my 98 Expedition 4.6 Windsor is making noises, starts out as light tapping when first cranked, as it warms up tapping gets louder and harder. When it is being driven, it runs pretty smooth, stumbles a little bit which I think is fuel injectors, 224,000 miles and have never had injectors changed. Planning to do it after Christmas is over. Anyway, when I come to a stop, the tapping is pretty loud and hard. Have had several people tell me it was everything from timing chains slapping to main bearings knocking, to the exhaust manifolds maybe having a broken stud. So far it has been too cold and raining most days to check manifolds. Bottom line, it still runs ok but sounds like my grandfather's old diesel tractor. Any clues what causes this? Too broke to take it to a shop so I do my best to do my own repairs.

 

Is it more of a ticking or knocking noise?
Does your oil pressure drop off significantly after it's warmed up?
Has your MPG fallen?

 

it starts out as a ticking or tapping noise when first cranked, but after it has been driven a few miles it sounds more like a knock, it is much louder. can't pinpoint it, but you really hear it better by putting your head to the tire wells on both sides

 

oh and by the way...no check engine lights, oil pressure stays steady, MPG is roughly the same

 

Well that rules out the top of the motor for things like loose spark plugs, vacuum leaks, and injectors. This narrows your problem down to either exhaust manifold leaks or a spun bearing. Considering the level of noise, you can probably rule out a spun main bearing since those make noise under load and not so much at an idle. Now you're left with the exhaust manifold leak or a spun rod bearing. The noise increasing as the engine warms up points to a rod bearing, however with a spun rod bearing the oil pressure will usually be good when cold and drop to almost nothing when the engine is hot and that isn't happening.

You're kind of down to exhaust manifold leaks as the problem, although I can't be 100% sure about it. You can try to narrow down the noise location further by using a 3 foot (or so) piece of hose. Put one end to your ear and move the other end around to various places around the exhaust manifolds to see if you can pick up loud spots. You cannot feel for leaks due to the radiator fan running all the time.

 

part of that noice sounds metallic, as if the heat shields on the cats are vibrating, and if we get a break in the weather I was going to check the manifolds for a broken stud...I have heard that is common

 

Yes it is very common for your model year. The best way to check the studs, or use the hose as I mentioned is by removing the plastic wheel well cover. This allows you to look right over the top of the front tires and get in there real nice.

 

The only problem I see with the diagnosis so far is that exhaust leaks at the manifold generally start out loud when cold and get quieter as the truck warms up. They also rarely sound like a heavy metallic knock.

I hate to say it but it sure sounds like rod knock to me. They get worse as the engine warms up. It is a heavier, metallic sound. As it gets progressively worse you will see an oil pressure problem but not necessarily early in the failure.

I wouldn't rule out the leaky manifold, just sounds more like a bearing to me.

Good Luck

 

what mileage does the rod bearings fail in an engine that has been maintained?

 

I do not think you can put a number on that. Everybody has a different definition of "maintained". We also drive mass produced vehicles and tolerances vary to some degree on everything from materials to assembly.

My company truck was well maintained by the first manager who drove it for just over 100k miles. The next two guys were total bozo's and they put another 140k between them. It has 255k on it now and still runs pretty well. It makes some interesting noises now and then, and I'm not ready to drive it cross country, but overall I think it still has some life in it. I had the front end rebuilt and a complete brake job so it rides and drives well. The 5.4 still has good power with tolerable oil consumption of 1qt per 3000 miles.

You just really never know. If it is a rod, I still think 224k is pretty decent. 25-30 years ago most cars were trash by 100k miles.

 

maybe metallic knock was the wrong term to use...it is more like a metallic rattle or vibration in conjunction with the light tapping at startup that gets louder when engine has been driven and comes back to idle

 

Light tapping and rattle sounds more like valvetrain or manifold gasket. Have you done an oil change recently? Is the oil level correct?

I might do an oil change, examine the oil that comes out for metal, and cut the filter open looking for the same.

It is extremely hard to diagnose a noise we can't hear.

 

To me it kinda sounds like timing chains. The chain guides have teflon tensioners that wear out. mine were worn down to the metal and left shavings in the oil pan. Change the oil and run your fingers through the oil (I think mine were made of alum). But I wouldn't rule out the other stuff either...good luck

 

I would start by checking the manifold studs first, then would go and install a real oil pressure gauge as if you are relying on the one on the instrument cluster which is basically and idiot light with a pointer, you might be surprised how much your oil pressure is changing.