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Discussion Starter · #1 ·
It's a stock 2016 with 225k. So I'm driving home today after work and getting the kids from school. I'm in medium traffic and go to accelerate and the truck has absolutely no power to accelerate. I look at the dash nothing new showing up. Shortly after this approx 1 minute limp mode comes on for 10 seconds then the truck dies. Try to restart and nothing, I figured I lost my prime so I go prime the pump and nothing. Go to open the bleeder screw not realizing it's plastic and I break it. Not a big deal AutoZone has the brass version and I found the hot screwdriver trick to get the rest of the threads out. My question is what fuses and relays should I be looking at first? The truck is currently on the street full of tools. They are fairly secure but I need this truck to make money! Any help would be GREATLY APPRECIATED!
 

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First thing I would suggest is getting it towed home or to a shop, then pulling the regulator/fca to see if it’s full of metal. If so, it’s time to dove into the fuel system because of a cp4 failure
 

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Get the truck back to your house and to safety. See if there are any codes stored. Ensure the batteries are fully charged and the cables are clean and tight.
Download the electrical manual for your truck here https://www.gmupfitter.com/wp-conte...Builders_Manual_Service_Manual_2016_en_US.pdf Lots of good information in this.

Am I correct that your fuel filter pump is now hard after pumping? No air coming out of the bled screw? Does the engine crank over but not start? Is your check engine light on in the dash? If so, get the truck scanned for codes. An inexpensive reader tool that will read and clear various codes is a great tool especially when there is no other information. I keep one in each of my cars and truck all the time.
 

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Discussion Starter · #4 ·
I'll be looking into the cp4 issue after determining no simple electrical issues. Fingers crossed over here.

The truck is outside my apartment when I say "on the street" my garage is underground so I couldn't get it safe. I was on the freeway when this happened and had my kids in the car so I looked over the codes quickly and reset to see if it would get me started even in limp mode I was 3 miles from home. The only code that stuck around is p128e.

The prime pump was as stiff as it's supposed to be maybe a little harder. But definitely not empty. That's why I think it's an electrical issue. If the pump failed wouldn't the truck have sucked all the fuel out of the filter before dying?

I'm going to go check the fuses that control the fuel rails and try to figure out what else electrical could be the culprit. I'll get my multimeter and try to figure out if the FICM is bad then check the FCA if everything else checks out. Then I guess start replacing stuff until it's back up?

This couldn't have happened at a worse time financially so I'm just praying for a cheap fix. Thanks for your input and help!
 

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Your truck doesn’t have a ficm, it’s controlled by the ecm on your truck
 

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Your truck doesn’t have a ficm, it’s controlled by the ecm on your truck
That explains why I couldn't find it haha. I read some people have had this problem with aftermarket fuel filters. I currently have a wix filter on and it's past due to be changed so I'm trying that tomorrow. After that I'm calling the mechanic because I don't have the skills for that.
 

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That explains why I couldn't find it haha. I read some people have had this problem with aftermarket fuel filters. I currently have a wix filter on and it's past due to be changed so I'm trying that tomorrow. After that I'm calling the mechanic because I don't have the skills for that.
If the primer bulb is hard then it’s not lack of fuel because of the filter. It likely wouldn’t have a hard primer if it was the filter. It’s unusual to have an air leak between the filter head and injection pump
 

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Discussion Starter · #10 ·
If the primer bulb is hard then it’s not lack of fuel because of the filter. It likely wouldn’t have a hard primer if it was the filter. It’s unusual to have an air leak between the filter head and injection pump
When the bleeder broke I pumped it to see if air would come out and I did have bubbles come up. Now the bleeder is replaced and the pump is very soft. I'm trying to find a mobile mechanic here in San Diego that can check it out. But I'm starting to plan for the worst.
 

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I hope you replaced the o-ring under the bleeder screw. If it fell out and you didn't know it was there, it may still be missing. Did you do the fuse check you mentioned earlier? Easy to do with a test light and will take less than 15 minutes.

Mobile mechanic, if he has some experience with the Duramax, might be the best thing to do.
 

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Discussion Starter · #12 ·
I hope you replaced the o-ring under the bleeder screw. If it fell out and you didn't know it was there, it may still be missing. Did you do the fuse check you mentioned earlier? Easy to do with a test light and will take less than 15 minutes.

Mobile mechanic, if he has some experience with the Duramax, might be the best thing to do.
I did make sure to replace the o-ring the old one broke off with it still attached. I looked at the fuses that were labeled "fuel anything" but beyond that I'm pretty useless knowledge wise. I didn't find anything blown under the hood and I didn't see anything that would controI engine stuff in the cab. I also rotated the two fuel relays to see if that would do anything. I'm replacing the filter tonight then priming for probably 25 minutes if it's anything like when I ran out of fuel. I have a multimeter if you could give me a heads up on where to check I would greatly appreciate it.
 

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Discussion Starter · #13 ·
Update changed the fuel filter. The old one was finger tight. Still no start I opened the bleeder to clear the air out. The prime gets soft after attempting to start so I don't know what that means.
 

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So once you crank the motor the filter primer will be soft.

I go with the recommendation that the mprop metering valve should be removed and check for any metal debris. If anything is found, well the infamous CP4 saga has come for your truck.

Stretching out the factory filter changes is not a good idea (unless running a lift pump system with additional filters).
 

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Discussion Starter · #15 ·
So once you crank the motor the filter primer will be soft.

I go with the recommendation that the mprop metering valve should be removed and check for any metal debris. If anything is found, well the infamous CP4 saga has come for your truck.

Stretching out the factory filter changes is not a good idea (unless running a lift pump system with additional filters).
It became due last week so I was planning on replacing this week when I had some time. The threads I have looked at make checking the valve look like a pain in the neck. Is there a simple way to remove it without taking all of my coolant lines off? I'm in a parking lot owned by the city and I don't feel like getting a ticket for spillage haha.
 

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Pump it, crank it, pump it, crank it, pump it, crank it. Being an LML might have to pinch the return line to give it some back pressure to start. I’m still thinking it’s a failure and you don’t really know until you find the metal in the system
 
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Discussion Starter · #17 ·
So after getting denied or ridiculous quotes to pull that regulator out I went and did it myself. Took a little more than an hour. You guys were right about the cp4. All bad lol looks like I'm converting to cp3 and a lift pump.
Medical equipment Wrist Gas Electric blue Service
 

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If the CP4 grenaded, you will need to replace the complete fuel system including:
HP Fuel Pump (CP3 conversion)
New Bosch OEM LML Injectors (x8)
OEM Fuel Rails
Injector return fuel lines
New Fuel Filter Head Assembly
New Fuel Tank (or update to oversize S&B)
Add a Lift Pump (Kennedy, AirDog II or Fass)
 

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Rob is right, more than just a conversion… although if it is done THOROUGHLY, the tank can be cleaned and probably a new sending unit to replace the pickup and level sensor
 
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