EFIDynoTuning Forum

I have a 03 mach 1 with 97 mark viii short block thats fresh built, 04 aviator heads, longtube headers, everything else is stock. The engine has about 15 miles on it now and has developed a whistling/ high pitch type noise from behind the engine after the first couple of miles. The noise is intermittent and goes away while driving and does not change with engine speed. After you shut down the engine it sounds like its bleeding off. Ill post a video. Has anybody experienced this before on these engines?

Well it will not let me post a video.

my guess would be pcv system. on my turbo fox, much different pcv setup being turbo, I run it the way Decipha recommends and when I had the system mostly sealed up it would create an odd whistle shortly after starting, which would then go away, but on shut down it would bleed off and whistle like you're describing. I couldnt stand it so and couldnt figure out where it was coming from so I popped a few tiny holes in the line to the oil filler neck which thankfully made it stop.

Ill check the pcv system. On my setup its basically a standard pcv valve feeding into the big port on the mach 1 intake and the other valve cover has a rubber hose going to the intake tube. How does decipha recommend to run it?

I had PVC related whistling at idle issues as well. Strange sound. Pull PVC hose and noise goes away. still have not figured out the exact root cause. Probably gasket somewhere with a tiny leak.

You should run yours stock being N/A. The Decipha way I mentioned is specifically for boost. I think the details are in the getting started write up.

I havent had a chance to verify but i think my issue is the idle air control.

Yeah the idle air control valve can induce a whistling noise as well as some intakes.

Well im pretty sure my issue was having the wrong spark plugs. I reused the Mark viii plugs because they were new. After thinking about it for awhile it donned on me that the B heads are 4 thread and my C heads are 9 thread. So i changed the plugs and discovered half of the plug was not in the cylinder and the plug was seated on the end of the threads instead of the tapered seat. After changing the plugs the car idle way better and the noise is no longer there.

See pics.