LLY Cranks fast, wont start when Hot
 

This 05 GMC Duramax, driven 150,000 miles hard, use lots of offroad fuel, always changing the fuel filter, older Edge with Attitude, big intake, 4" Turbo back exhaust, new batteries.....

Starts best in the morning, not instantly, but within 3-4 seconds.

I drive 1.5 hrs to work, and it wont restart without starter fluid which I hate to use and avoid at all costs.

Seems to start easiest when cold. My suspicion is, hopefully, a bad flex line that may be collapsing.

Anyone have any experience with a problem like this??

I am not very familiar with diesel/duramax tech.

Thanks!!!!!

Check your fuel filter(s)? I had a loose one before up front and it cranked but no start. I have heard of fuel pump housings cracking to form air in the system on these LLY's. Do you have a lift pump? Your CP3 may be getting tired. It is for sure a fuel issue based on what you wrote.

Fresh, tight filter. I installed clear fuel line entering and exiting filter housing. The line exiting to the fuel control module doesn't stay "full" there is air that will not go away. Yet, the truck runs perfect. Drive perfect. Full power thru 3500 RPM. I will drive it to work today and see if this starting problem persists. I found someone who has a computer diagnosis program that may be able to check the fuel system components.

So i removed the plastic cap on the fuel line behind the alternator. I guess thats where I test rail pressure? We put a hose on it, filled it with fuel, and pushed the pin with a rod... it kept taking fuel. We added about 2 cups. Seems that portion of the fuel system is starved (immediately after the fuel module behind alternator). Kept turning engine over with a sprits of starter fluid, finally started, ran perfect. Having a hard time locating a shop with equipment to test/service this motor.

So some module or something is not functioning when truck is operating temp.

If I open the hood to cool it quicker, after running it, it starts right up after a couple minutes. If hood remains closed, it takes considerable time to want to start again.

Ive heard of people having their truck start fine when it's cold but when it's warm it doesn't want to start. It's most likely air getting into your fuel system (fuel rail, pump, filter housing) or a bad injector(s). Any air that you have in your fuel system will cause hard or no starts.

Sounds like you have got yourself a "hot start" problem. I'm sure you figured that out. I haven't had that before on a duramax... On '04-'07 powerstrokes that exact problem is caused by a bad fuel pressure sensor lying to the computer. Try and google LLY hot start problems.

you need to check with a scan tool what your rail press is while cranking, could be a weak fuel press relief valve, bad injector or two, something along those lines. deff. need to get a hold of a scan tool.

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That port is where you measure filter/system restriction. Its under vaccum. dmax doesnt use a lift pump in truck applications it relys on vaccum supplied by the cp3.

Yeee Haaa.... Almost 2 years of hardly using the truck, i kept researching, reading, and contemplating.... I ran balance Test with a Snap On scan tool. Injector 2 and 8 were off the charts... SO... I did a DIRECT INJECTOR FLUSH Cleaning and it seems to have corrected the problems of hard start / no start. I disconnected the fuel supply and return lines on the driver side at engine, connected 6ft of fuel line directly into a tank with 1.5 gallon Heating Oil, 1 gallon Amsoil Injector Cleaner, and a quart GM Delco upper engine cleaner... Shazammmm... Runs like new. I will check in if anything changes, or soon, if she's still starting properly.

Truck has 170,000 miles and the engine is all original aside from Edge Juice, EGR Delete, Big Intake, Big Exhaust.

CLEAN THE INJECTORS BEFORE YOU BUY NEW ONES.