My truck is a 1991 F250, 460 with about 180,000 miles on it. I'm currently having a wierd tapping sound, that only seems to happen when I'm driving. It only does this when I accelerate, when I let my foot off the gas, it will quit. I tried a higher grade fuel, tried carbon cleaners, and re timing. Still doesn't seem to have fixed it. I just noticed this will only happen when I'm driving; not in park.

 

then its in the drivetrain, not the engine

 

Sounds like you have piston slap or a bad main bearing to me.

 

Could possiby be an exhaust leak sounding like mechanical noise.

 

I agree. 460 manifolds are prone to warping. Exhaust leaks can sound like lifters

 

I have gibson headers. I went to tighten the bolts, it feels like one stripped out. I will have to pull the bolts when I get a chance and make sure none snapped.

 

The fact that it's present while under acceleration and goes away when you get off the pedal is an indication that it's an exhaust leak, probably a manifold leak.

These sounds are similar to lifter tap from inside the engine but if it were the lifters it would be a constant tapping sound that is RPM dependent (increase/decrease w/ RPM changes). Since this sound goes away when you're off the throttle, we know it's not the lifters.

Open the hood and get down near either side of the engine while playing with the throttle (can just use the linkage on top of the throttle body) and listen for a leak.

I think the 460 is the same as the 302/351 where they are big/heavy cast iron manifolds with a machined surface. They don't use a gasket between the head and the manifold. Over the coarse of 15 years they eventually warp or even crack in the manifold and need to be replaced - most just use this as a time to replace them with nice headers.

It might also not be warped or cracked...both my 302 and 351 had missing manifold bolts when I took them out. They must have vibrated loose however long ago. The 302 didn't have a leak even though the bolt was missing. The 351 had the same problem but I found another source of the leak and am not sure if the missing bolt(s) contributed to the leak.

Retitled thread - https://www.ford-trucks.com/forums/s...d.php?t=399714

 

Still hasn't been fixed. Took it to a exhaust shop, and it isn't coming from the headers. They said it's coming from the EGR area. I disconnected the electrical harness from it and it still leaks. Will disconnecting the harness still allow air to cycle through?

 

The EGR tube could be leaking. The one on my Ranger got a 4 inch crack in it, close to the EGR. I thought for years the lifters were tappin. Turns out the EGR tube was junk. Replaced it and she's good as new now.

 

Just went through and put a nice cam in, along wtih new lifters, etc. Everything looked great there. I bought a block off for the EGR outlet on my header. Just can't get my EGR tube off it's stuck on very tight.

 

Does anyone have any advice on disconnecting the EGR? If I disconnect the electrical should it quit working all toghter? I removed the wiring harness and still had the exhaust tapping sound.