Harbor Freight Tools, Sears, Walmart, any auto parts store or hardware store will have compression testers. Many auto parts stores rent or borrow tools too.
The idea of running the engine first is that pistons expand more in one direction when they warm up and that makes them fit the cylinders better. All you need to be concerned with is consistency. You don't want to test one cylinder while the engine is hot and the last one when it has cooled down. The last one is going to read lower than it normally would.
Block the throttle open to eliminate that air flow restriction. Connect a small battery charger during the test so the starter isn't cranking slower on the last cylinders. Now temperature and cranking speed will be the same. The actual values aren't that important. What is important is you want all the cylinders to be nearly equal. If just one is real low, a cylinder leakage test will identify the cause. Many auto parts stores will have that tester too. It's easiest to use a remote starter switch when you want to crank the engine. The eliminates the need to figure out how to turn off the injectors and ignition system. You can also bypass the starter relay or pop its cover off and squeeze the contact. Listen to the compression pulses and crank every cylinder for the same number of pulses.
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Thursday, March 14th, 2013 AT 6:40 AM