Hi I have a 97 850 and I developed a misfire in my #5 cylinder I did a compression check and it went to 40psi and that was it,but,the weird part is is that it held at that # for almost an hr till I released the pressure can anyone give me some advice on what the cause could be.

 

A compression gauge has a check valve so it will hold pressure indefinitely. It just measures peak compression. You need to do a cylinder leakage test to find where the leakage is.

 

Ok how hard is this and what do I need to accomplish this.

 

You need a compressor and a cylinder leakage test gauge set which should come with instructions. You pressurize the cylinder at TDC compression and listen for where the air escapes.