Just bought a 1998 Expedition (Eddie Bauer) and it ran perfect for the first few days.
Not realizing the keys were chipped, I had an extra set made and went to start it up with the non chipped keys. (my wife had the original key) It made a real rattle sound the theft light came on and it stalled. Now that I realize those keys are chipped, I used the original key, and it still makes the rattle at start up. It is a 5.4L with about 118,000 miles.

Any ideas? Could I have damaged something using the store bought key?

 

I hadn't taken it for a drive since it was making the sound. Decided to take it out for a quick run, and the rattle seems to have gone away. Hopefully it stays away.

But if anyone else has ever had this or has any insite, please post.

 

I have the same problem. When I first start my 99 Navi, it rattles for a bit from the front of the engine somewhere the after its warm it stops. I am thinking either a belt tensioner or timing chain tensioner.

 

Possibly the ac is on. If you have the auto climate function the compressor engages when you start up even if you're not using the ac to cool off.
Try starting the truck with the auto climate off. Try again with it on. I think the compressor runs because it is removing excess moisture in the air. The clunk or rattle is the compressor clutches engaging
Maybe this helps, maybe not...

 

Thanks for the info guys... I'm not even sure if I have auto climate. It might. I only bought this truck 2 days ago and it has so many bells and whistles I can't even comprehend. I'm used to my 93 Explorer XL which had no options and no problems.

But I am definatley going to take your comments and look into both. It gives me a little peace of mind to hear it doesn't sound too serious.

 

I will try this in the morning. Thanks for the input.

 

The most common thing I see with the modulars that have that rattle are the timing chain tensioners bleeding down,or the lash adjusters bleeding down.That's typically caused by using a filter with a crappy anti-drainback valve(fram,etc..).
JL

 

I second that. I changed from Fram to Motorcraft oil filters on both of my 5.4's and it was surprising how much quieter they started.

 

The modular motors sometimes have a problem with piston slap as well.

 

Yup mine has a little piston slap in the morning when it is really cold out (40F and below) I just let it warm up for a while until the noise goes away.

 

all you guys are weird. the noise your hearing is the air ride compressor kicking on. when its done leveling out it will go off.

 

Not all Expedisitons have the air suspension.
JL

 

.....and if they do the air compressor shouldn't make a rattling sound.

 

bought 97 EB a few weeks ago and have never had any strange rattle with the 5.4 -- sometimes noises but nothing loud enough or odd enough to draw attention.

 

The air compressor in mine is pretty noisy on start up. It kicks on about 80% of the time when it's started. It works fine, it's just a little bit noisy.