Troubleshooting- a sound diagnostic approach
This article outlines a methodical approach to identifying, diagnosing and repairing a vehicle. The benefits to this approach is less time spent between first recognizing the problem and making the repair.
 Info needed to help diagnose a problem
It's very important to give as much info as you can about the vehicle and engine. Choose any/all that apply from the following list (can be cut/pasted to a thread):
Type/size of engine
• advertised duration
• duration @ 0.050" lift
• installed w/any advance/retard?
• valve spring specs
• FT or roller
• solid or hydraulic
• "all in by" RPM
• how much timing does vac. adv. supply
• vacuum advance hooked to manifold or ported vacuum
Engine vacuum at idle
Carb type and size
Current carb specs:
• power valve
• accelerator pump cam
• squirter size
• turns on the idle mixture screws
• any changes that have been made from how the carb was originally set up
Along w/the vehicle specifics like:
• gear ratio
• trans type/ratio
The way you use the vehicle:
• w/e toy
• the symptoms of what is (or is not) happening
• what RPM the problem occurs
• what you're looking for overall
• anything else pertaining to the problem that may help diagnose it
 Systematic approach
Identifying problems or failures in any vehicle, regardless of the system that has a problem, can be approached in the same way. It is important to use the same basic rules and techniques to arrive at an accurate diagnosis and a successful repair. It doesn't matter if it is an unusual noise, a leak, or a "running" problem, if you stick to the same technique you will be successful in coming to the correct conclusion. This method can vary from person to person, but to be the most successful, it is important to stick to the same rules. In most cases, "knowledge is key". Everyone is familiar with this statement and in vehicle repairs it is absolutely necessary to to be well educated before you can begin to find the correct answer to a problem. It doesn't matter how much you know, everyone, even a well seasoned service tech, will find themselves in a position where they need more knowledge about a system before they can accurately diagnose the problem and perform a reliable repair. The most effective approach can be broken down to the following same basic steps:
1. Verify the complaint.
2. Correctly identify the effected system.
3. locate the failed component.
4. Replace the failed component.
5. Retest to prove the repair was successful.
Now these steps may look like common sense, but many are distracted as they proceed and end up "going down the wrong path" thus arriving at an incorrect conclusion and replacing the wrong part. If you are new to repair, I recommend that you write these steps down and stick to this approach on anything you desire to fix. Let's look at these steps one at a time.
- Verify the complaint. This is worded more at identifying what someone else is experiencing but does apply to complaints with your own vehicles as well. Start asking questions. Find out when the problem is most noticeable. If it is your vehicle pay close attention to the conditions under which you can easily recreate the symptom you have noticed. If it is someone else's vehicle be certain you have identified when and how the problem occurs so you are certain both of you are experiencing the same thing. Do not ever begin to remove or replace anything without doing this. Never act on an "assumption" or it will come back to bite you in the but. Once you have narrowed down how the failure manifests, you can proceed to the next step.
- Correctly identify the effected system. Here is where your research needs to begin. Using a detailed repair manual for reference during all repairs is recommended unless you are extremely familiar with the system you are working on. If you are new to repair, first research the possible causes. This can be done by using troubleshooting info from the manual, or by going online, or by finding someone who knows how to explain what the most likely problem could be. Even if you are a seasoned tech but don't know everything about the system you believe to be failing, detailed service manuals are important. Understanding how things are designed to work will help you to distinguish a failure from normal operating characteristics of this system. Many repair manuals leave out information about function and design. If you read a manufactures service manual you will find a description of what this system is designed to do. If you understand the "operating theory" of this system, you can correctly identify if it is working properly or not. This will help prevent you from replacing the wrong parts. Many people are embarrassed to admit that they don't know how things work, but regardless of how long you have been doing repairs, you will always come across things you have never seen before. It is critical to be honest with yourself and admit what you don't know. Here's where bulletin boards and the web come in handy. Ask as many questions as you can to learn everything you would like to know. There are also many publications with "basic automotive theory". Even though there are many new and innovative designs on the market today, the basic function of these systems are still the same as they were many years ago. Once you know how things are supposed to work you will be close to knowing what is wrong and approach the component that is the culprit and thus the next step.
- If this is a relatively new vehicle, be sure to look for any applicable TSBs (Technical Service Bulletins). Often these will outline the problem and supply a proven solution and can save hours of time and save a lot of money. In this case, Google really IS your friend...
- Locate the failed component. This one doesn't need much detail to explain. Now you are looking at the correct system, what's wrong with this systems performance, and identifying which component is most likely to be creating the failure. Now it is time to start the disassembly. Here is where you will begin to understand why steps 1 & 2 are so important. Many will begin taking things apart to explore what may have been the problem but exploratory surgery on a vehicle can be expensive and time consuming. Don't disassemble anything until you are reasonably certain that you are after the right component. If needed, take digital photos of the disassembly process and/or take written notes. This is especially useful if the repair will be interrupted for some reason. Important details will be forgotten if not noted.
- Replace the failed component. There are important issues here before you do this. First is buying the correct quality replacement part. It may be better to have the replacement part on hand before beginning to save time later- providing you're sure of what part is in need of replacement. At this point you have done your best to identify what part is needed. Having to stop, clean up, and put "stuff" away then head to the parts store can leave you working into the dark hours. Make sure by calling ahead that the component that's needed is actually available before you take anything apart. Some parts can be hard to find. Some parts are only available from the dealer. Sometimes there will be old or worn parts that will be removed during the repair, now is a good time to replace them, too. Don't forget things like gaskets, sealers, fluids, belts, hoses, etc. that may need replaced. Use a parts store that you are familiar with if possible. It is better to pay a little more for a quality part than to save some money by buying an inferior part unless there are severe budget restraints. After the old part is pulled, compare it to the new one to be certain the replacement part is correct. During reassembly, keep your notes, photos and manual handy. Here is where having taken photos and notes will really pay off. The manual will be able to give a warning of any special considerations that could crop up during the reassembly/parts replacement.
- Once you have the reassembly process completed its time to retest to verify the repair was successful. This can be a test drive in some cases. In other cases the repair can be verified by looking at a read out from a scanner before a test drive. When possible, duplicate the exact same conditions under which you were able to identify the original symptoms. If you followed this method correctly you should be successful.
 In conclusion
The most successful service technicians have all developed a technique similar to this one. Do not be discouraged if at first you find this difficult to do as this can be complicated, depending on the problem the vehicle is having. If you feel like you have "gotten in over your head", stop and research the situation. Someone, somewhere, has seen the same problem you are trying to identify and will know what you need to do. "Stick to the program", and as time goes on you will begin to do this automatically. It's a good idea to document your repairs and findings so they will be available for reference. Over time these experiences will add up and combine into a body of knowledge that will hold you in good stead for years to come.
Also many vehicle designs have "pattern failures", meaning the same thing goes wrong with many or all of each design. Just continue to verify the complaint, find the right system, replace the right part, retest and you will be successful. Have fun and good luck.
Bat Auto Technical site/forum, info on late model vehicles.