Hi all-

Okay got a 'new to me' 2008 coupe with npp - excepting it doesn't work.

I troubleshot the rear end and I know that everything is good from solenoid to actuators.

Went to the front and got on the vacuum line before the check valve so I had a straight shot to the intake manifold. used a borescope and I know the hose is connected and no kinks so I hooked up my vacuum gauge and the vacuum very slowly rose to 15" and then stopped. Hmm - not enough

Shut off engine and lo and behold I could pull a vacuum to about 25 inches where I stopped. Which means I hope there is something blocking either the port or the hose.

So my question is - is there any check valve or anything on the port itself that could cause this? From my reading and the service manual I presume it is an open port given that there is a check valve before the quick disconnect.

Next step is to pull hose off port and check vacuum directly - if it is good fine but what if no? The engine runs fine now. The intake manifold is just a big tube with no moving parts (correct?) so if it is plugged I am reluctant to blow air to clear it as who knows if it is a bug or something that I really don't want the engine to eat.

Doesn't look like a huge job to pull the intake (other than new gasket set) in one piece with no disassembly to check it out but i would rather not do that.

Advice? Comments? Thanks!

Jim

 

Did you check the fuse yet?

 

Yes - the fuse is what got me on the trail to begin with. i tried to install a mid2wild and it didnt work.

When I checked the rear system i pulled a vacuum with a mighty vac and the system works fine which means the fuse, efcm module and solenoid are fine. Not an electical problem

So I have two problems - why am i not getting vacuum off the front intake port. Which i hope is just the hose. Trying to make sure I dont bust anything if it is not the hose.

i think their is a leak on the two sections that run along the frame but i will deal with that later.

 

So what's the problem? It sounds like the flaps are stuck open (loud mode) all the time, correct? That's what would happen if you don't have vacuum going to them.

A stock LS3 probably won't have much more than 15 inches of vacuum at idle -- maybe 16 or 17. Either way, it's plenty to actuate an NPP system. My cammed LS3 only makes between 12-15 inches most of the time, and I can operate my B&B Fusions whenever I want.

So if you T into the vacuum line where it connects to the vacuum actuators, and run the engine at idle, you get 15 inches? What happens if you bring the revs up to where the system should be switched to "loud" mode? All vacuum should be released from the system.

I'm also not 100% sure, but the factory NPP system might have a vacuum canister as well. Something to check. I'd also pull the vacuum line directly off the back of the manifold and take a reading there.

 

So you hooked a vacuum pump to one of the rear vacuum lines and it held 25 inches with the engine off? As far as I know, that would be normal since there is a 1-way valve in the system. I have my valve mounted directly behind my intake manifold, and if I close the flaps and turn the engine off, the system will hold vacuum for a week or more. That's what the valve is meant to do.

I don't know if the factory NPP system uses a solenoid valve that is powered-open or powered-closed, though. My aftermarket solenoid valve from B&B is sprung-open when power is lost.

 

i hooked up a mightyvac to the rear forward of the solenoid and i could get the flaps to close with the engine running so basically all the electronics work fine. mine stay open all the time i am not getting vacuum to the solenoid in-port it appears.

When i ran the diagnostic sequence in the service manual it says to check the vacuum reading at the quick connect in the front. I couldnt get any vacuum there so to eliminate the check valve that sits between the engine vacuum line and the quick connect I broke the line so that it was a straight shot from the intake port next to the booster port on the intake to the vacuum gauge.

When i started the engine the gauge crept up to about 15" really slowly - snails pace which i did not expect for a 12 line between the port and the gauge. took about 30 seconds to get to 15-16

I shut off the engine leaving the gauge attached to the line to the intake port, dumped the vacuum and - this is what caught my eye - I could pull and hold 25 inches of vacuum and I expected to not be able to pull any vacuum. So either I have one of the tightest engines in the world or something is plugging the line. After I dumped the vacuum again I restarted the engine and I got Zero, nada vacuum from the running engine. So there appears to be a restriction somewhere.

Again this is a straight shot through 12 inches of vac hose to the gauge. I did not have time to go any further - so the next step from SM is to pull the hose off the intake port and attach gauge there directly.

that is a pain in the hand for sure that is a really tight space. so if i find it is the hose i can replace that ez enough but what bothered me is the 'blocked' line effect i got pulling the vacuum the 'wrong way'- so my question is if anyone knows if there is any valve mechanism in the port itself that could close and cause the system to hold vacuum. there is no mention of that in any descriptions i can find. if there is another check valve in the port itself that would explain why i could get a vacuum and hold it going the 'wrong way.'

thanks for the info on the vacuum you have seen at idle. the SM says i should see like 16-30 and i know that it takes about 20 on my car to close the dampers - and they are supposed to be closed at start, etc.

i love the sound with the dampers open but the drone at cruise rpm is annoying as hell - that is why i got the mild2wild so i could have it both ways

 

There isn't anything built into the manifold that would cause a restriction -- it's just a small plastic nipple that the vacuum hose plugs into.

Is the engine totally stock? I know some of the FAST manifolds need to have that port drilled out during install. Or maybe yours is blocked. It's not that hard to get to the line on the rear of the manifold. A little tight, but can be done.

 

Thanks for the second reply - and thanks for the scoop on the real life vacuum. I replaced the line from the intake to the front chassis line and got the 17" so your previous post was spot on.

And you are right it is a tight fit and I have the scratches to prove it LOL - found out that using the right hand actually worked better than the left.

Turned out the problem was with the rubber fitting that hooks up to the vacuum line - the one that points forward rather than to the left.

Thanks for the help - I am going to do another post on this thread with what I learned on this.

 

I spent a good bit of time troubleshooting my NPP which would not close. I found this problem while trying to install a M2W switch.

The GM Service Manual troubleshooting is very lengthy so after so thought this might help -- first of course check the fuse - lowest right most on fuse panel.

This whole procedure works best if car is elevated - I backed mine up on ramps

1. Go to the rear of the car - find the quick disconnect that goes to front of car and check vacuum there - if vacuum then you have just checked 50% of the tubing.

2. If no vacuum go to front and disconnect the quick connect there if you have 15+ in. of vacuum then your problem is in the front or rear chassis line. Hard to find line routing and disconnect without a lift.

3. If you had vacuum at the rear in #1 - remove both right tail light lenses - SM says inner but both gives you way more room.

4. You will find the solenoid under a rubber protective flap. Check to make sure electrical connect is good.

5. There are two branches off the solenoid - the one that goes left goes to the valves on the actuators. The one that points front is the vacuum supply.

6. Remove supply and hook MightyVac there. Start car and pull vacuum. If the valves close then you have checked the tubing and the exhaust controller and solenoid both since the default is to close the valves.

7. If valves don't close put mightyvac on other tubing from solenoid and test - if they close then tubing and actuators are good. If not test each actuator and tubing individually for leakage - also look real closely at the rubber connectors.

8. if they close then reattach everything and go to the triple line with the quick disconnect try and pull a vacuum there. If it will not hold then closely check line and attach mighty mac to reservoir and test for leakage.

At that point you have tested all the vacuum which leaves the solenoid or the exhaust controller as the probable culprits - that is beyond my ability to test without OBDII to command the controller and solenoid. If you have that capbility then have at it - OTW I guess a trip to your 'favorite' dealer service department is in order.

Hope this helps - OBTW thanks again to everyone who replied and my M2W works perfectly so I now have best of both worlds.

Keep waving!

Jim

 

I will be trying to fix mine next weekend. I can't stand when something isn't working the way it should