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Pete, Auto Service Technician
Category: Chevy
Satisfied Customers: 24143
Experience:  14 years GM dealer Technician.
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2004 chevy: duramax diesel loses prime and wont crank after sitting

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My 2004 chevy duramax diesel loses prime and won't crank after sitting. I have to pump the primer about five times to get it to crank.
Hi,welcome to Just Answer.I will be happy to assist you with this question today.I will try and assist you as best as possible from here,feel free to ask any follow up questions to my info provided here.

From what you have described here this sounds like you may have a leak in the fuel system.The injection pump pulls a vacuum from the fuel tank through the fuel filter.If there is a leak anywhere when cranking it over the pump will suck air making it hard to start and requiring to be hand pumped.This can be a common fault as I have seen and have had to correct before.

The best way to find this leak if pump the primer with the engine off about 10 to 15 times until it is firm,then inspect the fuel lines from the tank to the fuel filter and from the filter to the engine for any fuel seeping out,inspect around the filter as well.

Any leaks found need repaired.

With the engine running you usually wont see fuel leaking as the pump is sucking in the fuel and sucking past the leak but with it primed up or pressurized with the primer you can usually locate the leak easily
I just need a little more info to assist better.
If your fuel filter is restricted it will also cause this as well.This filter should be replaced about every 10,000 to 12,000 miles.

Hope this helps, and please remember to indicate that I have helped you today.
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