Diagnosing no starts on cars really needs to be approached in a logical manner. If you don't follow a standard flow of diagnosis you might replace parts that aren't needed and waste a lot of time looking for the automobiles problem. Note: There are several different no start conditions.
This page is about the crank's, but will not start type. Defined this means the battery on the car is good and the engine cranks around fine but does not fire up and run. If you're having a no crank situation I have information on car batteries on my other website. If the battery is good and you still have a no crank I have a page about starter motors and solenoids on this site.
Lots of people e-mail me with a simple question of why won't my car start. Unfortunately without being there it is just about impossible to determine what the malfunction is.
Even though I have 30 years of experience diagnosing automotive problems in many cases I find it necessary to follow a no start diagnostic chart from an auto repair manual for that specific vehicle.
In some cases you can check the basics and with a little luck discover the problem. Below I will provide some basic tools and information on things to check when your car will not start. This is for people with some prior experience with repairing their own automobile. When in doubt tow your vehicle to a professional mechanic for diagnosis.
If the engine will not start there is no harm in checking a few things before purchasing a service manual or calling a tow truck. But if you find yourself spending a lot of time and not uncovering any answers do yourself a favor and consider buying an online repair manual.
The service manual can be your most important tool in this situation. Some of the best information in these reference materials are the diagnostic tree charts.
When you are following a no start troubleshooting chart it will force you to stay on a path that is logical. We all know that the shortest distance between two points is a straight line. No start ladder diagrams designed for the specific vehicle keeps you on track.
You need three basic things to make an engine start. You need the proper fuel supply to the cylinder, you need air to be mixed with that fuel and then a spark to ignite it at the right time. Therefore diagnosing no starts needs to begin with determining which one of these items is missing.
If I am not following a tree chart where I start depends on the model of the vehicle. Example: if I am working on a Chevrolet product they provide a quick check pressure tap on the fuel rail right before the injectors. I can attach my fuel pressure tester to the rail in less than a minute.
I can then cycle the key from off to on a few times or even crank the engine and see if there is any fuel pressure. If there is the proper amount of fuel pressure I can move on to checking the spark.
The method that you use to check spark will also be determined by the year make and model of the vehicle. Whenever possible I use my specifically designed Spark tester to check for proper ignition. This takes some guess work out by making sure it exists at the right strength.
Even though distributors are seldom found on today's engines many models still have spark plug wires that run to the spark plugs themselves. In this case they make an inductive Spark tester that you can slip on the wire without disconnecting anything.
It will pulse as current flows through the ignition wire. In all my years of diagnosing no starts I would say that it is most common to either find a fuel system malfunction or a spark problem. Although keep in mind that in rare cases it can become much more complicated than these two basic items.
Once you determine which systems the malfunction is in you can go down that path to diagnose why that part of the equation is not functioning properly. Example if there is no fuel at the injectors it is time to start diagnosing the fuel pump and circuit.
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