Tapping or knocking noise. Need help identifying.

[caracasmc]

So let me try and give as many details as possible so hopefully someone can point me in the right direction:

2003 Explorer XLT 4.6L 8cil. 89,000 miles.

About a week ago I started my car up to go to work and noticed a knocking or tapping sound. It has continued every day. I can't say it has gotten any worse. Seems to be the same as when it first started.

I pop the hood and the noise is not as pronounced from the hood area. In other words, I can't hear it as well from above the engine under the hood. I walked around all sides of the hood area and the sound never seems any louder.

I follow the noise down to under the car where it is much more pronounced. I haven't been able to jack the car up or anything yet and get under it. I've only laid down and poked my head under the car behind the driver side wheel. The noise definitely seems loudest underneath and somewhere between the two front wheels (or at least that general area).

The noise happens in Park, Neutral and in Drive. If I accelerate, the noise speeds up. If I decelerate the noise slows down. It's a very consistent tap tap tap tap tap tap tap, etc. When I pull out of the driveway and start down the road I can hear the noise echoing off cars as I go by, etc. If I slow down at a stop sign it gets slower and seems slightly louder. When I accelerate it gets faster but quieter. At highway speeds I do not notice the noise at all. And if I travel a longer distance, say across town, at decent speed, when I come to a stop the noise does NOT reappear right away. Even if I sit there for a while with the engine running it doesn't start tapping. It will usually start up again after I have left the car off for an hour or so.

I do not "feel" the knock in the seat or floorboard or steering wheel or anything like that. No thuds or banging that can be felt. Just a consistent tap tap tap tap tap tap.

I live in South America where it's 80-90 degrees year round. Wet or dry seasons only. No salt. I've used Shell Helix HX7 Semi-Synthetic oil. Almost all city driving. Terrible roads. Lots of holes and ruts.

Not sure what else to say. My worst fear is that it's a piston or rod, etc. I have a mechanic coming on Monday to look at it and see if he can locate the source of the noise. I plan to take the belt off and run it for less than 60 seconds to see if it's related to anything spinning off the belt. I also plan on having him check the exhaust manifold for leaks or broken studs.

Also, I did run the car for a month or two with a bad or failing ignition coil. The motor would shake pretty strongly. I finally got it into a shop and they replaced a bad coil and it took care of the motor shake. Interestingly, the shake started up again right around the same time as I began hearing the noise. Maybe a day or two before the noise started. Could it be related to the ignition coils, spark plugs, ignition, etc? Not sure if it's related since I don't hear the noise from under the hood but rather from under the car.

Could it be something with the transmission? Had the transmission rebuilt about 6 months ago. Haven't had any problems with shifting or anything like that. Feels like new in that regard.



Anyway, hopefully someone can point me in the right direction here. Is there anything specific I should ask the mechanic to check out other than what I mentioned above?

Thanks so much for the help.

 

[zpn_by]

generally speaking, noise from the bottom end will likely be a bearing, either crank, rod, or piston (wrist pin). The lower the noise, the more likely that it's a crank bearing or a rod bearing. Have you seen any signs of coolant in the oil? Have you done an oil change, and if so, have you noticed any metal filings in the oil? These would be the signs I'd look for first. Judging by the time, your mechanic friend should have had a look at it by now - was he able to determine anything? I hope for your sake that it's not a bearing, but it's hard to think that it would be anything else, based on what you describe.

Having said all that I did above, it's next to impossible to diagnose a sound based on a written description of it. I've given you my best guess, but that's all it is. Good luck, and if you're not able to get anywhere otherwise, see if you can put up a sound clip (or link to one) for some of us to listen to and maybe get a better idea...

 

[caracasmc]

Thanks for the reply. Unfortunately, my mechanic friend has not been able to make it over as of yet. But fortunately, I seem to have fixed the issue by changing out all of the ignition coils. I have no idea how this fixed the problem. The noise was very quiet at the top of the engine and very pronounced underneath. Not sure what changing the coils would have fixed. Is it possible that a bad coil caused a cylinder to not fire and the piston or rod was tapping due to that?

I'll update in a couple days and let you know if the noise has started up again.

Regarding oil, no coolant noticeable in oil. Also no metallic pieces. Oil looks fine.

 

[Number4]

You could try one of these. Usually about $15 at most parts stores.

Put it against the engine (running) to see if you can pin point the noise.

http://www.amazon.com/Lisle-52500-Mechanics-Stethoscope/dp/B0002SQYSM

Where goggles and don't touch moving objects with it. You will, it happens, just try not too. That's why you wear goggles.

You can put it on pulley bolts, etc. parts that are stationary.

Great cheap tool to have in the arsenal.

 

[caracasmc]

You could try one of these. Usually about $15 at most parts stores.

Put it against the engine (running) to see if you can pin point the noise.

http://www.amazon.com/Lisle-52500-Mechanics-Stethoscope/dp/B0002SQYSM

Where goggles and don't touch moving objects with it. You will, it happens, just try not too. That's why you wear goggles.

You can put it on pulley bolts, etc. parts that are stationary.

Great cheap tool to have in the arsenal.

I'll have to pick one up next time I'm in the states. I live in South America. I've
wanted one for some time now but haven't purchased one as of yet. Thanks for the tip.

 

[Nomad8326]

You can use a long screwdriver in a pinch.

 

[Nomad8326]

How To Find A Noise - EricTheCarGuy

 

[caracasmc]

So, today is the second day driving since changing the ignition coils and the noise has not returned as of yet. Seems to have fixed the issue. Does anyone know how changing the ignition coils could have fixed the tapping noise? I had one mechanic tell me, after a very brief and superficial look and listen, that it was either a piston or rod. Had my dad take a listen and he thought the same thing. But after changing the coils, the noise is gone. Any ideas what could have been happening?

 

[EricW2676]

I had the same issue with my 2002 Explorer. The noise would go away and I would think it was fine, but always come back. The issue with mine was the timing belt tensioner and guide failed on the right hand side. In the process of this failure one of the cam journals on the side of the failure was galled up pretty bad, requiring head replacement.

I am now in the process of replacing a RH head assembly,oil pump and pick-up tube, egr tube(broke it removing the engine),water pump ,entire timing chain assembly,and all gaskets.

You may want to check into this as a possibility of your engine noise.

 

[Number4]

The only thing with a coil that I can think of would be an arc. You'd have a misfire though, rough idle and you'd see the arc.

Keep in mind that working in cars causes odd things to happen. I don't know how many times I've dealt with a car coming in for work and something untouched and unrelated fails while the cars in the shop. Every time, the customer thinks the shop did something. Murphy's law I suppose.

Tapping and knocking is usually something failing inside. Either on its own or due to no oil.

You haven't been running Penzoil have you?