I just purchased my Explorer 3 weeks ago (see specs in signature). When I start it up in the morning, I let it idle for about a minute (to get the oil going to all the right spots) and then I take off. I notice that there is a PUT-PUT-PUT-PUT sound coming from the right side of the engine. It only happens 1>When the engine is cold 2>When the engine is under load and 3>You accelerate moderately-hard. I cannot reproduce it with the hood up and the engine in Neutral. It IS RPM dependent. It last for quite sometime, probably 10-15 minutes after starting.

This sound almost sounds like and exhaust gasket leak (where the exhaust manifold connects with the pipe), but it seems too low. Could it be a leaky spark plug seal (spark plug not seating properly)? Is this a normal noisy associated with the smog equipment? I had a Ford Bronco with the same 5.0 engine and it never made a noise like this.

THANKS EVERYONE!

Yup! Its an exhaust leak. 5.0s are very prone to this.. especially the passenger side. Here is a thread with some reccommended gaskets and bolts you should get to help keep these manifolds from leaking. But also look for a crack on that side. Some manifolds have a tendency of splitting and you use to be able to get headers as a cheap replacment.. but now you'll just need to get new manifolds. :(


http://www.explorerforum.com/forums/showthread.php?threadid=83255&highlight=headers