How to Check the Engine Health With A PICO Scope

Testing Engine health with the PICO automotive lab scope Auto Service Tech Training today for tomorrow's challenges www.autoservicetech.com Loss of engine compression doesn't have to be much to affect how the engine runs. Testing compression the old fashioned way can be time consuming on modern engine designs. There are other methods, using a Digital storage Oscilloscope (DSO), that are faster and just as effective. Let's take a look at a few, using the PLCO automotive scope... The first is a "relative compression" test, using starter current draw as the indicator of engine compression. To perform this test, disable the ignition and/or fuel system se the engine will not start. Then attach your high amp clamp to the battery cable and connect to your scope.... Tip: use the AC coupling function to see just the pattern. We don't really care what the total current is for this test... it takes more effort to turn over a healthy cylinder than it dose a weak one! Here's an example of "healthy" starter draw... we're measuring current required at a time base that allows us to see how much it takes pre cylinder. Compare a healthy pattern to this one... with one plug removed; there is no compression on cylinder #6. See the "flat" in the pattern? But remember, this is "relative" to the overall health of the engine. If all cylinders are weak, the pattern may look OK. But that's an unusual occurrence. And it only takes a few minutes to perform. In real world applications, this test can distinguish even small differences in engine compression. Another method uses a pressure transducer to measure actual pressure caused by cylinder compression. This one is the first look sensor. This tool has a lot of uses for engine diagnosis. You can find out more at AutoService Tech,com for now, though, let's focus on using it for checking relative compression first step is to insert the transducer in the tailpipe. On all these tests, you must disable the ignition and/or fuel system so the engine will not star. Here's a healthy pattern with the firs look sensor attached to the PLCO... and here's one showing a problem on this transverse V6... With the PICO, you can "synch" the pattern to a specific cylinder. Then use the firing order to ID exactly which cylinder needs a closer look... let's take a look at a 6 cylinder with a problem... obviously, a weak cylinder... but is it in the valve train or the piston/rings? Let's move the first look to the ail dipstick tube and measure pressure in the crankcase... why? Pressure pluses in the crankcase are caused by the pistons moving up and down. If they are uniform, then the rings and pistons are sealing just fine. The loss, then, has to be in the valvetrain... we've isolated the problem... and it only took a few minutes to do. Checking compression and then performing a leak down test would have taken a few hours... which method would you prefer if you were the paying customer? As a working tech, how much time would this method save you? We hope you enjoyed this short presentation... for more info on the PICO and first look sensor, please visit us at... Auto Service Tech training today for tomorrow's challenges www.autoservice.com Testing Engine Health with the PICO scope By Peter F. Meier