Why would 3 cylinders have higher than normal compression results?

[Easily Distracted]

I'm chasing down a problem that started this morning and in doing so, did a compression check on my engine. Cylinder 6, 5 and 4 all read about 155# which is what bently says is at the high range of normal.

For some reason I got around 175# on cylinders 3, 2 and 1. What could cause this?

On my last compression check about 30k miles ago, none of the cylinders read above 155#.

[Easily Distracted]

Bump for Sunday morning.

[e30_kid89]

Maybe those cylinders with higher compression results have excessive carbon build up, causing the CR to creep up.

[matt]

More likely a leaking head gasket or misadjusted valves on the low cylinders.

[Easily Distracted]

Maybe those cylinders with higher compression results have excessive carbon build up, causing the CR to creep up.

There should be very little carbon. I have hot soaked the combustion chambers with Ventil Sauber a few times over the years and just recently did the same with SeaFoam and had almost no smoke result. The very first treatment smoked like crazy a couple of years ago, but since then has needed very little cleaning. The #6 cylinder would be the one I suspect to have carbon the most because I know the valve guide seal is starting to leak a little, but that one is in the correct range.

More likely a leaking head gasket or misadjusted valves on the low cylinders.

The low cylinders are at the high end of what the Bently says is normal. The high ones are above normal.

[Easily Distracted]

Update. I just fixed an air leak in the valve cover gasket that was causing a lean condition. Maybe there was some strangeness going on in those cylinders because of the recent poor combustion. I will recheck after cleaning and running a litttle longer. Engine is running smooth and strong right now. Thanks for your input e30 kid89 and Matt.

[Mossman]

I would guess your cheapo gauge cannot be trusted within 10% and not wonder why it's higher, but why all of your cylinders arent within 5% or so. If it's running good I wouldn't sweat it either way, but a little birdy told me a vacuum leak won't make your compression higher, if you can prove otherwise I will induce a monster leak first thing tomorrow morning.

[Easily Distracted]

Cylinders within 5% was myfirst concern otherwise I wouldn't give a crap. Wasn't saying a vacuum leak raises compression. I thought it might have screwed up the mixture causing bad combustion and possible quick carbon/crap buildup. I read carbon deposits can raise combustion (must be true. I read it on the intraweb). Another thought was - with a leaking VC gasket, some oil might have dripped into the spark plug channels and into the combustion chamber of those cylinders when the plugs were removed, affecting the test. Either way, still running good and will recheck soon with another gauge incase my "cheapo gauge cannot be trusted".