The two most common causes of a no-start condition, in my experience, are a lack of fuel or a lack of spark. This article will shed some light on the most basic steps that you have to take in diagnosing a CRANKS, BUT DOES NOT START condition.
To be able to take advantage of the info in this article, there are two important things to know. One is, the difference between does not crank and does not start conditions. Here's the difference:
- Does not crank.
- The starter motor does not turn over the engine for it to start.
- Does not start.
- The starter motor does turn over the engine.
- The engine turns over but does not start.
This article concentrates on the no-start condition. If you'd like to find out more about the does not crank condition, I recommend this article: How To Test A Does Not Crank Condition -Case Study (GM 3.8L). This link will take you to a real life case study of a car with such a problem.
You can find this tutorial in Spanish here: Vehículo Arranca Pero No Prende -Las Pruebas Básicas (at: autotecnico-online.com).
What Is A No Start Diagnostic?
A diagnostic is a series of tests by which you eliminate as good or bad the component you think is causing the problem. So, if the component (being tested) tests good, you then go on to the next component in the system and test that one. This process continues until the bad part is found and then replaced. To put it simply: A diagnostic is just a process of elimination and knowing this will give you a big testing advantage.
Now, many folks don't have the time and/or inclination to learn how to test the problem on their vehicle and just want someone to give them a ‘guess’ (that's right on the money) as to what the solution is to their car's NO START. With a modern computerized fuel injected car or truck, this just isn't possible anymore. So, I'll add the following to dispel some common myths about what an automotive diagnostic is not:
- Connecting a scan tool and reading the codes is not a diagnostic.
- Telling a mechanic or a technician the symptoms and receiving some suggestions as to the cause in not a diagnostic.
- The surest way to throw money down the drain is to replace something based on the two above lines.
OK, keeping the above in mind, the following testing tips and guidelines (in this article) can be modified to fit your particular need. Each no-start condition that you'll deal with will have a different thing causing it. And you're not going to find all of the tips and tricks here. The good news is that the testing tips in this article will give you a great head start.
Remember what I stated at the beginning of the article about fuel and spark? Well, to start this process of elimination as it relates to a NO-START CONDITION, we need to first find out if it's caused by a lack of FUEL or SPARK. How do we do this? With some very specific tools.
What Tools Do I Need?
You don't have to spend an arm and a leg buying tools to diagnose your vehicle's no-start condition, but you do need some and they are not expensive. To check for FUEL and SPARK requires two very important tools:
- A spark tester. Not just any spark tester, an HEI spark tester will only do (they cost around 7 - 14 bucks).
- A fuel pressure gauge. Depending on the type of vehicle you're working on, you can buy your fuel pressure gauge from the auto parts store or you'll have to buy a professional one online or from a tool truck (like Matco, Cornwell, etc.).
There are other tools that you'll need to be able to diagnose the NO START problem on your car or truck. Here's a very basic list of basic tools:
- A scan tool. It's a very handy tool to have, but when your car or truck doesn't start, this tool won't be much help (in the majority of cases).
- Fuel injector Noid lights.
- A repair manual.
- A multimeter. Preferably one that can read Hertz frequency.
- A 12 Volt automotive test light.
Knowing this, lets turn the page and start with the first test: the spark test.
Do's And Don'ts When Testing For Spark
Whether your vehicle has a distributor, or a DIS coil pack type system or a Coil-on Plug (COP) system, I suggest that the very first thing you should do in your diagnostic (of the no-start condition) is checking for spark. I'm gonna' give some helpful and effective testing tips in the next couple of paragraphs.
When testing for spark, it's very important to use a spark tester. Not just any tester will do. I recommend the HEI Spark Tester (the HEI stands for High Energy Ignition). If you want to know more about this tool, you can take a look at this article: The HEI Spark Tester. This article is within this site and is about how this tool works.
Using anything else or any other method will give you a false test result that'll have you wasting time and money. Not only that, you could damage the ignition coil in the process. Here are some specific examples of what not to do:
- Pulling the spark plug wire off of the spark plug while the engine is cranking to check for spark.
- Using a regular spark plug, instead of a dedicated spark tester tool, to test for spark.
- Using a timing light's flashing ON and OFF to verify if spark is coursing thru' the spark plug wire.
What The Spark Test Diagnoses
The components of the ignition system that the spark test is testing are:
- The ignition coil.
- On distributor type vehicles:
- The distributor cap.
- The distributor rotor.
- The spark plug cable.
- On distributor-less vehicles:
- Just the ignition coil(s).
- On distributor type vehicles:
Photo 2 belongs to a distributor-less ignition system and photo 1 to a distributor type system. The HEI spark tester is attached to the end of either the ignition coil boot or the spark plug cable.
After connecting the spark tester. You'll need to have an assistant crank the engine. You should see and hear a continuous spark crossing the air gap between the center electrode and the outside casing of the tester. Here are a few things to keep in mind:
- On a distributor type system it's important to test all of the spark plug wires and the ignition cable that feeds the spark from the ignition coil do the distributor cap. Why? Here are the three main reasons why:
- To find out if some of the spark plug wires are not delivering spark.
- This would cause the engine to flood out with gasoline, thus causing a no-start.
- To find out if the distributor cap is receiving spark but isn't sending it out to the spark plugs.
- This could be caused by the cap itself or the rotor. This is a very common no-start cause.
- To find out if there's no-spark at all, anywhere. If so the most likely causes are:
- The fuse that feeds power to the coil(s) is blown.
- The relay that feeds it this power is bad.
- The ignition module is bad.
- The crankshaft position sensor is bad.
- To find out if some of the spark plug wires are not delivering spark.
- On a distributor-less system, testing two to three coils should suffice. Why?
- The odds that all of the coils are bad at the exact same time are astronomical! In my experience I have never seen it happen.
- But if you have no-spark at two or more coils. The most likely causes are:
- The fuse that feeds power to the coils is blown.
- The relay that feeds it this power is bad.
- The ignition module is bad.
- The crankshaft position sensor is bad.
When you test for spark, all you're doing is trying to get a starting point for all of your tests. Why? Because depending on whether you get spark or not, you'll need to follow this up with more specific tests.
So, if you spark at more than one point (remember you have to test several wire or coils) or better yet, spark at all cylinders. Then you can forget about the ignition system as the cause of the no-start condition.
By seeing spark at multiple points, you now know that the ignition coil(s), the distributor, the distributor cap and rotor, the spark plug wires, ignition module and crankshaft position sensor are good. All of these components comprise the entire ignition system and you have just eliminated them.
Alright, the next step is to check fuel pressure. This is a must whether you get spark or not. Why? Because it's crucial to make sure that the ignition system is the only system not doing its job. But this part belongs to the next page, so lets go there.