Engine noise-'99 3.8

Have a 1999 3.8 Windstar LX. Has 150k miles. I performed P0171-0174 fix about 3 years ago. Just recently the engine started making a rattling noise that appears to be coming from front part of engine opposite tranny. I removed the upper intake manifold thinking that maybe it was broken inside and was getting noise from loose inner manifold section. Everything appeared to be OK. The noise is more pronounced at lower RPM and gets worse when A/C is turned on. When engine is reved to higher RPM the rattling almost completely goes away. I removed the serentine belt and ran engine a minute or two to see if the noise may be from water pump, A/C compressor, power steering pump, idler, and tensioner. Still had noise. Motor runs great, no lose of power or MPG drop-off. The noise is not a squeek or high pitched noise. Sounds almost like something rattling loose in engine. I checked the heat shields on catalytic convertors. I have flushed tranny regularly and flushed power steering system regularly. I have not checked anything else. It is about due plugs, wires. Am getting no codes. Any other suggesetio0ns woul be appreciated.

crrobbins

I have had the ceramic insides of a catalytic converter break....causing a rattling sound.
You could have something in the valve train causing a rattle.....
If you need to add coolant from time to time......you could have more serious problems due to coolant in the motor oil.

Of course, like you....the first thing that I thought of when reading the title of this post......was the upper intake manifold internal separation that you mention.

As I have a '96, I am not familiar with the upper intake manifold that you have.

Thanks for reply Wiswind. The oil is in great shape and I have not been adding any coolant. Van still makes rattling noise at low RPM and almost completely goes away above 1000-1200 RPM. It really gets noisy when AC is on at low RPM, but again goes away at higher RPM. Engine also made noise with serpentine belt removed. Would catalytic converter internal damage cause the noise to sound in motor?

crrobbins

Well....I tracked the sound down to the catalytic converter very easily....so with normal hearing.....you should be able to tell.
The injectors will make some clicking noise.....as can the lifters.
If you have a good mechanic that you can trust......I would recommend having them give it a listen.

Update on engine noise. Had a friend with an auto repair shop. He listened to noise and said it sounded like flywheel loose or broken. We put up on his racks and confirmed this. Repairs cost a little over $300. Much less noise now. Having a friend like this saved me some bucks, with me helping. Thanks for responses.

crrobbins

Thanks for the feedback. There have been others who have had cracked flywheels ... but they have been very rare. Hope you have no more "biggies" for a long while ...