compression test made weird noise

[mccurdy]

So i just got my car back from the shady dealership. They said my compression was '45' on cylinder 3, so i did the test on my own after i warmed up the car and charged the battery.

I got 180 180 150 180.

However, when i was doing the compression test, when i was cranking it at WOT, i heard this weird loud repetative tapping noise. It sounded like a loud 'DINK' sound. Almost like hitting 2 hard metal objects together. It was a definately noticeable noise.

What could it have been?

 

[Jeff99GS]

The only thing i can think of would be to remove your Inspection plate and check your Flywheel...I had Mine loosen up on my jeep and it sounded like that.
I just took off the inspection plate and tighten the bolts with a Racheting wrench.

 

[mccurdy]

but it doesn't do it on all cylinders i test. this time it did it only on 4, 1, and 2, not 3

last time it did it on 3 and 4

 

[mccurdy]

doesn't anyone know what I am talking about?

 

[crimsondragon]

You're saying that it makes a dink when you first tested it on cylinder 3 & 4. The second time you tested it, it made a dink on 4, 1, and 2. Chances are it's randomized and has nothing to do with which cylinder. Can you pinpoint the sound? Don't want to scare you but it could be rod knock.

 

[romeen]

When the high pressure air fills the tubing it momentarily causes it to become stiff and straighten out. So the gauge at the end of it jumps up off the valve cover or whatever you have it resting on. Then the hose loses the pressure, goes limp (I know this sounds Freudian) and the gauge comes down and hits the VC or something making kind of a hollow popping sound. Obviously if it misses the VC, no noise.

At least that's what it turned out to be for me. Have someone watch the tester when you crank it or try to peak out from under the edge of the open hood to confirm.

 

[mccurdy]

i had my roommate holding the tester while i cranked it, so I don't think its that. But i don't know what else it would be besides air escaping somewhere. That noise just bothered me.

 

[crimsondragon]

When you turn the car on, can you hear anything?

 

[mccurdy]

the actual car with everything connected? Nope. just normal engine sound

it was only during the compression test. I guess i just want to make sure i didn't damage anythign when doing the test. I've heard of compression testers being too 'long' and causing damage internally. This one didnt appear so though, as it was shorter in length than the spark plug itself.

 

[DougR]

One method I use to find noises in my engines is to use a 2 foot section of a wood broom handle...

You touch the various points on the engine that might be making the noises. While cupping your hand around your ear and the other end of the wooden handle...

The noises transfer up the wood and into your ear.
You would be SO shocked at how mutch you can hear internally in your engine this way...
Just be careful....

 

[Big Woo]

You may just be hearing the valves shut in the cylinders not being tested since you have the spark plugs out. They are metal and so are the seats they seal on.