tapping noise in '96 Tbird

I know, I've posted this problem before, but I have a tapping sound that seems to be coming from my exhaust when the engine is under load (either hard acceleration or going up steep hills). This happened after I had
the head pipe assembly replaced.
The 2 mechanics I have had look at it keep calling it "spark knock" and they want to drop the issue at that. What is "spark knock", and what can be done about it? Is it caused by not getting good ignition? I am running premium gas, but that only makes it sound bad instead of terrible. I'm starting to think that "spark knock" is a term given to any sound that they can't (or don't want to) identify. (kinda like sending a newbie to the store looking for muffler bearings)
The car has 145k miles on it, and most people only look at that and say that the car is about used up. I disagree since I'm the only owner on the car, and I know how well it's been maintained.
The main thing I'm looking for here is what "spark knock" is, what causes it, and what can be done about it.
Thanks-
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Brian Steele wrote:

Well if it's not like a snipe hunt perhaps it's timing. To much either way (advance or retard) will get a ping if I recall correctly. I missed the earlier posts. What engine are you talking about?
Frank
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A non working EGR valve will cause pinging under load on any of the cars I've owned since 1973
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F.H. wrote:

It's a 4.6L with 145k+ miles- I've used synthetic oil for about 100k of those miles, changed at 5k intervals. I also did all the trans. maintenance except the first change. Miles put on after about 60k have been mostly in long trips (50 mi each way to/from work). So, engine wear shouldn't be as big a deal as it is on most cars with that milage.
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Spark knock is often referred to as ping. Some mechanics actually call it "the ping of economy" because a very slight ping under acceleration indicates most economical engine operation. I remember your first post but I didn't quite understand what you were asking then. I need some additional information.
Which engine is in your Bird? When you say head pipe, do you mean the one that connects to the manifold at one end and the catalytic converter at the other? Did you have to replace both sides?
I occasionally drive a "93 Cougar with the V-6. I hear the exhaust (I guess) make a slight clatter on heavy acceleration. The sound is kinda like shaking a pipe that has a few pebbles in it. This car has done it since it was new. One pro (?) suggested I was hearing the injectors but I think the noise is exhaust. The pipes are stainless steel and sound travels thru them better than the old iron pipes.
Of course, it is possible that the connection between the manifold and the pipe leaks a bit. I don't know if they still use "dognuts" to seal them but when one used to fail, it could make quite a racket. You could see them leak if you revved the engine while watching at night. Bits of fire or spark would shoot out.
I hope this helps a bit - with a little more info, I'm sure you will get a lot of ideas and suggestions from this group.
PoD

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I think the car may have a knock sensor that senses the knock/ping and causes the computer to automatically adjust the timing. Could the sensor be defective??

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el lobo opined in

NO.... IIRC only in boosted engines.
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el lobo wrote:

That would be something to check. I would have thought the dealer would have looked at that, but you never know. I'll put it on my list of things to have them look at next maint. checkup.

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Paul of Dayton wrote:

I've got the 4.6, and the head pipe assembly was not only the part that connects the manifolds with the converter, but it included both preconverters and the converter itself. (the problem that prompted this was failure in the converters)

That sounds like it. The sound seems to originate not from in front of me while I'm driving but more like below me.

I noticed it first right after I had the head pipe assy. replaced, and the guy that did it put it back up on the rack and we looked it over and didn't see where there was any leak. The new assy is not stainless like the original, but a cheaper metal- aluminum, I think. Someone else suggested an EGR valve as a possible culprit, but I had a dealer look at it, and they found a couple other things in the vac system, but not the EGR valve itself.

Thanks- I appreciate all the help- I work on computers, so this "real world" and "moving parts" stuff doesn't make much sense to me sometimes :-)

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Brian - I can't remember if you mentioned it but, how is the general performance of the car? I have a feeling the noise is "normal", especially that you say it sounds like it's below you. I suspect you are hearing the sounds of combustion as the exhaust hits the pipes. That's what we finally figured out about the Cougar about 199k ago...
BTW, both my CV with the 4.6 and the Cougar with the six will ping on WOT but it seems worse some parts of the year than others. I think it has to do with fuel formulas.
PoD

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Paul of Dayton wrote:

The general performance of the car is fine. Whatever is causing the sound doesn't seem to have any effect on the acceleration.

