Hey everyone!

I tried posting this in the thunderbird forum but after 4 hours and 5 vies, and seeing this forum has 33 viewing it, seems like I may get someone to help here!

I just bought the other day a 96 thunderbird and I have an issue and think I may need a new head.

After I bought it, from private party, I noticed it was 3 qts low on oil. First bad sign of trying to hide something. So I topped it up with the proper level and drove it, and everything seemed ok.

the engine is smooth, sounds great, but while accelerating on a bridge with concrete walls I heard it, sounds like a knock. Puzzled, I went home popped the hood and rev'd it at the TB. sounds good. no noises at all. Up and down, sounded good. So, went for another drive. I still heard it, now that I was payin attention I heard it, consistent knock above 2500 rpms. But could not replicate the noise parked.

So today after driving it home from work, about 20 miles, I can hear it faintly on the highway at 22rpm sometimes. And it does come and go.

So I had the ac on and this time I could replicate it parked. And it is tough, I have to float the rpm's at about 3000 and let it drop and I can pick up on it. Its coming from the back driver side. I think thats #8 cylinder. It is noticeable, and it sounds like it is coming from the upper end of the engine. I have tried to research but have been left with no conclusion. Its the 96 4.6 with exactly 200,000 mi on it.

With how it sounds I do almost feel if is valve train noise and is only on one valve. Like maybe I have a weak valve spring, or a bad HLA. But i don't want to drop a valve and destroy my head or worse.

So I was hoping to find a 4.6 guru that can drop some knowledge upon me. I am really fond of these ford mod motors but this is actually my first. Typically I only buy probes, but I couldn't find one. lol. And I know the HLA on the probes always made noise, but this one is a little more metalic and does get a little loud at upper rpms. But only under a load. You can barely hear it and HAVE to have the AC on to reproduce it in park, and it is only about 2500 rpm or higher do I hear it.

I work all week, but I plan to grandma it all week and keep the rpms low. So the noise doesn't happen, and wanted to dig into it this weekend. I would appreciate some input, its hard to search for, "4.6 2v upper end engine knock under load" and come back with anything useful.

Thanks in advance!!!

And after some research I found its a Romeo 4.6

 

Well, this really is just about as basic as you can go with engine work. Is this noise present when the eng. is cold, or doesn't it matter? And it's only under load? have you disconnected the fuel injector or spark plug to see if the noise changes?
These are a few things to think of. If you can't isolate the noise beforehand, you'll have no idea where to start; use a stethoscope or screwdriver to listen to various points on the engine and see if you can isolate it; it makes it easier to repair.
At this milage, just about anything could go, but don't worry, we'll get it fixed./

 

Doesn't matter hot or cold. On throttle or off, at around 2200-2500 rpm the (I am calling it a knock) starts. With a stethoscope I can not hear anything. the only time I could replicate the problem was earlier today one time and it was so brief I really couldn't make any judgement other than I thought it was coming from the top end. Otherwise the only time I hear it is driving. I did not disconnect the injector. I read that and was on the fence about it. That's why I came here. I didn't know if this sort of thing was common, or if someone off the top of there hat would be like, ya it happens, its this thing. I was hoping at least...

I bought it yesterday morning and have driven it 155 miles. I know advanced can get me a reman head for 300 and change if need be.... I have been reading a lot of threads about cam guides and such and the head could be shot. But most of those are ticks/knocks at idle, and mine does not do that. At all, even at cold start its quiet.

And the dummy oil gauge doesnt move as fords do.

Thanks for the help, I knew this forum would be quicker. lol

 

After watching 20 pages of "4.6 valve knock" videos on youtube I don't know. It sounds as though my sound is at the same pace as the ones Idling. But mine is above 2k rpms.

I didn't go unhook the injector, I was, but I am tired and will do it after work tomorrow.

If unhooking the injector makes it quiet, does that mean its a rod bearing? Or an injector? Is it possible to do rod bearings in car? I haven't looked underneath to see if there is clearance by the K member.

Also, the knock sound I hear, compared to the videos I watched is not the same. It is about that volume, but it is sharper, and constant. Shorter. It is not a tick sound I hear. I wish it was a tick.

 

Usually, the disconnection of fuel/spark, which kills the clyinder's contribution, will tell you (and remember, I said USUALLY) that it's a bottom end problem if the problem changes signifgantly.
Since this seems to be a tough noise to diag, listen carefully; is it a 'double knock' that would delineate the connecting rod, or is it heavier, which would be more rod bearing. If it's pretty deep, it could be a main bearing.
Please let us know!

 

Ok, unhooked injector #7 and then #8, no change. It isn't heavy or deep, but louder than lets say my old integra that I bent valves in.

I had to do a lot of driving today and now have put 224 miles on it since sunday. And today I noticed some things:

At highway speed 70 mph on a flat piece of road I can hear the knock, if I give it just a little gas, enough to barely accelerate it will go away, or if I completely let of the throttle it will go away. There is a sweet spot just a small amount of throttle I can make the knock louder or quieter.
I also noticed it seems to be more frequent on deceleration. The few times I gave it some gas I noticed it was a bit slower on acceleration than deceleration.

It almost seems to me, like I have a bad rocker arm. Or maybe a flat lobe on my cam. But at the same time, I have had a few assumptions I have put together that maybe will tell more to the tale. The previous owner just bought a brand new ford focus. And it being 3 qts low on oil. I almost feel as though he brought it to ford to look at, they told him its a bad bearing and sold him a new car.

I remember reading somewhere but there have been soo many threads I have read I can't remember what its called, but something about the top ring of the piston having issues? I wish I could remember or find it. If I do I will post it.

I just want to be able to diag it so I can fix it properly. I dont want to put heads on a bad bottom end, and I don't want to rebuild a motor "HOPING" to find the cause. Been there done that. If I can at least determine that its not gonna bomb on me I would go buy the $350 4.6 with 90k out of a 97 bird on craiglist and rebuild it and flop it in there in a few months.

The only other things I can think to do is remove the valve cover and see if anything looks wrong, but because it is silent at idle I would imagine it would be hard to find. Otherwise I will have to wait to get my scanner till this weekend, a friend has it. And I will have to run some driving checks to watch inject pulse, see if it gets a knock reading, and so forth. I dont have an awesome scanner just an otc genisys so there is only so much I can look at and control.

 

Something you can check, make sure the trans converter to flywheel/flex bolts are tight.
Loose converter nuts/bolts can sound just like a connecting rod noise.

 

This is really off the wall, but pull the PCV hose and plug it. I had a tech ready to pull heads and it was a weak spring in the PCV causing the rattling noise. Might not be it, but is a cheap fix if it is.

 

After you check all the simple things, might not be a bad idea to run a compression test on all the cyls. Might disclose a hidden problem. If all is well, then you can get into more detailed checks.

 

You know, I was just thinking about this at work today, and while I wasn't dropping transmissions on the floor, I was thinking about a possible torque convertor knock; it's really odd that the noise would be more pronouced on a decell rather then accell. But the only problem is, is since it's got to be loaded to reproduce, I don't know how to diag it.