Let's take a look at what your test results mean:ĬASE 1: The compression value shot up. If the compression value does not increase, then we can conclude that the low compression problem is due to the cylinder having worn/damaged intake or exhaust valves.ġ.) The compression value will go up (from the one you recorded before).Ģ.) The compression value will stay the same. If the compression value shoots up, then we can conclude that the low or 0 PSI compression problem is due to the cylinder having worn/damaged piston rings. We can do a 'wet' engine compression test to find out.Ī wet compression test simply involves adding a small amount of engine oil to the cylinder with low or 0 PSI compression and then retesting its compression. To find out which is the case, we don't need to take the engine apart (just yet). The affected cylinder's intake or exhaust valves are severely worn or damaged.The affected cylinder's piston rings are worn or damaged.TEST 2: ‘Wet’ Engine Compression TestĪ low or 0 psi compression value is usually the result of one of two things: For this step, go to: TEST 2: ‘Wet’ Engine Compression Test. Once you've found the 'dead' cylinder, the next step is to find out what's causing the low compression value. Of course, you'll need to use the highest compression value you got and not the one in the example. To find out if the lowest compression value you got from your engine compression test is within a good range, you'll need to do the same calculation. Since cylinder #2 is only producing 95 PSI, I can now conclude that it's 'dead' and causing a misfire. Any cylinder with this compression (or lower) value will misfire. STEP 2: 26.25 = 26 (rounded to nearest one).My next step is to do the following calculation: Now, let me give you a more specific example: Let's say that I got the following compression readings: Cylinder ANSWER: The result of this subtraction is the lowest possible compression value any cylinder can have.STEP 3: Subtract the result (the number that was rounded) from the highest compression value.STEP 2: Round the result to the nearest one (for example: 25.6 would become 26).STEP 1: Multiply the highest compression value by 0.15 (this is the decimal value of 15%).If you want to manually calculate the 15% difference, here's what you'll need to do: You can find the low compression calculator here: Online Low Engine Compression Calculator (at: ). You can do this (figuring out the 15%) in one of two ways: You can calculate this 15% difference with pen and paper or you can use my low compression calculator. To find out, we need to figure out if the low compression values are lower than 15% of the highest compression value you got. The cool thing is that we can easily find out if the low compression values are causing an engine performance problem or not. If the variation is small enough, you're not going to notice any type of engine performance problem.īut if the variation is too big, then you're going to see a misfire problem or a rough idle problem. Compression Testing of Internal Combustion Engines - Direct Compression and Differential Compression Testing
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