Symptoms of 2004 GMC Sierra 1500 No Start

This 2004 GMC Sierra 1500 No Start problem was reported after this ATS customer replaced his distributor assembly. He replaced it because it has no spark and after replacing both the ignition control module and ignition coil. The engine  actually started after replacing those parts but the engine ran a little bit rough. He double checked every ignition connections and wrings but later the engine would hardly start.

Once in a while, it would start and when the customer monitored the scanner for live data stream, he can observe the sensors, timing advance/retard and fuel trims and everything seemed OK. He also stated that the distributor was bought from the local parts store after he spent so much money on the module and coil.

Diagnosis of 2004 GMC Sierra 1500 No Start:

When diagnosing for any vehicle no start, you can begin the analysis by getting any codes stored in the vehicle engine’s computer memory. This way you have a head start whether the problem is electrical or mechanical. A code usually means an electrical problem like sensor, outputs like alternator, injectors and other solenoid components. If you can get the engine running, scanner live data stream is the best way to monitor the engine components like: how the oxygen sensor are working? are they fluctuating or lazy? Oxygen sensor usually determines how the engine is using fuel.

Another is the fuel trim, is it working normally? for specific engine, the range values of fuel trims (called LTFT or STFT) can be found in the scanner or you can check with ATS. How are the injector wave patterns? The same pattern can be displayed in “live data stream” of your scanner. This injector wave pattern can be seen and compared for each cylinder. The same can be said about the crank and cam sensor wave pattern which are also shown in your scanner.

Is the coolant sensor matching the actual engine temperature? Example: if the coolant sensor is stuck at lower temperature mode, the ecm will think that engine is still cold after warmed up and feeds more fuel. This is the same principle when using the old carburator where you have the rich setting during cold start ups (called “choke adjustment”).

Once the engine is hot, the carburator automatic setting change by opening the throttle plate which will give it more air and make the fuel mixture lean. A lot of times, the engine is flooded because the coolant sensor is stuck in cold mode after the engine has already warmed up.

Once you have verified in your scanner that all the electronics are normal, it is safe to assume that the problem is mechanical. You can verify that too by checking the cylinder compression readings. Any cylinder with compression pressures lower than 100 psi needs a look at the integrity of the engine.

Another factor to look at is the vacuum reading. Is it below than 17 inch of Hg? A cheap $10 vacuum gage is usually available in your local parts store so you can test the engine vacuum. Another use of the vacuum gage is to check if the exhaust muffler is plugged. ATS has all these vacuum specifications for you so you can check and verify if the exhaust system is plugged or not.

Final fix for 2004 GMC Sierra 1500 No Start:

The ATS customer was advised about these tips and the following day, he found the problem. The distributor he bought was no good. He returned it to the store after trying a 2nd one which did not work also. He bought a new distributor from a GM dealership and the problem was solved. He figured if the engine is good but start only if you crank it for a long time… it must be the aftermarket distributor that he bought.

To check, he removed the spark plugs and found them to be wet. He knew from the scanner that the coolant sensor reading was Ok but still the plugs were wet. Conclusion? Weak spark. He then remembers that he bought a cheap distributor to cut his costs after buying the expensive ignition module and coil which he did not need.

More tips for 2004 GMC Sierra 1500 No Start:

1.) The way to solve any troubleshooting problem is to have a step by step procedure. Trying to guess and replace parts without verifications is the costly way to fix a vehicle problem. ATS is always there for you to give you one on one assistance by email when you have a vehicle problem.

2.) Trying to cut corners and neglecting your basic troubleshooting checks is a sure way to failure.

Thanks,

Richard