Duramax troubleshooting

1gr8bldr said:

I'm sure it has a fuel pump. But it also has a primer button on top of the fuel filter housing. To bleed it, there is a nut to loose, someone turns the motor over until all the air is out and then after tightening, you pump the button until it gets hard.

Click to expand...

mwilliams80 said:

My question is does it spin over and not crank, or does it not spin over at all, you turn switch over and nothing or?

If it doesn't spin over at all, maybe something is up with your 4x4 and not allowing it. Need more info.

Click to expand...

JpEater said:

Do not turn the engine over untill all the air is bled out of the system.

Proper bleeding procedure for a Duramax Diesel of ALL year models.....

Step 1: Open plastic slotted bleeder screw on top of the filter housing a few turns.
Step 2: Prime the primer until you get a steady stream of clean diesel fuel with no air bubbles present.
Step 3: Lightly snug bleeder screw.
Step 4: Prime the primer a few times. After 2-3 pumps, you should notice it firm up.
Step 5: Crank up the truck.

Note: Plastic bleeder screws are very prone to cracking. The engine will NOT run if its cracked and sucking air. Merchant Automotive sells a machined Bleeder screw that will not break.

Click to expand...

JpEater said:

Always start with the basics....

First thing is Fuel. A Duramax will not run with any type of an air leak in the fuel system due to the fact that there is no electric fuel pump to pressurize the system. The fuel system is 100% mechanical with NO relays for a fuel pump. It works off of vaccum. It "pulls" fuel to the engine. 99% of all fuel problems are caused by either an improper fuel filter installation sucking air, a cracked or stripped out water in fuel sensor (bottom of fuel filter), a cracked bleeder screw, or leaking seals in the primer assembly. Start by checking for air in the system. You can loosen the bleeder screw and prime is a few times. If you have air bubbles present in the fuel stream, you have an air intrusion caused by one of the above mentioned places most likely. If you don't have air bubbles when priming, you likely have another issue.

One thing that you didn't state was how it shut off. Where you on the throttle when it died? Did it just shut right off or kinda sputter out. Feel free to PM me a number and I'll be more than happy to walk you through some things to check. Normally a Duramax won't just die unless its a fuel problem. There are other circumstances obviously, but they are pretty uncommon on a duramax.

You didn't state which model engine you have. Is it an early 04 (LB7) or a late 04 (LLY). You can determine that by looking at the 8th VIN digit and seeing if its a 1 or a 2.

Keep in mind, these are just the first of many steps involved in diagnosing it. There are many more...

Click to expand...

JpEater said:

Always start with the basics....

First thing is Fuel. A Duramax will not run with any type of an air leak in the fuel system due to the fact that there is no electric fuel pump to pressurize the system. The fuel system is 100% mechanical with NO relays for a fuel pump. It works off of vaccum. It "pulls" fuel to the engine. 99% of all fuel problems are caused by either an improper fuel filter installation sucking air, a cracked or stripped out water in fuel sensor (bottom of fuel filter), a cracked bleeder screw, or leaking seals in the primer assembly. Start by checking for air in the system. You can loosen the bleeder screw and prime is a few times. If you have air bubbles present in the fuel stream, you have an air intrusion caused by one of the above mentioned places most likely. If you don't have air bubbles when priming, you likely have another issue.

One thing that you didn't state was how it shut off. Where you on the throttle when it died? Did it just shut right off or kinda sputter out. Feel free to PM me a number and I'll be more than happy to walk you through some things to check. Normally a Duramax won't just die unless its a fuel problem. There are other circumstances obviously, but they are pretty uncommon on a duramax.

You didn't state which model engine you have. Is it an early 04 (LB7) or a late 04 (LLY). You can determine that by looking at the 8th VIN digit and seeing if its a 1 or a 2.

Keep in mind, these are just the first of many steps involved in diagnosing it. There are many more...

Click to expand...

bandit819 said:

If you had air in the lines it will happen again and more frequent. It did for me. I would get a new bleeder screw. bleeding and priming are a pain.

Click to expand...

1gr8bldr said:

I have the early model, whichever that is, LLY, I think. You must be right about "air intrusion", because the mechanic bleed the system and it fired right up. If I had suspected this, I would have done it in the field. You got me thinking, last year when they claimed they put a fuel pump relay on it, I wonder if this was all they done to it but wanted to justify a higher charge for their trouble. ???

Click to expand...