Knocking Mystery

[99Venom]

Ok here is a good one. ***UPDATE: VIDEOS OF NOISE POSTED BELOW***

The other day during some spirited driving, I shifted from 1st to second at about 6200 rpm and for an instant I felt a loss of power in the pedal and then came a metallic rattling/knocking noise from the engine. I'm calling it a rattle because it sounds like a broken piece of metal banging around, but could easily be called a knock as well. I wasn't far from home so I headed back and parked it in the driveway, the car rattled all the way home.

I could hear the rattle at idle. In neutral or in gear the rattle intensified with RPM, I put a screwdriver to my ear and the other end to the front timing cover and that was the only place I didn't hear it much at all. I let it idle and pulled one injector plug at a time, the noise did not change at all. I shut it down, started it back up and there was no rattle. I revved it up to about 4k a few times and still nothing. After the third or fourth time the rattle came roaring back. I repeated this process about 5 times and it seemed random, the rattle would be there at startup and sometimes I had to rev it a few times....very strange. Checking the sound at the valve covers it's more prominent on the passenger side, but I've been fooled before with sound traveling through metal so who knows.

This rattle is loud too. I've spun a rod bearing before and it didn't sound much like this, and wasn't this loud.

Whatever it is, it's not good, I think it's bottom end, but any opinions would be greatly appreciated :idea:

 

[Michaelslilgray]

Check your oil level... it sounds like after the system pumps it dry, the oil pump is starving and possibly grinding itself stupid? only other thing i could tell you is after you verify you have oil.. drain it and see what may happen to come out.

 

[99Venom]

Check your oil level... it sounds like after the system pumps it dry, the oil pump is starving and possibly grinding itself stupid? only other thing i could tell you is after you verify you have oil.. drain it and see what may happen to come out.

Well oil pressure looked fine, but after this noise I was anxious to see what might be in the oil so I changed it. I put a cloth in the drain pan and didn't see any shiny stuff at all, the oil looked and smelled perfectly normal.

After the oil was changed I started it up and for the first 4 or 5 revs, no rattle sound. On the 6th or so rev it came right back :fm:

 

[black4vcobra]

Well oil pressure looked fine, but after this noise I was anxious to see what might be in the oil so I changed it. I put a cloth in the drain pan and didn't see any shiny stuff at all, the oil looked and smelled perfectly normal.

After the oil was changed I started it up and for the first 4 or 5 revs, no rattle sound. On the 6th or so rev it came right back :fm:

You probably know this but don't pay attention to the stock oil pressure gauge, it is COMPLETELY useless.

If i had to venture a guess about the noise, it would be valvetrain related but it's impossible to pin down over the internet. A video of the noise would help some members identify it.

 

[99Venom]

You probably know this but don't pay attention to the stock oil pressure gauge, it is COMPLETELY useless.

If i had to venture a guess about the noise, it would be valvetrain related but it's impossible to pin down over the internet. A video of the noise would help some members identify it.

I will work on getting a video up. When I get home tonight I'm going to remove the serpentine belt and run it just to make sure this isn't some accessory noise that's bouncing all over the place. Should have thought of that yesterday.

 

[bossracer]

Sounds like mine. Remove your oil filter and cut it open. Mine was full of aluminum / silver colored stuff. Not copper flakes. Filter appears to have caught it all. Oil is ok.

Engine coming out next week. Still don't know what it is. But it is bad.

 

[9CobraVert8]

You should try pulling the valve covers before the motor. Maybe a valve got stuck open and a rocker popped off? And the rattling sound is that rocker bouncing off the cams?

 

[IUP99snake]

With the engine idling, disconnect each spark plug boot, one by one to see if the knock is associated with an individual cylinder.

An automotive stethoscope will really help you pin point the exact location of the knock.

 

[MrBrain]

sounds like a rod bearing, same happened on my gf's cougar. no noice at idle but at revs and during load it got noicier and noicier the more revs I gave it. funnily the crankshaft wasn't damaged at all, I dropped the oil pan and replaced the bearing and it have been fine ever since. Set me back around $50.

there was no problem identifying which rod it was, the slack was huge. I felt it by hand. The problem appeared out of the blue, I guess some surface gave up or something.

 

[Michaelslilgray]

With the engine idling, disconnect each spark plug boot, one by one to see if the knock is associated with an individual cylinder.

An automotive stethoscope will really help you pin point the exact location of the knock.

He pretty much did this by removing the injector pulse... its easier on the motor this way because gas doesnt accumulate in the cylinder while no spark occurs...

 

[99Venom]

This video shows how intermittent the rattle is. The first 40 seconds you really can't hear anything. Around 50 seconds it's louder than the engine.....

MVI_0559.mp4 Video by dw8649 | Photobucket

MVI_0560.mp4 Video by dw8649 | Photobucket

 

[IUP99snake]

He pretty much did this by removing the injector pulse... its easier on the motor this way because gas doesnt accumulate in the cylinder while no spark occurs...

....with inconclusive results....

I'm not guaranteeing that the results will be any more or less conclusive when removing the spark plug boots for each cylinder. But it is one more thing to try during the troubleshooting process.

The whole process of troubleshooting involves finding anything that can cause the problem to be more or less apparent, then controlling it and isolating it to the root cause.

I'm making this suggestion based on first hand experience. I was able to tell immediately using this method that a knocking sound was caused by a cracked piston skirt instead of a rod knock. It takes 5 minutes. It won't cause any damage. Once you are done, you know one way or another.

Regardless of whether the injectors or plugs were used to deactivate each cylinder.....Use the automotive stethoscope! Otherwise, you're just shooting in the dark. I swear, it's like a sixth sense!

 

[Michaelslilgray]

Just a honest question.... how old is the gas in this tank?

You may want to have someone else that had this happen to them.... did the 99's not have a tick TSB?

 

[99Venom]

The gas is about a week old, I'd been driving it every week up until this.

 

[MrBrain]

I'd still place my bets on a rod bearing, note how the noice increases during load when giving it a little bit of throttle. Probably not the thing anyone wants to hear, maybe it would be possible to drop the oil pan without removing the crossmemer entirely? With a dial indicator you'll see if there is slack in the rod without removing it, might even feel it by hand.

 

[99Venom]

It's definitely a bad bottom end noise, maybe not a rod bearing but possibly a crank bearing, the noise is so loud and deep. Since the noise seems to come and go, I'm curious if it's an oil delivery problem. I'm already in the process of hauling the engine out, just the last two top bellhousing bolts and I'll be ready to hoist it out and check the oil pan.

 

[MrBrain]

Is the mystery solved?

 

[99Venom]

Not yet, when I remove the motor this weekend is when I'll take off the oil pan and check the crank and rods.

 

[Drak]

I must of missed this thread, but mine sounds EXACTLY the same.
Nothing was inside the oil filter.

 

[RX1Cobra]

I know this is late advice but always run 7 qts of oil. Oil doesn't come close to touching the crank and gives you some breathing room for running low on oil. These motors are really sensitive to running low on oil and use some between changes. After an oil change check the oil every 500 miles with the motor warmed up and right after shutting it down fill it to the full mark on the dipstick. Done this for 12 years now with my car and still runs strong even with a blower on it.