Loud exhaust noise on startup
2008 GMC Envoy is only equipped with one of two engines:
4.2L (254") 6-Cylinder SFI
5.3L (325") V-8 SFI
Niether of these engines are equipped with an EGR valve, so I guess the probability of that being the cause of your noise is pretty much zero to none.
If you believe the noise is being caused by the exhaust ststem, then the only way to verify that is to inspect the exhaust system. Leaks are easier to verify with the engine running.
With that said, there is also a Technical Service Bulletin (TSB) that is published by GM that addresses customer complaints about loud noise that is being caused by the electro-viscous engine cooling fan clutch. Some people describe it as exhaust noise and others describe it as the engine "racing" or "roaring".(even though the tachometer (if equipped) will be reading normal)
It basicly says that it can make noise on startup due to high rpm of the fan which goes away once the electric solenoids open and allow the fan to start free-wheeling. GM says this is normal operation. You might want to check to be sure this is not what you are hearing. (it can be pretty loud)
May 26, 2012 |
2008 GMC Envoy