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Amedee, GMC Technician
Category: GM
Satisfied Customers: 26063
Experience:  ASE certified tech with advanced level specialist. Wisconsin certified emissions state inspector
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My '07 Hummer H3 suddenly won't start. It cranks, but will

Customer Question

Hi, my '07 Hummer H3 suddenly won't start. It cranks, but will not start fully. I've tried the Learn method and that hasn't worked either. I did notice last week that it was idling a bit rough when I came to stops or red lights...I cAn hear the fuel pump hum when I turn the ignition on...I'm at a loss here. We tried jumping it, that didn't work. Any suggestions?
Submitted: 7 months ago.
Category: GM
Expert:  Amedee replied 7 months ago.

Hello and welcome!

My name isCustomerand I can assist you with your question.

Expert:  Amedee replied 7 months ago.

I have a lot of suggestions and things to try.

However, I would recommend that you diagnose the problem by checking for spark and fuel. Would you like me to elaborate on this?

Expert:  Amedee replied 7 months ago.

Or is there a security light on or flashing on the cluster?

Customer: replied 7 months ago.
The security light is not flashing at comes on when I turn the ignition on but disappears within seconds
Customer: replied 7 months ago.
Please elaborate on checking for spark and fuel
Expert:  Amedee replied 7 months ago.

Ok, then the problem is not related to the security system.

Customer: replied 7 months ago.
Any other possible suggestions?
Expert:  Amedee replied 7 months ago.

You will have to pinpoint what the engine is missing.

1. Spark

2. Fuel

3. Compression

All three of these are tested when the engine is being cranked over. There are two way of checking for fuel. Fuel pressure and fuel trigger. Both are very important and must be present for the car to start. Fuel pressure is self explanatory. You just hook up the gage and see what the reading is. Injector pulse is check with a noid light. The injector gets unplugged and the noid light gets plugged in to the injector clip. With the engine cranking over, this light must blink. This is the signal to the injectors from the computer. You can have all the fuel pressure in the world, but it wont matter if the injector is not pulsing gas into the cylinder like it should! All three tests play a very important part in diagnosing a no start condition. Be extremely careful when doing these tests. A simpler test would be to see if it runs on starting fluid. If it does, then you know you have spark and compression and you simply have a fuel delivery problem.

Customer: replied 7 months ago.
This is where my problem lies. I'm going to need to have it towed to have it diagnosed as I don't have the tools to diagnose it myself... :/
Expert:  Amedee replied 7 months ago.

Sounds good.

I am glad I can help!

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Customer: replied 7 months ago.
Thank you
Expert:  Amedee replied 7 months ago.

Your welcome.

You should see the rating system towards the top of the page.

Have a great night!

Expert:  Amedee replied 7 months ago.

Hello! It'sCustomerfrom just answer.

I am just checking in to see if you need any further assistance?

Let me know!