Hey guys. I'm new to the forum but not to my truck. I have a 2000 Navigator 5.4 that has started making a knocking type noise. I've searched around these forums and haven't seen someone with the same exact symptoms so I'm starting a new thread. I have no issues when the truck starts. Everything sounds normal there. However, when going freeway speeds I will hear what I'd describe as a knocking or metallic rattle. It almost sounds like something is loose and rattling under te engine. It happens almost exclusively while going freeway speeds (I consider that 50-75mph) and while going uphill. From time to time I'll notice it on a level surface at the same speed. I don't hear it while in the city at all.

Any suggestions out there? I took it to a local shop a few weeks ago and they werent able to find/hear the noise I was hearing. I did a tranny flush, oil change (I was due anyway), spark plugs & boots, pcv valve, and filter (air & fuel) replace. The knocking is still there but I can't really tell if it got better or not after the service.

Suggestions on my next steps?

 

My fiance drove the truck yesterday and she described the noise as being similar to "being in 6th gear and going up a hill." Which I guess I could agree with.

Anyone have any ideas for what I should look in to? Any help would be greatly appreciated.

 

Did you look to see if there is anything loose or rattling under the engine?
Loose mufler clamp? Loose heat shield?

Bang on the cat with your palm - is it rattling inside?

Is the engine overheating? Low on oil?

 

sounds like a COP going out that hasn't thrown a code yet

 

Take it on the highway and when it makes the noise shift into neutral. Take note if the noise goes away when the engine RPMs drop or if the noise follows vehicle speed.

 

Does this year Nav. require 91+ octane?

My '03 Nav. does require the 91+ octange fuel. Maybe try switching to premium gas and see if that takes care of the knocking noise?

 

Thanks for the suggestions guys. I'll do a little engine sleuthing this weekend to see if anything pans out.

Good idea. I'll try this on my way to work this morning and report back.

On a seperate note, is there any chance that this is related to the suspension? The reason I ask is because yesterday, I was on my way home and began ascending the same hill that I normally hear the noise on. I noticed that the "CHK SUSP" light came on moments before I began to hear the noise.

I'm in the process of converting the Navi air suspension setup to the Expy Spring/Strut setup (via strutmasters.com). No work has been done yet but I am aware that there are some gremlins in the air ride that I'm tired of throwing cash at, hence the conversion. I've noticed the light coming on in the past but never actually witnessed when it comes on. It might be coincidence but I figured Id mention it anyway.

Anyway, thanks a ton guys. I know we'll figure this out together!