Australian here. I have a car problem that has plagued me for nearly two years and I’m still no closer to a solution.
All Wheel Drive (not front wheel drive)
Aftermarket headers make a hissing sound when installed. Not a constant hissing sound though.
If I’m in neutral the hissing sound is heard after you rev the engine - bring revs up to say 3000, then close the throttle and you hear a hissing/rattle sound as the revs return to idle.
No leaks heard at idle.
When you’re driving the sound is heard on acceleration - VERY LOUDLY. Same sort of sound - loud hissing. Not a ticking sound like you might expect from a manifold gasket though. This sounds like a dead flange gasket when accelerating under load.
If I accelerate very, very, very slowly there is no unusual exhaust sounds.
This might sound simple enough, but let me walk you through why I am confused.
On first install of Brand X headers I get this noise. So, I assume I have installed correctly and attempt to eliminate possible leaks before reinstalling them… the list of things I have tried is as follows;
- completely remove the EGR system. Still leaks.
- Reinstall EGR system. Still leaks.
- REPLACE the entire EGR system. Still leaks.
- Replace the cat converter. Still leaks.
- replace the ENTIRE exhaust system, cat back. Still leaks.
- Replace ALL engine mounts. Still leaks.
- try three different brands of gaskets. Still leaks.
- try three different brands of gaskets with a sealant. Still leaks.
- try Remflex gaskets. Still leaks.
- Pressure test each individual section of the Brand X headers. No leaks found.
- straight edge the manifolds and cylinder heads. All within tolerance.
- manifold studs checked and within tolerance (not stretched).
- Have the Brand X headers ceramic coated. Still leaks.
- give up and have an exhaust shop fit the headers. Still leaks
- give up again and have a second exhaust shop fit the headers. Still leaks.
- give up on Brand X headers and try Brand Z headers. Still leaks.
- install stock headers. No leaks.
Brand Z headers make the EXACT same hissing sound at idle (revs up, close throttle / hissing sound) as the Brand X headers. But, the acceleration noise is slightly quieter , or lower pitched, on acceleration with the Brand Z headers.
- both exhaust shops acknowledge the existence of the hissing sound. Both claim to be able to eliminate the sound. After installation the first exhaust shop denies the existence of the hissing sound, despite is still being audible.
Second exhaust shop, after installation, tells me the hissing sound is “normal”.
Third exhaust shop - yes, there was a third - says he cannot find the leak, and to bring the car back when it gets worse.
Both Brand X and Brand Z headers have two flex joints in the Y-piece. On both Brand Z and Brand X headers I had both these flex joints replaced. With Brand X I had a whole new Y-piece sent. None of this fixed the hissing sound or loud acceleration noise.
There are no heat shields on either Brand X or Z headers.
The engines compression test results are 180psi over all six cylinders with a deviation of plus/minus 5psi.
There are no other modifications to the engine of drivetrain.
I have also tried two different brands of airfilter, as well as replacing the two accessory drive belts. And, I’ve inspected the timing belt - replaced the hydraulic tensioner - and there are no abnormalities. No wear marks of the inside of the timing covers.
No wear marks on the engine bay from clashing headers.
No soot marks around any flanges or surrounding body work.
The primary and secondary inlet manifold gaskets have been replaced. The inlet manifold vacuum test is within tolerance.
So. What the heck am I missing here?! IS it an exhaust leak, if so where? Could this be an inlet leak?
If needed I will upload an audio file of the leak.