Low compression?

BESTSWJ

MEMBER
2012 AUDI A4
2WD
100,000 MILES

I bought a used car just 3 weeks ago. After 2 or 3 days of purchasing the car, car started shaking on driving. Once the car had sign of engine and stopped, was moving to mechanic by a tow truck. The mechanic changed 4 spark plugs and it was pretty good for a few days, however, it start shaking a bit. The mechanic said it would be a piston ring problem. When he scanned the car, the compression was low in second cylinder and the spark plug was with oil. I don't know about a car at all and I'm in panic now. Please give me some information about what I should do. Thank you.

2 Replies

KASEKENNY

MECHANIC
18,907 POSTS

This does sound like a possible compression issue but we need to check that with a gauge. You can't get compression by scanning the vehicle so we need to actually check the compression and see what it is. Here is a guide on how to do that:

https://www.2carpros.com/articles/how-to-test-engine-compression

Depending on what the readings are we can go to the next step. However, the other likely cause here is a vacuum leak.

Here is a guide on how to check for a vacuum leak:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let us know if they gave you the readings on the compression test if they did do one and we can go from there.

Lastly here is a guide on changing piston rings if we go that route:

https://www.2carpros.com/articles/replace-engine-piston-rings

Thanks