not open under no load jazzing the engine in nuetral conditions. Here is the description from the SM:

Exhaust Tail Pipe Flow Control System Description and Operation
The Exhaust Flow Control (EFC) System enhances engine performance. The system has 2 modes of operation:
Normal

Competition

Normal Mode

When the vehicle is stationary with the engine running the exhaust flow control module (EFCM) commands the vacuum solenoid On, which supplies engine vacuum to both exhaust flow control valves. This causes the valves to close, diverting exhaust flow through a baffled path inside the mufflers. As vehicle speed increases, throttle position reaches 25 percent or greater and engine speed reaches 3500 RPM, the EFCM commands the vacuum solenoid off. This causes the valves to open, diverting exhaust flow through an un-baffled path inside the mufflers, thus enhancing engine performance.
Competition Mode

When traction control is driver disabled, vehicle speed increases, throttle position reaches 25 percent or greater and engine speed reaches 3000 RPM, the EFCM commands the vacuum solenoid off. This causes the valves to open; diverting exhaust flow through an un-baffled path inside the mufflers more frequently and at lower engine speeds.
The system also delays exhaust valve activity during wide-open throttle acceleration to inhibit exhaust valve actuation when the accelerator pedal is released and reapplied while shifting gears.
The EFCM has the ability to detect electrical malfunctions within the system. Any electrical malfunction detected will cause the system to be disabled and increased exhaust audibility.
The system uses the engine control module (ECM), body control module (BCM), electronic brake control module (EBCM), EFCM, exhaust flow control valve vacuum solenoid, vacuum reservoir, vacuum lines, 2 exhaust flow control valves and the serial data circuit to perform the system functions.

Here is the vacuum schematic for the exhaust valves:




(1) Exhaust Tail Pipe Flow Control Vacuum Check Valve and Hose
(2) Exhaust Tail Pipe Flow Valve Vacuum Pipe - Chassis Front
(3) Exhaust Tail Pipe Flow Valve Vacuum Pipe - Chassis Rear
(4) Exhaust Tail Pipe Flow Valve Vacuum Pipe - Valve Solenoid to Control Valves
(5) Exhaust Tail Pipe Flow Vacuum Valve Solenoid
(5) Exhaust Tail Pipe Flow Valve Vacuum Pipe - Vacuum Valve Solenoid to Reservoir Tank
(6) Exhaust Tail Pipe Flow Valve Vacuum Pipe Reservoir Tank
(7) Exhaust Tail Pipe Flow Valve - Right
(8) Exhaust Tail Pipe Flow Valve - Left

Here is the electrical schematic:




Bill

sysadlight

Bill,

Thats correct. Regardless of fuse pulled, vacuum still supplied to exhaust valves, keeping them open.

Looks like it's a $20 part, but the difficulty of reaching and replacing it myself looks to be a dealer warranty fix. Dropping it off Wed. Will update with the outcome...

haljensen

You need to re-phrase your first sentence.

NO VACUUM means OPEN valves. (Car is off, sitting in the driveway)

VACUUM means CLOSED valves. (Car is running but below 3500 RPM or or the fuse is pulled or the aftermarket exhaust control switch is activated).

sysadlight

Man I really should proof my posts before submitting!

You are correct. My issue is that I cannot kill the vacuum at all, pulling fuse does nothing. When engine is running, vacuum keeps valves closed all the time.

If engine is turned off, valves slowly open and stay that way.

If, while engine is running, regardless if fuse is pulled or not, I pull one of the rubber hoses off either of the exhaust valves, they both snap open. I can feel the pull of the vacuum on my finger.

Car goes in Wed. Will update this with the resolution.

Thanks all for posting and getting me straight

dmuellenberg

Still not correct - should be:

NO VACUUM means OPEN valves. (Car is off, sitting in the driveway or the fuse is pulled or the aftermarket exhaust control switch is activated)

VACUUM means CLOSED valves. (Car is running but below 3500 RPM).

sysadlight

Thats my problem...
or the fuse is pulled or the aftermarket exhaust control switch is activated)

This does nothing while car is running. Pull fuse, valves stay closed due to vacuum still holding them shut.

dmuellenberg

Yes, I do understand your problem. I was just stating what should normally happen under those conditions when everything is working properly. The previous poster had stated that the the valves should be closed with the fuse pulled or aftermarket switch is activated, which is incorrect, they should be open. Sounds to me like you have a solenoid problem.