This happened to my cherokee.. try checking to see that all your flywheel bolts are tightened..
if those are tight.. I am stuck
Peaz
LS

before you take the time to take the dust cover off your flywheel though.. an easy trick is to take a length of garden hose and listen through that.. when mine was doing it in my cherokee it would knock at idle, if yours is not doing this, you are going to look a little rediculous trying this...

 

Could it be a rod knock? This sound you describe could be this. You would notice no loss of power, until it actually came apart. Just a thought.....

 

Not always. I had one the other that would be noisy when changing rpm's. More of a rattle though( like loose exhaust)

With that many miles I'd start by looking at the chain. It probably needs it anyways.
Flywheels are USUALLY loader, more metalic sounds, that will vary under load. Also not really hard to tell this is a problem.
Rods, like flywheels, usually change under load but, more dull sounding than flywheel. Seem less noisy too.
Chain is usually constant and goes consistantl w/rpm.


Just my 2 cents.

 

well guys,I'm totally stumped;took off EGR valve and wire-brushed it,still have a gut feeling,somthing to do with emmissions.Called a couple shops and they assume rod knock.I even took it out on hyway and tried to throw a rod but nothings changed.No performance loss!Was told the rod could be bent on other end,but nothings different about truck exept that constant knock, a little louder than a sparkplug arch.Took rubber hose to listen on the head,starter,waterpump,transmission, valve covers and the only place I could hear a dist. sound was on top of EGR valve.It can't be a rod,wouldn't there be other sighs if it was rod? Do U think I should invest in a OBD scanner? thanks to all

 

I wouldn't think that wouldn't think that would help unless we were talking about a "pinging" type of knock.
I don't know if it helps but, I like to use a long handle screwdriver as a stethoscope ( that way I can use it on the exhaust mans too. Have you listened at the intake runners?

Sorry, I'm at a loss here.

 

Suppose that you stacked the rod bearings, both on one side and none on the other. This can happen when they get worn and too much clearance. The pin wouldn't fit right and a hammering knock will be heard constantly on every stroke. The other clearances would be close enough that you wouldn't hurt anything else until the rod breaks loose. Then it can ruin the block, head/valves. It wouldn't show up with any scanner and the sound might be distributed through the block. I don't know how you could check it without pulling the oil pan and head so that you could take the rod and piston out. Since you wouldn't know which cylinder it was, you'd have to take out most of the crank assembly. If one went bad then the other bearings would need replaced too. You have to know your mileage, driving habits, maintenance schedule and compare the history of your engine to what is normal for others like it. Or a sophisticated shop can take an oil sample and test it. As the bearings get worn, there are different types of metal in layers in the bearings and the metal composition in the oil shows up. Of course, hopefully, it isn't at the crankshaft. I'd still hope for loose flywheel bolt. It still wouldn't show up with a scan but might with hose/steth. Pull the dust cover or trans. if needed and check it. It will be a lot cheaper now then later. If it is a rod then you could loose most of the engine. Good luck.

 

My 98 F150,4.6L only knocks at highway speeds. Not in time with the engine like a rod. Sounds more like something loose and moving with the wind. I changed plugs,(didn't fix it). Doesn't effect performance. Guess I'll wait till something tears up?

 

heat shields on the exhaust maybe? That would be my next, simple check. Just wait till it's cool, then roll under it and check things out. Otherwise, I'd go with the flywheel. If there's any metal in the dust cover, That's a clear sign of a loose bolt rubbing on the bellhousing.
HTH

 

May I suggest start looking into a new motor? the 97/98 4.2s had some seroius head gasket problems. It is quit possible that is what it is....check your oil for coolant, and check your exaust for any, even jsut a little smoke.

 

Could it possibly be your radiator fan? Sounds like the same thing that was going on with my wife's car. Took me a while to figure it out but the fan blade had loosened up enough that it was vibrating and making the noise. Since you said it comes and goes, you might want to check into that.