Blah. Rattling.

[ChairOhKey]

I believe I've posted a thread a while ago related to this but now I have more information. Anyways...

I'm getting this rattling sound from the engine after I've driven it for a while. I can hear it when I'm stopped and when I start to accelerate. It seems to go away once I get going. I've hit the bottom of my catalytic converter with a log (I suppose I should use something else but that's all I had at the time) and I heard no rattling. I also got near it to see if the rattling was coming from there and it didn't sound like it. I've heard of the heat shield coming lose so I might try looking at that even though I don't think it's coming from that area but it won't hurt.

It also seems to sound louder when the electric fan goes on to cool the engine. This all happens without the A/C on. I do, however, get a horrible rattling sound when I do turn the A/C which I believe is the compressor because my A/C is warm and I'm pretty positive I have a leak somewhere but that's another problem I'll deal with later.

Any ideas on what I should check out? I've read that it could possibly be a cracked exhaust manifold but I'm not sure how to check that. Would the crack be obvious? If so, what areas should I look at? It's a 97 4.0L.

Thanks.

 

[Matthew Currie]

Manifold cracks aren't always obvious, especially on the steel header type we're dealing with. But you should be able to hear it, and it wouldn't likely be a rattle, so much as a kind of popping or chuffing sound. If you look very carefully down around the branches, you can sometimes see a little carbon or other discoloration around a crack. Otherwise, you pretty much have to track it with a stethoscope. A manifold crack will also often get quieter when it heats up. My 95 makes popping noises cold, but hardly is noticeable when it's warmed up. If the rattle seems to change when you turn on the AC, I'd check the idler pulleys and the water pump, which might be loaded differently when the AC kicks on. I'd also look at mountings of things like the fan shroud, electric fan, and AC condenser. The shroud and fan are mounted only with a couple of little screws at the top and tabs at the bottom, and even when they're right they can rattle a little. You might also try bypassing the switch to the electric fan and run it all alone, to see if it's noisy by itself.

 

[lilredwagn]

engine pinging maybe? next time you fill up, try the premium and see if it goes away.

 

[ChairOhKey]

Fixed it. My idler pulley was lose and wobbling.