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My 2000 5.4 has been making a weird noise and it sounds like its coming out of the exhaust, but the noise is most noticeable around the converters. It doesn't do it ALL the time, but under acceleration at 2800-2900 rpm ONLY and the noise comes in. Sometimes it seems to do it 2 or 3 times (pfft pfft or pfft pfft pfft). It doesn't appear to lose any power while doing this and it will do it any throttle position. If I keep it at that rpm level, the most it will do it is about 6 times. Never under deceleration. Anyone have any insight on this?
I had a similar sound and problem with my V-10. The engine configurations are similar ( it's just 2 cylinders short on the 5.4). The culprit turned out to be a loose heat shield right in fornt of the transmission bell. I know it doesn't sound like a heat shield, niether did mine. The engine vibrations at that RPM range agitate the shield in such a way that it makes a PFFT sound. The way I tested it out was by bending the heat shield out away from the transmission bell just a fraction of an inch. Then drive the truck and see if the noise has stopped or changed.
Have you traced the source of the noise?
Does it happen in park with raised idle?
Exhaust manifold gasket leak??Crack in manifold???
Loose Clamp?? Loose muffler??Loose Plug(s)???? Do you have any idiot lights on?
Check you manifold and gasket.
Check all your clamps.
Check your muffler (loose).
CHECK ALL YOUR PLUGS.
I'll check all of the things that were mentioned. No codes, nothing blinking, new muffler, no loss of power, plugs are good, but no, I have never tried the idle method.