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I recently had the pleasure of being involved in a challenging situation. The customer had a mishap with their vehicle where it hit a chunk of ice in the road. The ice did substantial damage causing the need for the engine to be replaced. The engine was replaced at another shop, and they were unable to get the vehicle running correctly. After several attempts and spending too much money, I was asked to take on the task.
The other repair shop had multiple miss fires and, of course, multiple diagnostic trouble codes were sent to the control module. When they read the codes they determined that the fuel injectors also needed replacement. The injectors were replaced with non-OE injectors and the code was still present. The codes could be cleared but after a few minutes of driving they returned. This is where the skill of understanding the trouble codes and having the correct equipment comes into play. When miss fire codes appear it can be for several different reasons and cause other trouble codes to appear. One code that can appear is a low-voltage code because the engine isnāt spinning the alternator fast enough to produce the necessary voltage. Another code that can appear are a brake modulator code. This is due to low voltage being supplied to the brake modulator.
Miss fires usually happen for 3 main reasons. First is an electrical problem between the coil and spark plugs. A spark plug could be fowled or damaged, a coil could be bad, or the plug wire or boot can be damaged causing electricity to escape (arc) before reaching the spark plug. There could be a miss fire from a fuel injector putting too much fuel into the cylinder, drowning out the spark from the spark plug. Otherwise known as a rich fuel condition from the fuel injector. The last, and most overlooked, is referred to as a Lean fuel condition. This happens when more air is coming into the combustion chamber than fuel. This is generally not a problem with the injectors. More often than not it is a sign of a vacuum leak. It is very important to know that when diagnostic trouble codes appear, the code only shows what system is causing the code and not what is causing the problem.
In the case of our customerās vehicle, we noted the miss fire trouble code. We swapped around coils and spark plugs to see if the miss fire would change cylinders. No change happened there. Next, we ran a live data list to see if we had a rich or lean fuel condition. Here is where we were able to determine what was happening. The data list revealed a lean fuel condition allowing our technician to find where 1 vacuum hose, on the back of the engine, was never connected. The technician also found where the PCV (Positive Crankcase Ventilation) valve hose was never connected. Within a few minutes of completing the diagnosis, the vehicle was fixed and running as it should. We also did not have to spend unneeded labor and parts to fix it.
Hooking up a computer and pulling codes is only the starting place of diagnosis. Having the right equipment, knowledge, and experience makes all the difference between a positive outcome and an unpleasant situation. Even the most experienced technicians will forget something when tackling a bigger job. However, catching mistakes and fixing them before situations escalate separates technicians from parts replacers.
I know for sure that having a competent mechanic who you know is gonna treat you right is an invaluable resource. Good on you š