No Start 1: Checking For Spark
It's been my experience that the majority of the cranks but does not start conditions I've troubleshooted and repaired (on GM 3.8L equipped vehicles) had their root cause in the ignition system.
So, my recommendation to you is to check for spark at all of the spark plug wires with a spark tester. Now, when I test for spark, I also test for fuel pressure with a fuel pressure gauge. It's not that I'm trying to see if I'm missing both fuel and spark (as mentioned before, usually one of them will be missing from the mix), it's just my way of speeding up the troubleshooting process.
Testing the ignition system on your GM 3.8L equipped vehicle isn't hard or difficult. I've written a tutorial that'll show you in a step-by-step manner and you can find it here: GM 3.8L Ignition Control Module and Crank (3X, 18X) Sensor Test (at: easyautodiagnostics.com).
Remember, the idea behind checking for spark is to see if all of the 6 engine cylinders are getting spark. Here are the most common causes of a no-spark result:
CASE 1: Spark was present in all of the cylinders. This result tells you three very important things: 1.) the crank sensor is good, 2.) the ignition control module is OK, and 3.) the ignition coil coil packs are good. You don't have to spend any time testing them or any money replacing them.
Your next step is to verify fuel pressure. Go to: No Start 2: Checking Fuel.
CASE 2: Spark was NOT present in all of the cylinders. This usually tells you that the ignition control module (ICM) or the crank sensor is bad. It's usually one or the other, I have never seen both go out at the same time.
Now, with no spark in any of the engine cylinders, this what I would suggest:
- Test the ignition control module using the following tutorial I've written:
- GM 3.8L Ignition Control Module and Crank (3X, 18X) Sensor Test (at: easyautodiagnostics.com).
- Test the crankshaft position sensor with the following tutorial:
No Start 2: Checking For Fuel
lack of fuel reaching the injectors is the other major and common cause of a no-start condition. The most common cause of this lack of fuel is an inoperative fuel pump.
The absolute best way to test the fuel pump is with a fuel pressure gauge. If you don't have one, you can buy one online or rent one at your local auto parts store (like AutoZone or O'Reilly Auto Parts).
If you need a more detail explanation on how to check the fuel pump, take a look at the following tutorial:
When testing the fuel pump (with a fuel pressure gauge), you'll usually see one of two results:
CASE 1: Fuel pressure is at specification. Not only does this result tell you that the fuel pump is OK but that the following components, that supply the fuel pump with power, are OK too:
- Fuel pump fuse.
- Fuel pump relay.
And so, there's no need to spend time testing them or money replacing them.
CASE 2: Fuel pressure is not present. This usually means that the fuel pump has failed, but not always. I would recommend testing/checking the following before condemning the fuel pump:
- After verifying that no fuel pressure exists, check that the fuel pump is getting power by tapping into the power circuit that feeds the pump with 12 Volts with a multimeter.
- Once you're tapped in, have a helper crank the engine while you observe your multimeter in Volts DC mode. If voltage is present (12 Volts), then you have confirmed that the fuel pump fuse and fuel pump relay are working perfectly.
- Confirming power to the fuel pump (with a multimeter) also verifies that the fuel pump has failed and needs to be replaced.
- If no voltage is present, as your helper cranks the engine, then the cause of no fuel condition is due to either a bad fuse, fuel pump relay.
No Start 3: Checking Engine Mechanical Condition
The engine in your vehicle could be bad and the source of the ‘cranks but does not start condition’. The way to find out if the engine is the cause of the no-start is to do a compression test.
Here are some more specifics:
- When performing an engine compression test, what you're looking for is an average compression reading of NO LESS THAN 90 PSI across all or the majority of the engine cylinders.
- If you have one or just two readings that are under 90 PSI your GM 3.8L equipped vehicle will still start and run, albeit with a misfire condition.
- I've written a ‘how to do a compression test’ article/tutorial that you may find useful. You can find it here: How To Do An Engine Compression Test (GM 3.8L).
