Diagnostic Procedures

Diagnostic procedures are the methods involved in finding the root of a problem. You drill through a list of tests and potential issues, eliminating them until you find the problem. In my case, the problem is that my truck won't start. Lets get into my methods and see how I find problems.

Knowing what a piece of equipment needs in order to function properly is key to making a diagnosis. In my case, an engine needs 3 things to function: air, fuel, and spark (or compression, in a diesel). My engine will crank, but won't actually start. This means that I'm missing at least one of those critical elements.

Air is fairly straightforward. My filter is in decent shape, my turbo is functioning correctly, so air is getting into the engine.

Compression was my first thought. I didn't have any indicators of a catastrophic mechanical failure, so I look to my electrical system, with the idea that insufficient electrical current won't turn the engine with enough energy to get ignition. With 2 batteries, there may be enough power to turn the engine, but not with the force needed to actually ignite the fuel/air mix. Both batteries have 12.7 volts and test good on the machine at my local parts house. The alternator likewise tests good. Volts are present, so the next step is checking that they're actually getting to the parts that need them.

Using my electrical multimeter, I checked for continuity on all my fuses. I found one that was burned out, but it's unrelated to any of my engine components. (It is for lights on one of my trailer plugs.) I also tested the relays that control my engine functions. The easiest way to do this is to use another relay with the same part number. My fuel pump relay is the same as the relay for my air conditioning, and the relay for my daytime running lights. My ignition and starter relays are the same as the relay for my rear window defroster. Changing out these relays will tell you if a relay is malfunctioning. In my case, swapping relays did nothing.

This virtually eliminates anything in my electrical system as the point of failure. This leads us to fuel as a culprit. Chasing fuel leaks requires special knowledge and tools. If you're not equipped, this is the time when calling a mechanic can save you hours of time and headaches. If you have the tools and skills, I don't have to explain this part of the process to you.

The principle applies to any piece of equipment. The same idea of listing possible causes and eliminating them works for malfunctioning lights, plumbing issues, or any other problem you might face. Notice that I did the quick, easy, and free checks first. The more you can eliminate in short time and for zero cost, the better. It takes a bit of practice to brainstorm possible causes, so don't be afraid to call friends who have experience with whatever you're fixing. I still find myself making that call from time to time.

A bit of logic and some testing helps you find the root of your problems. This saves you time at a mechanic or sometimes that bill itself.

Lokidude