Misfire DTC problems
Misfire term is usually badly defined and interpreted. The literal translation would be the lack of fire, which is not so bad explanation. However, this term refers to the malfunctioning of one or more cylinders, either due to lack of spark or fuel. When such codes appear, we shall read Random Misfire or Misfire of 2 78 nd cylinder, or some other number.
In the first case we have a problem with sudden malfunctioning of several cylinders without any order, or, we would say, randomly. In the second case, malfunctioning refers to the cylinder number 2, or some other numbered cylinder. This means, that the ECU has detected discontinuity of functioning on one or more cylinders defined by numbers. Random Misfire usually occurs due to the bad fuel or some impurities in it.
In the first case we have a problem with sudden malfunctioning of several cylinders without any order, or, we would say, randomly. In the second case, malfunctioning refers to the cylinder number 2, or some other numbered cylinder. This means, that the ECU has detected discontinuity of functioning on one or more cylinders defined by numbers. Random Misfire usually occurs due to the bad fuel or some impurities in it.
The cause may also be due to failure of the vacuum hoses or worn seals. Disrupted ignition timing and carbonized injectors are also often the cause of these errors. Worn out distributor cap (on engines with distributor) and spark plugs cables covered with dirt and grease can also cause disruption of cylinders without any order.
When a Misfire DTC occurs with cylinder number, then we know that we have to focus on that cylinder and look for the cause of firing interruption. To solve such problem, theoretical knowledge and experience will be of great necessity. Most often, we firstly check the condition of spark plugs.
Having in mind how any mechanic is familiar with problems caused by spark plugs, cables and pipes; let’s talk about misfiring of cylinders in pairs. Vehicles which have two ignition coils, or one for two cylinders, and the error refers to a pair of cylinders that are connected to the one of them, we can doubt its validity.
When a Misfire DTC occurs with cylinder number, then we know that we have to focus on that cylinder and look for the cause of firing interruption. To solve such problem, theoretical knowledge and experience will be of great necessity. Most often, we firstly check the condition of spark plugs.
Having in mind how any mechanic is familiar with problems caused by spark plugs, cables and pipes; let’s talk about misfiring of cylinders in pairs. Vehicles which have two ignition coils, or one for two cylinders, and the error refers to a pair of cylinders that are connected to the one of them, we can doubt its validity.
On vehicles with a separate coil for each cylinder, we can apply the test by exchanging the coils from one cylinder to another, and see if the error will again refer to the same cylinder, or the one on which we set up a coil of doubtful validity. The same test can be applied in the first case too, if we have identical connectors. Such verification will certainly determine, whether we have defective coil, or the problem lies elsewhere.
The second problem usually lies in the injectors. If we suspect the injector, it is recommended to replace it with one from another cylinder.
The test is identical to previous one with coils. If an error occurs with the number of cylinder where we installed the injector with dubious validity, we can conclude with certainty that injector is faulty. However, if the error re- peats with the same cylinder number as before, the problem lies elsewhere. Certainly, if we swapped coils ad injectors between cylinders and found nothing wrong with them, but DTC still exists on the same cylinder, we should look for the problem in the worn vacuum seals or, furthermore, bad piston rings and valve seals, which will cause accumulation of oil deposits on the spark plugs.
The second problem usually lies in the injectors. If we suspect the injector, it is recommended to replace it with one from another cylinder.
The test is identical to previous one with coils. If an error occurs with the number of cylinder where we installed the injector with dubious validity, we can conclude with certainty that injector is faulty. However, if the error re- peats with the same cylinder number as before, the problem lies elsewhere. Certainly, if we swapped coils ad injectors between cylinders and found nothing wrong with them, but DTC still exists on the same cylinder, we should look for the problem in the worn vacuum seals or, furthermore, bad piston rings and valve seals, which will cause accumulation of oil deposits on the spark plugs.
In practice, the occurrence of such DTCs is usually caused by deposit of carbon on the injectors where occasionally proper injection fails. It is not uncommon that mentioned checks are performed, and,
in those worse cases, very costly replacements of injector, spark plugs cables and coils are done, without any results. Just for this reason, these tests are recommended. Satisfied with all performed tests which have showed the correctness of all electronic elements and mechanical parts, injectors cleaning is all what is left do be done. Do we have to do this job before or after these tests, it is difficult to say.
Those a little more experienced will be lead by vehicles mileage and bring the right decision. Certainly, if we work on the vehicle with mileage of several hundred thousand miles, we shall immediately suspect a carbon deposit on the injectors, while on
in those worse cases, very costly replacements of injector, spark plugs cables and coils are done, without any results. Just for this reason, these tests are recommended. Satisfied with all performed tests which have showed the correctness of all electronic elements and mechanical parts, injectors cleaning is all what is left do be done. Do we have to do this job before or after these tests, it is difficult to say.
Those a little more experienced will be lead by vehicles mileage and bring the right decision. Certainly, if we work on the vehicle with mileage of several hundred thousand miles, we shall immediately suspect a carbon deposit on the injectors, while on
those with low mileage we shall first perform described tests. Injectors contaminated with various sediment, are the most common cause of hesitation during the acceleration and uneven engine idling, including Misfire. On the photographs we can see the irregular fuel injection due to deposits of carbon and other materials. Proper injection is shown on comparative photo. So, let's say something about the possibility of cleaning the injectors.
The simplest way is pouring special chemical product into the fuel tank, which will pass through the injectors and dissolve the accumulated material. Such a procedure is quite effective, if there is a milder form of deposits. In more serious cases of deposited carbon and other impurities, injectors have to be removed from the intake manifold and cleaned by machine. If we want to save some money, a similar procedure can be done by purchasing a spray, and clean the injectors under the pressure with its content. The photo shows this process with the help of battery which activated the injector solenoid and opened flow.
The simplest way is pouring special chemical product into the fuel tank, which will pass through the injectors and dissolve the accumulated material. Such a procedure is quite effective, if there is a milder form of deposits. In more serious cases of deposited carbon and other impurities, injectors have to be removed from the intake manifold and cleaned by machine. If we want to save some money, a similar procedure can be done by purchasing a spray, and clean the injectors under the pressure with its content. The photo shows this process with the help of battery which activated the injector solenoid and opened flow.
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Some sprays offered on the market, allow us to empty its content directly trough the throttle, previously removing the air filter. Such sprays will clean the outer surface of injectors, deposits on valves, pistons and cylinder compression area. But if we want a proper injectors cleaning without risk of failure during the cleaning, they should be connected to the cleaning machine.
Using professional equipment to clean injectors, allows us to have the flow of solvent trough the injector until we are satisfied with proper fuel injection. During the cleaning, these machines allow us to measure the amount and equalization of the fuel flow through the each injector. On the next photo we see a typical injectors cleaning machine. Unlike the smaller available machines, this one can clean and testup to eight injectors at once. In the measuring cups below the injector, we measure the quantity of injected fuel, which ideally should be identical in all eight cups.
Using professional equipment to clean injectors, allows us to have the flow of solvent trough the injector until we are satisfied with proper fuel injection. During the cleaning, these machines allow us to measure the amount and equalization of the fuel flow through the each injector. On the next photo we see a typical injectors cleaning machine. Unlike the smaller available machines, this one can clean and testup to eight injectors at once. In the measuring cups below the injector, we measure the quantity of injected fuel, which ideally should be identical in all eight cups.
