Will not turn on, it sparks but will not turn on?

ROBERTO1580

MEMBER
2005 CHEVROLET SILVERADO
190,000 MILES

My 2005 Chevy Silverado z71 5.3 L will not turn on, it sparks but will not turn on. We already replaced the crankshaft and camshaft sensors, cleaned out the spark plugs, replaced the gas pump, and replaced the ignition starter but still no luck. I took it to Auto Zone so they can put on the Snap On computer to see if they can find whats wrong with the truck but it says that everything is fine. A mechanic friend of mine advised me that it could be the Mass Air Flow Sensor or the Trottle Body. My phone # is 956-639-3622 I would really appreciate some help.

1 Reply

SQM

MECHANIC
6,383 POSTS

Hello,

An engine typically needs spark, fuel and compression to start.
Since you are getting spark and fuel, it could be a issue with low compression.

You need to check the engine compression using a compression test tool.

General rule on a compression is the minimum compression in any one cylinder should not be less than 70 percent of the highest cylinder.
You should not have any cylinder less than 100 PSI
Here are the basic steps:

Engine Compression Test
Charge the battery if the battery is not fully charged.
Disable the ignition system.
Disable the fuel injection system.
Remove all the spark plugs.
Turn the ignition to the ON position.
Depress the accelerator pedal to position the throttle plate wide open.
Then use the compression tool to check.

Here are few helpful articles on how to check compression and typical symptoms of having low compression:

https://www.2carpros.com/articles/how-to-test-engine-compression
https://www.2carpros.com/articles/the-reasons-for-low-compression
https://www.2carpros.com/articles/symptoms-of-low-compression

I have attached the step by step procedure for your reference.

Please let me know if you have any questions.

Thank you.

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