I've got a 97 with a 4.2, replaced the lower intake manifold last week with a brand new one, new gaskets on everything associated with the job. I've got this knock that was there before, but since doing the manifold, it's much more prevalent.

It occurs at mid-high RPM's (2k-3k), but only under light engine load, never when accelerating. It's most noticeable when I'm coming off the gas for a gear change. It sounds, I don't know, heavy I guess is the best way to describe it. Doesn't sound like valve or rocker chatter, and I can feel it in the shifter. Lower intake manifold was oiling the intake pretty well, excessive buildup in the intake channels and oil in the coolant before the swap. when I pulled the injectors out of their homes it looked like I had just pulled them out of a vat of used black grease. Any suggestions? Oh and I bought the truck a year ago almost to the day. Didn't realize odometer didn't work till I was half way home with it. The guy kept very good records of maintenance, best I can tell it hadn't worked for 2.5 years and it's stuck around 165k, so she's got some miles on her

 

Did you take care of the little things first ? Well, first thing you do is make sure it has a Motorcraft PCV valve. A bad one or 3rd party valves will mimic a knock..almost perfectly.

 

never touched the pcv, didn't know it could make noise. Any way to check it, or it it just a replace and see kinda thing?

EDIT: Just thought about it, and I dont think that's it because I can feel it in the stick, so I'm more inclined to believe it's a real thing

 

That's good, your thinking! But yea, doesn't matter, check it anyway. Fram valves are more prone to this. But, you'll probably have to change it since it's not doing this at idle. Or if you can run it up into the rpms while under the hood until it knocks, then rest you hand on it... That just tests the valve. If the valves just restrictive, it COULD be causing the knock. A bad PCV valve = slow engine death. It's one of the worst things to get wrong and NOBODY sells one with the proper margins for Ford engines other than Motorcraft. That's what you should keep in mind anyway.

 

Noted, I'll order one and replace it. If I go through the hassle of checking it might as well go ahead and replace it

 

Right, what is it, 5 bucks maybe lol. It's an important little breather. They don't run well half constipated..Do you lol. Yea, don't answer that.

 

Haha I don't run well wide open, any less and I'm lookin for a couch to lay down on!

 

I hear yuh lol.

 

Best I could come up with for a video of the noise. I think you can hear it best when i have the camera by the oil cap

https://www.youtube.com/watch?v=D-WX...ature=youtu.be

 

Huh. Yea, I have to think about that one. Doing that now.... I know for a fact I've heard that noise in the past but I can't put my finger on it. I'm thinking it was with an-others 3.8 Ford engine. Yea, I'm not sure that's a knock nor have I had the opportunity to troubleshoot further. Vid was good enough! - Familiar noise.

Perhaps someone else that's familiar has got to the bottom of that one... - no help beyond that unfortunately.