The valves don't produce anything. They open to let gas and air in, then close to seal it in to be burned. It sounds like you were probably told by your mechanic one cylinder is only producing 60 psi during a compression test. That tests the integrity of the intake valve, exhaust valve, piston rings, and cylinder head gasket and their ability to seal in that gas and air. 120 to as high as 180 pounds on some engines is normal. For your engine I would expect to see 120 to 150 pounds. 60 pounds suggests something isn't sealing properly and can cause a misfire that you can feel as rough running, and it can be detected by the Engine Computers on '96 and newer models. That can result in a fault code being set in memory and the Check Engine light turning on. In most cases the computer can even detect misfires that are too minor for you to notice. A different test called a cylinder leakage, or cylinder leak down test can identify which of those four things is causing the leakage.
Your engine has six cylinders so the compression test involves six measurements. Besides each one being in the normal range, it's important that they all be about the same. To have just one cylinder lower or higher than the rest suggests a defective part. If all readings are low but consistent, it suggests high0mileage engine wear.
Saturday, December 3rd, 2011 AT 10:21 PM