thank you for the help. i think i will drive it till it blows and replace the motor. im thinking piston slap but who knows i might get 10k more miles out of it or maybe notwhen it does go i will let you all know what it was. i changed the oil 2 days ago and added some lucas oil treatment to it but it made no change in the sound. i also used castrol hd 30 oil . i will just wait to see what happens.

 

If it is a deep sounding knock coming from the top end it could be a collapsed piston. I heard from an engine rebuilder once that almost every time he does a 4.9 he will find at least one collapsed piston inside. Maybe I am wrong, but its a possibility.

P.S.-I would just drive it until it blows, as long as you don't take it on long trips. You could always buy another block from the junkyard and rebuild it when yours goes out.

 

I had the same sound with my 300 before I sold it. Had a fresh long block and after 2000 miles, you could hear just a faint knock that sounded like it was coming from the #2 rod. Wasn't always there, but sure was strange. Never had any problem with the motor. 300's are a strange beast but one of the best motors Ford ever built.

 

man when i do an oil change my motor runs dry for about 20 seconds... i hate to do changes do to that fact... it just kills me to hear EVERYTHING clanking clunking tappin clackin... etc

 

I hear a slight knock on mine sometimes. But I've come to the conclusion it's quite likely the fuel pump. Sometimes is almost sounds exactly like a slight loose con rod bearing, but it doesn't do it all the time. It only does this when hot, and fully warmed up. My oil pressure is always real good. "45-55 lb's" average most all the time, even at idle. Doesn't drop as it gets hot. I've tried using heavier oil, and it seems to maybe help a bit, but still does it sometimes. It's weird. You don't hear it much at idle, but hear it if you slightly increase the rpm's.
I don't notice it at driving speeds much as it's not loud enough.
But I've had times when it was doing this, and using a hose, it seemed to be coming from the fuel pump, and radiating along the camshaft I assume. One of these days when I feel really energetic, and have a spare gasket, I'm gonna yank the pump for a few seconds and see if it will go away. Some times, I'll go for days and not really hear it.
Then it will crop up again...Heck, I might just get a new pump, and keep the other as a spare. They are cheap...
I had 20w-50 in it from the summer, as I was testing that oil for the knock. The engine seemed to like 20w-50 overall, and ran quiet, but I put 10w-40 back in it for the winter, just the other day. I wanted a bit better flow when it's cold. But I'll probably go back to 20w-50 this spring.
If not a synth oil...I'm just at 4000 miles now. I was considering maybe going to synth oil at about 5000, but haven't decided yet. I change my oil often, and probably still would even with the synthetic oil. It would cost quite a bit more being I dump it fairly often.
BTW...The 20 second tap at oil change shouldn't hurt anything as long as you don't rev the engine at all until the light goes out. But you can speed the flow by either prefilling the filter, or using a drill on the oil pump and prepriming, or unplug the coil, and use the starter to prime a few bursts before actually starting. I do #3 usually. I'll unplug the coil, and crank about 10-15 seconds a shot, about 2-3 times. Then start it and wait for the light to go out. Should be real quick if you prime the system. What's scary is a auto choke in cold mode....1500-2000 rpm with no oil pressure is the pits. I'd always preoil with a fast rpm auto choke. My choke is manual... MK

 

You may be able to get the TSB from your local Ford dealer. You can search Alldata's database at www.alldata.com . I believe the TSB is titled " Low end knock ".

Mine has been doing this since 30,000 miles. It hasn't gotten much louder since. Right now I'm at 200,000. You may get a lot more than 10K out of yours, even if the knock is pretty loud.

 

If you have a fuel injected motor, floor the gas pedal while cranking, that will put the computer in flood clear mode and allow you to build up oil pressure before starting the motor (after an oil change, etc). As long as the throttle is wide open while cranking, it will not fire.

 

bigbadjs,
you were correct with alldata. they do have a tsb listed for the 1990 4.9 liter titled lower end knock but would not describe with out subscription (*******s!!!).after an oil change and lucas oil treatment the knock has not changed at all. it is still loudest when cold and less after warming. im still convinced its piston slop and may be terminal.thats why im shopping for another motor. i will still monitor this thread and post what happens

thanks folks


MERRY CHRISTMAS !!!!!!!!!

 

thanks steell , but i think this will be one of the last oil changes for this 4.9. as much as i hate to say it because the motor still runs great. it makes no sense. i guess its a ford thing . i know the 300 6 is a tough motor and can live through almost anything. who knows it might last through the winter but im still looking for a backup any how. thanks for your advice.

 

Hey, regarding accessing the TSB description, I found out my local public library subscribes to alldata and heard a lot of them do. Maybe yours, too?

 

It's $25.oo for a year subscription and about $15.oo for renewals and adding another vehicle. I have one but I'm not sure if it's a good idea to copy and paste the TSB from there!!?!? However, there are several mentions about an accelerator cable bracket causing a buzzing/vibration and apparently it can also sound like a lower end knock in the cab also?!?!

 

A rod (or rods) will only knock when there is no load on the motor.
For instance, rev it to 1000 rpm in neutral and hold it there, if you have bad rod bearings it will hammer. Rods do not knock under accelleration or decelleration, only under no load conditions.
Main bearings are the reverse, they knock under load.
Piston slap is loudest when cold, and gets quieter/goes away when warm (as the piston expands from the heat).
My motor has both rod and mains hammering, I think I am going to lift the motor up a little and drop the pan to replace the rod and mains, later this week. It's only around $50.00 for rod and main bearings and a oil pan gasket.

Steve

 

thanks steve
the noise will soften as the motor warms but never goes away totaly. when cold it hammers pretty good. i'll just baby it till i can find another motor to replace it with and maybe rebuild this one if the cylinder is not beat too bad. like i said the motor runs good . good power. no smoke. how can i not keep driving it?

 

I was advised to use GM top engine cleaner to correct pinging due to possible carbon buildup. Well , it didn't fix the ping but I havn't heard that cold engine knock since the treatment. It looks like this knock wasn't piston knock afterall but carbon knock. I'll wait for the real cold weather to set in to see if this is fixed for certain.

You can get this treatment from your local GM dealer. Get the canned version, not the spray. Start the engine- hook a vacuum hose to the vacuum tree on the manifold and place the other end in the can. You'll have to dip the hose in and out of the can because it will suck the whole canful real quick. After the treatment, shut the engine off and let it sit for an hour or so. Your manifold and cylinders will be saturated with the cleaner so those detergents can get to work on that carbon.

Start up the engine and Prepare for an impressive smoke display, rev the engine up real good. The smoke lasts for 15 minutes or so.