One of the mechanics I talked to said that might be the case, but I would have thought I would have seen it by now. Here in St. Louie, we are stuck with a 10% ethanol mix (federal air quality regs). I will be going home to KC over the holidays, so I'll try some of their fuel (no corn added) and check the results.
[snip]
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I never noticed much difference in St. Louis fuel and central Illinois fuel. I used to live in Springfield, IL and ran to STL every now an again to shop and play. If you are hearing regular exhaust noise (like my Cougar), I doubt anything will make it go away. I suppose you could have the pipes insulated... some performance guys paint or wrap them to get the catalyitics fired quicker... but I haven't a clue how or if it would work.
Good luck!
PoD

especially
the
finally
WOT
to do

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Paul of Dayton wrote:

LOL, I've been trying to think of an analogy for that sound for a long time. I'm usually good with analogy's but this one kinda stumped me. Thanks. I do notice that mine (4.6) is less inclined to make the sound when it's cold.
Frank
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My 94 T-Bird with the 4.6 would do this. Cleaning the MAF sensor cured it. Pat

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Spark knock is "pre-detonation" mixture ignites when near top compression point but before spark. Or burns too fast. Usually either due to timing too advanced. too lean mixture, or carbon build up in top of cyl.
PAtrick's right. When the MAF is dirty, the PCM thinks there's less air then actually is flowing and adjusts fuel input to match. Thus too lean
You can pull a couple plugs and verify this... if electrodes are burnt away and/or insulators are chalk white, thats your likely problem.
go to
www.tccoa.com and search tech tips on how to remove and clean the MAF.
BUT
USe an electronics cleaner or even rubbing alcohol... NOT Windex or anything else that leaves a film or residue. Do NOT use qTips... use a soft bristle paint brush or even tooth brush.
Of course you have changed air filters
PATRICK T. DAVIDSON opined

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Backyard Mechanic wrote:

Got me thinking. I recently had a problem (also 4.6) where I couldn't get the engine to idle. Happened right after I changed the air cleaner. I R & R'd the MAF housing but didn't do any serious (alcohol) cleaning. The problem disappeared. Wonder if I hadn't just dislodged some dirt when changing the filter.
Frank
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F.H. wrote:

Thanks, guys - I'll give that a shot.
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Hi Bryan, just an idea, check the exhaust flow at the tail pipe. Look for a smooth flow. If it feels like a choppy flow, hold a dollar bill there. If there is a lot of flutter motion while holding the bill there, the timing belt / chain, could be the problem. Just think, if the cam lags, like when the chain / belt is streached / loose, the cam is late at TDC. Then the fuel charge is smaller than it should be. It pings. All the gas treatment, ignition timing effort, is all not producing a result. So as the piston rises to let out exhaust, the valves are still late. You'll get a puff of pressure. Do a vaccum gauge check. Smooth? Those long chains starve for oil, lucas was needed in my 92 Cv to supply oil. With lucas, oil walked up the chains. Tapping noise in engine at startup at all? Tensioner cylinders Failing? These are also going to cause ping.
BeeVee

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BeeVee wrote:

I tried this at lunch, there was some flutter, but the "puffs" were pretty close together. Would this lean toward that it's not too far out of sync?

[snip]
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Hi Brian, You'll need to look at the vacuum gauge readings. See if the needle is fluttering less that 2 inches. If more than 1 or 2" you'll have to put effort into the timing chain area to resolve the pinging issue. The exhaust should be a smooth flow. Premium gas will have little effect. With engine cold, listen for ticking (typewritter sound) and not very small clicks from injectors. Do check your plug gaps. Then the compression, while plugs are out. I you decide to tackel the timing chain ~ start with pass side. While the cover is off check the chain for tension and oil flow. Regards, BeeVee

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