{"id":8660,"date":"2017-04-14T17:41:33","date_gmt":"2017-04-15T01:41:33","guid":{"rendered":"https:\/\/corksport.com\/blog\/?p=8660"},"modified":"2024-02-19T13:11:17","modified_gmt":"2024-02-19T21:11:17","slug":"how-to-diagnose-a-misfire","status":"publish","type":"post","link":"https:\/\/corksport.com\/blog\/how-to-diagnose-a-misfire\/","title":{"rendered":"How to Diagnose A Misfire"},"content":{"rendered":"\n
\"Mazdaspeed<\/figure>\n\n\n\n

It\u2019s safe to say that most of us who are into modifying cars have seen this delightful CEL pop up on our dash. The P0300 (random\/multiple cylinder misfire) can be one of the most annoying codes when it comes to drivability.<\/p>\n\n\n

\n
\"Diagnosing<\/figure><\/div>\n\n\n

Sometimes a P0300 is very simple to sort out. Other times, it may take all day to track down. That said, here\u2019s a user-friendly guide for those modders who are learning and would like to figure out the problem themselves.<\/p>\n\n\n\n

Break down of combustion<\/h2>\n\n\n\n

In order to properly function, an internal combustion engine has four basic requirements:<\/p>\n\n\n\n

    \n
  1. Air (O2)<\/li>\n\n\n\n
  2. Fuel<\/li>\n\n\n\n
  3. Compression<\/li>\n\n\n\n
  4. Spark (or ignition)<\/li>\n<\/ol>\n\n\n\n

    Loss of one or more of these will cause a misfire. Understanding these requirements will better allow you to diagnose a problem and make an educated decision about what the problem might be \u2014 rather than just throwing parts at the car.<\/p>\n\n\n\n

    Types of misfire codes<\/h2>\n\n\n\n

    There are two types of misfire codes. The first, P0300, means the misfire is happening on more than one cylinder (and\/or happening randomly) and the powertrain control module (PCM) isn\u2019t able to find where the misfire is originating from. The other type of misfire code is anything above P0300: P0301, P0302, etc. The last digit indicates the cylinder number that the misfire is occurring on. This means that there is a clear pattern for a misfire occurring on that specific cylinder. These codes are much nicer \u2014 and simplify the diagnosis of your misfire without a doubt.<\/p>\n\n\n

    \n
    \"Misfires<\/figure><\/div>\n\n\n

    Diagnose This First<\/h2>\n\n\n\n

    Let\u2019s go ahead and start with the easier type of code.<\/p>\n\n\n\n

    One day, you\u2019re driving down the road. The car feels a little bit rougher than normal, then your CEL comes on, and the P0304 code comes up on the Accessport\/Scan Tool<\/a>. This means that cylinder number four is having a misfire. Here are a couple of steps to figuring out the culprit.<\/p>\n\n\n\n

    We already know what the four basic combustion requirements. Typically, the easiest and first thing to check would be your ignition system. So we\u2019ll start the diagnosis with the spark plugs and coil packs.<\/p>\n\n\n\n

      \n
    1. Since the code was for the number four sensor, you\u2019ll start on that cylinder. Number one is on the side where your drive belts are and, in this case, they progress from left to right.<\/li>\n\n\n\n
    2. There are two components that could cause an ignition failure, assuming that your PCM is in good working order. These components would be your spark plugs and coil packs. It\u2019s as simple as playing some musical chairs with them to see which one is the culprit.<\/li>\n\n\n\n
    3. Take your number four spark plug and swap it over to your number one cylinder. Now take your number four coil pack and put it on your number three cylinder.<\/li>\n\n\n\n
    4. If the misfire jumps to the number one cylinder, you know it\u2019s your plug. If it follows to number three, then we know it\u2019s your coil pack. If it stays on number four, then we\u2019ve eliminated the ignition system and can proceed to the next step.<\/li>\n<\/ol>\n\n\n
      \n
      \"\"<\/figure><\/div>\n\n\n

      Now your remaining options are either a problem with your fueling or a problem with the compression of your specific cylinder. To check this, perform a compression and a leak down test to verify the health of the motor, which will give you some peace of mind. However, if you find that the compression is low, or your leak down was excessive, you\u2019ll have your answer right there. Typically, low compression and excessive leak down can be a result of valves not seating correctly, warped cylinder walls, bad piston rings, or other similar issues.<\/p>\n\n\n\n

      If you\u2019ve done these two tests and everything has come back good, then we can cross that off the list (phew!) and move on to what\u2019s next!<\/p>\n\n\n

      \n
      \"\"<\/figure><\/div>\n\n
      \n
      \"\"<\/figure><\/div>\n\n\n

      Misfire Due to Fuel Pressure<\/h2>\n\n\n\n

      If you have an AccessPort or readily available scan tool, checking your fuel pressure in regard to a misfire will be very easy. If your car is not direct injected you probably won\u2019t be able to monitor it on your electronic control unit (ECU). So, you\u2019ll more than likely need to hook up an inline fuel gauge to make sure you\u2019re getting adequate pressure.<\/p>\n\n\n\n

      In this case, with our Mazdaspeed3, we\u2019re able to see the PSI of our high-pressure system which makes diagnostics on this easier. Pressure, at idle, should be somewhere in the range of 400+ PSI for this vehicle. If you\u2019re seeing a PSI under 100, then the pump is not creating any pressure and it\u2019s just flowing through from the in-tank pump. If you\u2019re seeing a PSI in the 200s, then your pressure relief valve may need to be replaced.<\/p>\n\n\n\n

      Monitoring your fuel pressure can give you lots of good information that can potentially tell you what\u2019s causing a misfire. These issues aren\u2019t as common, but they do still happen. If the pressures and fuel pump check out, then you\u2019re on to the next step!<\/p>\n\n\n\n

      Misfire Due to Injector Seals<\/h2>\n\n\n\n
      \"\"<\/figure>\n\n\n\n

      Injector seals<\/a> are a very important part that often gets overlooked. On higher mileage cars, or cars creating more power, the injector seals are a contributor to misfires and loss of performance.<\/p>\n\n\n

      \n
      \"\"<\/figure><\/div>\n\n\n

      As you can see in the image, the upgraded injector seal on the left has a much more rigid design. These seals have a proven design that, believe it or not, don\u2019t have a single reported failure! You can find those injector seals here<\/a>. As well as the fuel injector puller<\/a>!<\/p>\n\n\n\n

      While you\u2019re working on this area, it\u2019s a good time to clean out any carbon build-up in the ports and on the tips of the injectors. Carbon that builds up on the tips can keep the fuel from properly atomizing, so clean them as best you can. Make sure the seals, as well as the seats for the seals, are very clean so they can adequately seal.<\/p>\n\n\n\n

      The chance of an injector failing is very small on this platform, but it\u2019s still possible. If you have a cylinder-specific misfire code, and you\u2019ve eliminated all other possibilities, it\u2019s time for a new injector.<\/p>\n\n\n\n

      \n