![]() ![]() This is one of the most overlooked tests to find the root cause of a misfire code, rough idle or an engine miss or a blown head gasket. So, if the compression value, for the specific cylinder you're testing did not go up (after you added oil to it), then this is a dead giveaway that you've got cylinder head valve damage. Here's why: If the cylinder head valves and their seats are worn out (or maybe even bent from a broken timing belt), no amount of engine oil is gonna help seal the compression in, in the cylinder. This confirms that the problem is in the cylinder head valves. If the problem were in the cylinder head valves, then the engine oil you just added wouldn't make a difference at all (on the compression value).ĬASE 2: The compression value stayed the same. Here's why: The engine oil helped the piston rings seal better, thus bringing up the compression value almost back to normal. This tells you that the piston compression rings are worn out and thus the problem is in the bottom end (block) of the engine in your GM 4.3L, 5.0L, or 5.7L equipped vehicle. The results you obtain from this second ‘Wet’ compression test will help you determine if the low compression you recorded in the ‘Dry’ compression test are caused by worn piston rings or worn cylinder head valves.ġ) The compression value will go up (from the one you recorded before).Ģ) The compression value will stay the same.ĬASE 1: The compression value shot up. This involves adding a few drops (2 tablespoons) of engine oil to the cylinders with the low engine compression result and repeating the compression test. So, you've found the ‘dead’ cylinder or cylinders, what next? The next step is to do a ‘Wet’ compression test and find out if the low compression value (or 0 compression value you got) is due to bad cylinder head valves or bad piston compression rings. For this step, go to: TEST 2: Wet 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, so that this calculation can make more sense to you, let's say that my 4.3L C1500 Pick Up (or Astro or Blazer, etc.) gave me 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: ). If one or more cylinders have compression value lower than 15% of the highest compression value, your GM 4.3L (or 5.0L, 5.7L) equipped vehicle will run rough or cause a misfire code to set and turn on the check engine light.įiguring this 15% difference isn't hard, you can easily figure out in one of two ways: You can calculate this 15% difference with pen and paper or you can use my low compression calculator. The idea behind the engine compression test (in the case of a misfire condition or rough idle condition) is to find out if any one engine cylinder is not contributing 100% of its power to the overall engine output. Interpreting The Results Of The Engine Compression Test
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |