Car with mystery noise

[Raduque]

Will it knock at idle, or will it only knock when revved up?

Edit: Video of the mystery noise: http://www.youtube.com/watch?v=E_h0ULvavEI

Crappy cellphone camera, sorry.

 

[exdeath]

It will knock all the time, and get louder and faster with revs.

Pulling the plug wire on the suspected cylinder will quiet it.

 

[Raduque]

How about a noise that's definitely a mechanical "one part hitting another" noise that's very loud and only happens above ~1500rpm?

 

[TehMac]

Originally posted by: exdeath
It will knock all the time, and get louder and faster with revs.

Pulling the plug wire on the suspected cylinder will quiet it.

Won't you lose that cylinder's output though?

 

[brblx]

hence the term 'cylinder cutout test'...

rad- is the noise any different based on engine temp?

 

[Squisher]

Originally posted by: TehMac

Originally posted by: exdeath
It will knock all the time, and get louder and faster with revs.

Pulling the plug wire on the suspected cylinder will quiet it.

Won't you lose that cylinder's output though?

This is just to locate which cylinder is knocking, not a solution to the problem.

The solution involves a little more work.

 

[Raduque]

Originally posted by: brblx
hence the term 'cylinder cutout test'...

rad- is the noise any different based on engine temp?

Noise is sometimes not there when engine is cold. NEVER makes the noise at idle, and ONLY above 1500rpm. It sounds to both myself and my dad that it's coming from the top end at the front of the motor. Car is a 91 Stealth ES DOHC V6.

It also runs pretty badly and doesn't seem to have much power, especially in first (ATX). I need to get an analog voltmeter to read the codes.

Edit: The noise definitely speeds up with engine speed. My dad thinks the valves are floating due to the timing being messed up.

Edit 2: A guy on a Stealth/3KGT forum says the noise is the piston slapping the bottom of the head, because it spun a rod bearing. But then, he also said you don't hear rod knock at idle. If it spun a rod bearing, what kind of oil pressure would I be seeing?

 

[Raduque]

.

 

[lsd]

Oil pressure would be low. Have you drained the oil and checked for bronze or copper colored flakes?
In my experience a spun bearing makes a hollow knocking sound.

 

[Raduque]

Oil pressure looks good on the gauge. Gonna pull the pan in the next couple days and check the rods for play.

I'm hoping it's not a spun bearing. I reeeeealy don't feel like pulling the whole motor for a rebuild.

 

[mayonnaise]

Could be a severe case of lifter tick? 😛 I know the cars suffer from it not sure if it can go to such an extent though.

 

[Raduque]

Well, it's got the lifter tick these cars are known for on top of the other clacking noise.

So I dunno.

 

[LTC8K6]

Timing belt tensioner?

 

[MiataNC]

Originally posted by: LTC8K6
Timing belt tensioner?

^This seems likely

Have you hit it with a timing light? Does the timing mark jump around when you rev it under the light?

 

[brblx]

i would definitely check the timing belt. i've seen those V6's still running with the tensioner literally about to fall off.

that doesn't sound like a bottom end noise, but it's hard to tell with the quality and brevity of the video. rod knocks (and valvetrain noises) tend to be more regular and rhythmic, your noise sounds different.

 

[exdeath]

Originally posted by: TehMac

Originally posted by: exdeath
It will knock all the time, and get louder and faster with revs.

Pulling the plug wire on the suspected cylinder will quiet it.

Won't you lose that cylinder's output though?

If that even made the noise go away and confirmed the rod knock, being down a cylinder is the least of your problems.

 

[Raduque]

Originally posted by: brblx
i would definitely check the timing belt. i've seen those V6's still running with the tensioner literally about to fall off.

Originally posted by: MiataNC

Originally posted by: LTC8K6
Timing belt tensioner?

^This seems likely

Have you hit it with a timing light? Does the timing mark jump around when you rev it under the light?

Would a failing belt tensioner keep good pressure on the belt? It seems to have good tension every time I check the belt.

I haven't used a timing light on it, unfortunately, don't have one.