Before we start to diagnose a vehicle, we need to have a game plan — just like a coach or manager of a major league sports team. Your game plan needs to start with a route on where and how to proceed in diagnosing the problem at hand. We all have different ways to diagnose a problem vehicle, but there may be a better route to follow.
I base my procedure on what’s right and what’s wrong, just like the big box scope analyzers did in the past. The good thing about the old big box analyzers is that they forced us to start at the battery, starter, alternator, engine mechanical condition, emission gas readings, ignition and fuel. Remember: If you miss the basics, you miss the problem.
The relative compression test is a real timesaver. Some OEM scan tools, like the Ford IDS, incorporate the test right in the tool.
If we were going to diagnose a sagging roof, you would not install a new roof without checking the walls and the foundation first. Similarly, in diagnosing an engine performance problem, we need to start with the basics. This is why it’s so important that at least two OE scan tools have a test to make sure that the mechanical condition of the engine is good. The reason why Ford and Toyota install these tests on their scan tools is that they have seen too many parts thrown at a problem by their own technicians, with no solution or fix acheived. The root cause of the problem in many cases stemmed back to something basic, from a bad battery to a mechanical issue.
Many engines that we work on today have some form of variable valve timing. The use of the wrong oil can cause the variable valve timing system to portray a mechanical problem. The cam phasers will not be able to adjust to the proper settings if the wrong viscosity oil was used, due to improper oil flow. What I will attempt to do in this article is to provide you with a good game plan, along with the tools to use in diagnosing problem vehicles.
Where to Start
The first place to start is by interviewing the driver of the vehicle. A good Q&A session might lead you to looking into an area that you might have not checked without the information they provided.
The next step is to use the best tools you own — your brain, eyes, ears, nose and hands — to check out the problem. After a preliminary “look-see,” research the problem using your service information (SI) source, followed by investigating Technical Service Bulletins (TSBs) that may be related to the issue.
With so many variations on even the most routine system, you have to know the particulars of the system you are working on before you even pick up a wrench. Information on iATN, Identifix, ALLDATA, Mitchell, Autodata, MotoLogic or even Google can be very helpful with identification, if the vehicle you are working on needs a reflash or has a silver bullet problem. Remember, when looking at a silver bullet solution, always check and test the components and the system before replacing anything.