Low compression on 5 and 6?

**AndyB** · 06-06-2016 07:08 AM

What's up all, 2005 s4 78k. Factory guides/adjusters. Just got my car compression/leak down tested. Cyl 5 and 6 have a 10% leak down, compression numbers 140. All other cylinders are at 168-172. Bringing her to excelerate soon to let them take a look. Trying to come up with some reasons for the low numbers on 5-6? Can it be worn guides or adjusters? They also boroscoped the cylinders and told me they all look mint. Any help is appreciated. Thanks for looking.

**AndyB** · 06-06-2016 07:54 AM

Oil consumption is around 1 qt every 2k

**Sphawkins007** · 06-06-2016 09:51 AM

Why did you run the car through those tests? Was it acting up in anyway like misfires etc. 1qt every 2k isn't bad.

**AndyB** · 06-06-2016 10:08 AM

Took it into dealer for a slight noise behind the motor, which I beleive is the timing. It did have a random misfire. They recommended the test so I proceeded.

**JimmyBones** · 06-06-2016 11:55 AM

Typically cylinders 5 and 6 are the two that have issues with these engines. They tend to get scored, lose compression, and thus gain more cylinder leakage first. Espicially cylinder 6. All the BHF engines that I have tested with bad cylinders were the worst on cylinder 6.

That really isn't bad cylinder leakage at 10% though.

Have you ever replaced your PCV valve?
Do you see any blue smoke at cold start up or during deceleration on the highway?

**AndyB** · 06-06-2016 01:40 PM

Never replaced the PCV valve, I don't have any blue smoke on cold start or deceleration, never seen any signs of burned oil from this car. I did start smelling a burnt plastic/electrical smell recently but I think it may be coming from my aftermarket radio as the head unit has been getting extremely hot recently for some reason.

**JimmyBones** · 06-06-2016 06:42 PM

Do you still have the stock cats? They can burn off a lot of the oil, especially if you do a lot of highway driving. You have to remember that the oil is going somewhere.