91 4.0 knock

[mjohns]

Hello All,
My 91 EB Explorer has been knocking for a little while now, it happens in the mornings when I first start it up. It comes and goes for maybe the first 5 minutes it is running. (knocks for a few seconds then stops for a few). It usually lasts about 5 minutes then after that you can't hear it at all. I cant tell where its coming from, (I'm planning on getting a stethoscope soon because this is starting to drive me crazy). I've done plenty of searches about lifters, rocker arms, knocking, etc. and learned lots of useful information.
My question is, If this is a rod or bearing knock would it come and go until it warms up then stop completely or would it be steady whenever the motor is running? I'm hoping its not that serious. It only uses about 1 to 1.5 quarts of oil between changes (every 3000 miles I have used fram and motorcraft filters both), It does have a small leak, so thats were some goes. The factory oil pressure guage usually shows about half way, I've haven't really seen it fluctuate.
Thanks for any help, and this forum rocks.

 

[monkeydude3]

well if it goes away, it may be the lifters. On my mom's old mercury villager minivan it did the same thing y ou describe until warm, and then nothing. Now is this a hard knock sound or a light ticking is what I need to know.

 

[monkeydude3]

A connecting rod knock would get considerably louder the hotter the engine got. This is because the cold oil provides a cushion from the rod to crank, and as it thins out the cushion goes away.

 

[mjohns]

It sounds like a fairly hard knock to me, I could just be paranoid though. I really don't have much to compare it to. Thanks.

 

[monkeydude3]

hmmm, does this knock come with load too? I would try decarboning the engine with seafoam first. May just be some carbon buildup.

 

[falls guy]

Oil pump? Pick up screen could be dirty? Probably a rod or bearing noise. Once it heats up, the metal expands and bearing clearances get smaller.
Good luck
Peace

 

[Rick]

Lifters can make a load rapping noise which goes away once the oil pressure comes up. There is a good chance that's what it is.

 

[falls guy]

Ya. Is the noise coming from undernieth or from the engine bay? I'd flush it either way and put some Lucas oil additive. That'l tell you more.

 

[jordan23]

Not necessarily lifter noise. I have the same 'sound' coming from my engine...and was told it was a noisy timing chain tensioner...

Jordan23

 

[BigDakota]

Knocks are a real difficult to figure out sometimes. A "double sounding knock" when you rev the engine or under a heavy work load is a sure sign of a rod bearing going bad! Lifters can make some loud knocking noises if they are "dry". A high mileage engine will have what is called "piston slap" sending out knock noises., but that usually happens when the engine gets warm.
Find a way to make your engine pull hard "torque" and listen for any noises. Hook up to a heavy trailer, put your emergency brake on hard with your brake pedal pressed and try to take off"automatic is easy this way", or find a solid,not movable object to push against with your front bumper and gradually step on the gas pedal and listen for low end engine noises!
This is no guarantee to finding your solution, just another probability test!

 

[DeerHunter]

I had a 5.0 with a loud knock at startup that would go away when the engine warmed up, turned out to be a hairline crack in the #4 piston. I know that's probably not what you wanted to hear.

DeerHunter

 

[rookieshooter]

I'm leaning more to a lifter also, sounds like its not pumping up. I'm going out on a limb, but I really do not think its a rod. Due to the fact that it goes away. If you had that much air space between rod bearing and crank journal to hear a knock, you would hear it constantly. Like Dakota said, a double sound, due to the recipicating action of the rod.

 

[mjohns]

Thanks for all the replies. I'm going to try some seafoam when I can get to town to get some. Hopefully this will help.