Getting to the bottom of what is causing your GM 3.1L/3.4L car (or mini-van) to crank but not start is not that difficult. In this tutorial/article I'll share some of my knowledge and experience so that you can find the exact cause of your vehicle's no start condition.
Whether you diagnose and repair it yourself or you take it to your trusty mechanic shop... you'll be able to save time and money by avoiding the all too common mistake of replacing parts you may think are bad.
Here are the contents of this article at a quick glance:
- Important Tips and Suggestions.
- No Start Condition Basics.
- No Start 1: Checking for Spark.
- No Start 2: Checking for Fuel.
- No Start 3: Anti-Theft System Checks.
- No Start 4: Checking Engine Mechanical Condition.
- No Start Summary.
- Related Test Articles.
You can find this tutorial in Spanish here: Cómo Probar un Arranca Pero No Prende (GM 3.1L, 3.4L) (at: autotecnico-online.com).
Important Tips and Suggestions
It's important to know that a no crank and a no start condition are not the same thing. Here's a brief description:
In a no start condition your engine does turn over when you turn the ignition key to start.. but the engine doesn't start. In other words: your vehicle's starter motor is cranking the engine but the engine is not starting.
A no crank condition means that the engine is not cranking when you turn the key to crank the engine. This is usually due to a bad starter motor, bad ignition switch, bad neutral safety switch, or maybe the engine threw a rod and is locked up.
If your vehicle is suffering a no crank condition, there's a good chance that it could be due to a low battery issue (due to a bad alternator) or a bad starter motor. The following tutorials may be good starting points:
- How to Test the Starter Motor (GM 3.1L, 3.4L).
- How to Test a Does Not Crank Condition (Case Study) (at: easyautodiagnostics.com).
- How to Test the Alternator (GM 3.1L, 3.4L).
No Start Condition Basics
One of the most important pieces of info you need to know, about what makes the engine in your car start and run, is that it needs 3 specific things when it's cranking. These three things are:
When one of the above is missing, the engine in your car or mini-van cranks but does not start.
To explain this a little further in very simple terms: The engine (internal mechanical) is the one responsible for the ‘air’ part. The fuel system is the one responsible for supplying the fuel (which in our case is gasoline). The or the ignition system is the one tasked with creating and delivering spark.
Here are some more specifics/details:
1.) Ignition System
- The ignition system is the one responsible for creating and delivering spark. Without spark, the engine will crank but not start.
- The ignition system of the GM 3.1L, 3.4L equipped vehicles covered by this article use a distributor-less ignition system. More specifically, it uses a coil pack type ignition system.
- In my experience, the most common component failures, of the ignition system that cause a no start no spark condition are:
- BAD ignition control module (ICM).
- BAD ignition coil pack.
- BAD crankshaft position sensor.
- BAD camshaft position sensor.
- All of the above ignition system components can be tested in a methodical way to find out exactly what has failed (if indeed something has).
2.) Fuel System
- The electric fuel pump (located in the fuel tank) is the key component that supplies the fuel the fuel injectors need to inject gasoline into the cylinders.
- When the fuel pump fails, it will cause a no start condition.
- Thankfully, the fuel pump can be tested with a fuel pressure gauge to make sure it has really fried.
3.) Engine Mechanical System
- The engine pistons and cylinder head valves (and all the other related components like: timing belts, etc.) are the ones responsible for the induction of the fresh air the engine needs for the combustion process.
- Although rare, internal engine mechanical problems can and do cause no start conditions.
- Possible internal engine problems are:
- Blown head gasket.
- Blown engine.
4.) Anti-Theft System
- The vehicles covered by this tutorial have a passive theft deterrent system that is an integral part of the PCM or body control module (BCM). Depending on the year of your particular make/model, your vehicle may be equipped with:
- PASS-Key system. Can be identified by the use of a resistor pellet on the ignition switch key.
- Passlock system. This anti-theft system superceded the PASS-Key system and does not have the resistor pellet on the ignition switch key.
- When a malfunction occurs in one of the components that make up the anti-theft system (usually the lock cylinder), the PCM disables the fuel injectors after the engine has started, causing the engine to stall after about 3 seconds of run time.
- PASS-Key/Passlock system failures are a very, very common cause of no start conditions.
As you can see, quite a few things, when they fail, can cause a cranks but does not start condition. I don't mean to imply that several things can go bad all at once... since it's rare to see (or have) two different components go BAD from two separate systems at the same time.
The light at the end of the tunnel, is that there IS a diagnostic strategy that you can use to figure out exactly what's wrong with your particular no start problem. Let's find out more about it in the next subheading...