How To Troubleshoot A No Start (GM 3.1L, 3.4L)

No Start 1: Checking For Spark

The majority of the cranks but does no-start conditions I've troubleshooted and repaired (on GM 3.1L, 3.4L equipped vehicles) had their root cause in the ignition system. So, the ignition system should be the first thing to check.

Testing the ignition system, to see if it's the cause of the no-start condition on your car or mini-van simply involves checking that all of the six cylinders are getting spark. This is accomplish by connecting a spark tester to the spark plug wire and then having a helper crank the engine while you see if the spark tester sparks or not.

This is what you're looking for:

1. Check that all 6 spark plug wires are sparking with a spark tester.
2. If spark is present at all 6 spark plug wires, then you can conclude that:
   • The spark plug wires are OK.
   • The crank sensor is good.
   • All 3 ignition coils are good.
   • The ignition control module is good.
3. If there IS NO spark present at all 6 spark plug wires, then the most likely cause would be that:
   • The crank sensor could be bad.
   • The ignition control module could be bad.

Testing the ignition control module and the crankshaft position sensor can be done by you and the following tutorials will show you how:

• Testing The Ignition Module And Crank Sensor (GM 3.1L, 3.4L) (at: easyautodiagnostics.com).

It's extremely rare to have all 3 ignition coils bad or all 6 spark plug wires bad but if you're interested in testing them, the following tutorial will help:

1. How To Test The Ignition Coil Packs (GM 3.1L, 3.4L) (at: easyautodiagnostics.com).

If you confirm that the there's spark available to all six cylinders, then the next step is to make sure that the fuel pump is working.

No Start 2: Checking For Fuel

As you probably already know, the fuel pump is the one that provides the fuel (gasoline) the engine needs to start and run.

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).

The basic fuel pump test (with a fuel pressure gauge) is like this:

1. If the fuel pressure test gauge indicates at least 35 PSI, then you can conclude that the no-start condition is not due to a bad fuel pump.
2. Seeing 35 PSI, on the fuel pressure gauge also tells you that:
   • The fuel pump relay is OK.
   • The fuel pump fuse is OK.
3. If the fuel pressure gauge registers 0 PSI, this usually tells you that the fuel pump has fried and needs to be replaced. I suggest that before replacing the fuel pump you check that:
   • 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.

The following tutorial will walk you thru' the fuel pump test in a step-by-step manner:

• How To Test The Fuel Pump No Start Tests (GM 3.1L, 3.4L).

If you confirm that the fuel pump is functioning correctly, then the next step is to eliminate the anti-theft system as the cause behind the no-start.

No Start 3: Anti-Theft System Checks

The most common failure of the anti-theft system is the PCM (or BCM) not recognizing the key that you're using to crank and start the engine.

When this happens, the PCM disables the fuel injectors after a few seconds of engine run time. In other words, the engine in your car or mini-van starts and runs for a few seconds and then shuts off.

Unfortunately a PASS-Key/Passlock failure mimics a failed fuel pump problem and usually makes the vehicle owner think that the fuel pump has failed.

Here are the basics of what you should do to find out if the PASS-Key/Passlock system is the one keeping your car or mini-van from starting:

1. Check fuel pressure with a fuel pressure test gauge because an anti-theft problem will not disable the fuel pump.
   • If fuel pressure is at specification, the next step is to check for spark.
   • If fuel pressure is NOT at specification, then the PASS-Key/Passlock system is not the cause of the no-start condition.
2. Confirm that there's spark in all 6 spark plug wires because the anti-theft system will not disable the ignition system.
   • If spark is present at all 6 cylinders, the next step is to see if the engine starts with starting fluid.
   • If spark is NOT present at all 6 cylinders, then the PASS-Key/Passlock system is not the cause of the no-start condition.
3. Start the engine with starting fluid.
   • If the engine starts (even though it'll stall after the starting fluid you sprayed into the throttle body gets consumed), then you have confirmed that the PASS-Key/Passlock system is keeping the engine's no-start condition.

The PASS-Key/Passlock systems leave specific trouble codes in the PCM or BCM's memory when a failure occurs in one of its components. Unfortunately, you need a professional level scan tool (the ones that cost US$ 2,000 +) to read these codes.

This doesn't mean you can't correctly pinpoint the PASS-Key/Passlock system as the culprit behind your vehicle's no-start condition.

No Start 4: Checking Engine Mechanical Condition

The engine in your vehicle could have ‘thrown a rod’ or have a blown head gasket and be 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 and a blown head gasket test.

Here are some more specifics:

1. 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.
2. If you have one or just two readings that are under 90 PSI your GM 3.1L, 3.4L equipped vehicle will still start and run, albeit with a misfire condition.
3. The following tutorials may be of help:
   • How To Test Engine Compression (GM 3.1L, 3.4L).
   • How To Do A Blown Head Gasket Test (GM 3.1L, 3.4L).

No Start Summary

Your GM 3.1L, 3.4L equipped car or mini-van is a complicated machine but, not impossible to diagnose/troubleshoot it when it doesn't want to start and run.

The key to saving yourself time and money, when troubleshooting a cranks but does not start condition, is to check the basics first. The basics are spark, fuel and air (engine cylinder compression).

To check the basics, you need tools. There's just no way around it. One of the analogies that I've always enjoyed repeating, about doing a job without the right tools is like trying to eat a bowl of soup with a fork.

So besides knowing what to test, you need tools to do those tests. You don't have to spend an arm and a leg, since you can buy a lot of diagnostics tools that are tailored for the pocket-books of the serious do-it-yourself-er. Here are some of the basic tools you'll need:

• Fuel pressure gauge.
• Spark tester.
• Compression gauge.
• Multimeter.

Related Test Articles

You can find a complete list of tutorials here: GM 3.1L, 3.4L Index Of Articles. Below, is a sample of articles you'll find in this index of articles:

• How To Test Engine Compression (GM 3.1L, 3.4L).
• How To Test The MAP sensor with a multimeter (GM 2.8L 3.1L, 3.4L).
• How To Test The Fuel Pump No Start Tests (GM 3.1L, 3.4L).
• How To Test The Ignition Coil Packs (GM 3.1L, 3.4L) (at: easyautodiagnostics.com).
• Testing The Ignition Module And Crank Sensor (GM 3.1L, 3.4L) (at: easyautodiagnostics.com).