Exhaust Flapper Noise - Will it go away eventually?

hirdlej · April 26, 2016

Hi guys, I have a 2015 Silverado RCSB with the 5.3L. When I cruise through town at 25-35 mph I use the lightest of foot. When I just barely touch the gas pedal to obtain the best mileage possible the exhaust starts grumbling at me. I suspect this is the flapper valve. I am tempted to just wire it open and call it a day, however I love how quiet this truck is otherwise. With that being said, will the spring soften up a bit so the valve isn't constantly chattering and trying to slam shut with low exhaust flow? Does anyone have any experience with these things breaking in? If they don't break in, does GM have an updated flapper valve yet or are guys just wiring these open?

newdude · April 26, 2016

I'd stick a bolt in it and keep it open.

fondupot · April 26, 2016

The truck will still be pretty quiet with the flapper open. Just clamp it open and call it a day.

hirdlej · April 26, 2016

That's pretty much what I figured you guys would say. I'll just do that then. It's probably not worth the hassle of GM putting another system in just for it to continue to happen. I have a race truck if I want to go fast. I'm just enjoying how whisper quiet this thing is for daily driving. The ecotec 5.3l goes pretty good in this truck as well. I did some freeway pulls in 4th gear, rolling into the gas so it wouldn't downshift. You can really feel the VVT kick in around 4500 rpm or so, then it feels like the truck gets another set of lungs and before I knew it I was knocking on 100mph. All whilst not really hearing any V8 roar. It's kind of fun that way. Right now my gas mileage is shit since I'm going through my break-in period. I'm going to change the oil here now that I have 1k miles on the odometer and start driving it more *normal*.

TJay74 · April 26, 2016

The flapper is hard welded into the system so only way dealer can change it out is to replace the entire system. Also the LTx engines do not use any type of VVT system. All they have is AFM which only activates under light throttle inputs, anything more than about 6%-10% throttle and it will kick the system out of AFM mode.

hirdlej · April 26, 2016

I'm almost certain the 5.3L has VVT. If not, then this article is wrong: http://media.chevrolet.com/media/us/en/chevrolet/news.detail.html/content/Pages/news/us/en/2014/Nov/1117-silverado.html

I have been using a range AFM disabler since day #1. I'm not a believer in letting 4 of my 8 pistons moving without pressure on the rings from combustion. It's been a trouble-free device and boy are these engines smooth.

emeryz28 · April 26, 2016

I have my flapper clamped open. I noticed it made the truck a little louder, but now I am so used to I almost forget its clamped. I do enjoy that the metal clank sound on starup is gone.

newdude · April 26, 2016

The flapper is hard welded into the system so only way dealer can change it out is to replace the entire system. Also the LTx engines do not use any type of VVT system. All they have is AFM which only activates under light throttle inputs, anything more than about 6%-10% throttle and it will kick the system out of AFM mode.

They have VVT, AFM, and DI. VVT has been in GM small blocks since 2007.

AFM runs under the following conditions:

Engine has been running for greater than 30 s

Engine speed is between 700 and 2800 rpm
Engine oil pressure is between 187–455 kPa (27–66 psi)
Engine coolant temperature is between 40–129°C (100–264°F)
Engine oil temperature is between 16–128°C (61–263°F)
Throttle angle is 6% or less
Ignition voltage is greater than 11 V
Transmission is not in first, second, or reverse gear
Vehicle speed is greater than 25 kph (15.5 mph)
Brake booster pressure is greater than 42.0 kPa (6 psi)
Vehicle is not in fuel shut of mode
Vehicle is not in heater performance mode
Vehicle is not in tip in bump acceleration mode
Vehicle is not in oil aeration mode
Vehicle is not in low range (if equipped)

headpan · May 3, 2016

ok cool

this is obviouslly the sound im hearing

how do i wire it open?

where is it located

thanks

HoosierZ · May 3, 2016

It's located right behind the muffler. Look for 2 square pieces with a spring between them. Twist the outer piece 1/4" turn and lock it open with a small bolt, wire, hoseclamp, nail, etc. I bolted mine open and now it has a deep, throaty sound when I start it but I hardly notice it any other time.

glcbn · May 3, 2016

Very easy to do.

headpan · May 4, 2016

is this flapper controlled by engine management system? ya know eletriclly

SkiDooNick700 · May 4, 2016

is this flapper controlled by engine management system? ya know eletriclly

No, thats one of the reasons you can just clamp it open and not worry about some electronic motor burning up. It's purely on pressure thru the exhaust as far as I know.

glcbn · May 4, 2016

No, thats one of the reasons you can just clamp it open and not worry about some electronic motor burning up. It's purely on pressure thru the exhaust as far as I know.

^^^^ This