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A runing compression check would have nailed it, the reason it did no on a crank"in check izz the compession sealed the valves and only needed to have enuff spring tension to hold"em till the compression took over. The volumetric efficiency test or running compression test is a very good test to use any time you have a engine miss that can"t be traced to ignition or other basic systems or when there is a lack of power. Step 1. Perform a cranking compression test with all plugs out and the throttle open. Step 2. Record your cranking compression readings. Make sure the charging system was up to snuff so all cylinders were tested under the same conditions. Step 3. Install all plugs but one. Install a standard compression gauge in the remaining hole with the shrader valve in place. Step 4. Start the engine. Yes, it will run but will be missing on the cylinder with the compression gauge. Burp the gauge and allow the reading to stabilize. It will be bouncing around at about 50 to 60 psi. (the throttle is causing a restriction and the piston is moving fast compared to cranking speed causing only a partial fill of the combustion chamber). Step 5. Snap the throttle wide open and return to idle. The gauge will hold at the peak reading. This reading is higher than idle because the peak comes at the instant the throttle restriction is removed and the piston speed is relatively slow. Step 6. Record your readings for running snap compression for all cylinders. The running compression reading should be approx. 80% of cranking compression. (example: cranking compression = 150psi running compression should = about 120psi) If your running reading is below 80% of cranking compression, the intake system is causing a restriction. If the running reading is above 80% of cranking compression, the exhaust system is causing a restriction. If the problem is in one cylinder you either have a problem with a worn camshaft, broken spring/rocker, carbon build up, etc. If the problem is on all cylinders look for a restricted intake system or clogged cat/muffler. The 80% spec is a ballpark spec and should be used as such. Remember that cranking compression is a measure of cylinder seal while running compression is a measure of volumetric efficiency or the cylinders ability to draw the air/fuel mixture into the combustion chamber Also what a cranking compression test tells ya and remember its only a place to start, if you have problems you will need to do a cylinder leak down test to trace the leakage. the first stroke of the compression (assuming it is not starting on an open
valve condition) indicates valve sealing capabilities. Generally, it should
be about 2/3 of the total compression. The first stroke is the valve
sealing, and each stroke afterwards, whether you do 4 total, 5 total, or
absolute total compression
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