LB7: crank no start lb7 headache

[blackthumb88]

its an 04 duramax. to start, heres a list of what all has been replaced...
-fuel filter housing
-cp3
-suction side fuel lines
-injectors
-injector supply tubes
-FRP sensor

currently getting 2 mpa at crank (fluctuated between 1 and 2). can hand prime at housing up to 10 psi (using test port beside alternator). have pumped until hard and bled at that test fitting as well until no air came out. when pumped up to 10 psi, slowly bleeds down to zero over the course of about 2 minutes. when cranking, ticks down to zero in about 15 seconds. no codes when scanned either

any ideas on where to look for an issue here?

 

[JRein]

Check all your fuses and relays?

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[DAVe3283]

Have you had to bleed a common rail fuel system before? It takes a lot of cranking. 4+ full 15-second crank cycles is not unusual from what I have seen.

What caused you to replace all those parts? What injectors & CP3 went in? New (and from who), or used (and from where)?

The lack of pressure at crank and bleed down on the supply side sound like a weak CP3. Have you done a return rate test on the CP3?

 

[blackthumb88]

Bled all air out at the test port and then went back and forth pumping and cranking about 8 times. No change in rail pressure while doing so. All fuses and relays seem to be normal, all injectors are receiving their 4 ml command while cranking. These parts were all replaced due to an injector hack job by another shop about a month ago. Tested the return rate of whole system, got 100cc. CP3 return rate by itself is 68cc. Got that spec from another shop, only return spec I could find was for the injectors saying a max of 4cc per injector, or 16 per head

 

[blackthumb88]

The main thing that has me worried here is the parts the owner got for this (i.e. the injectors and cp3) were borg warner remans from oreillys. had issues with them before on 6.0 and 6.4 powerchokes but not sure how they are in duramaxes

 

[DAVe3283]

The values I am finding for a return rate test is the following:

• 15 seconds of cranking at 150 RPM
  (ECU limits you to 15 seconds, so this is easy)
• Total fuel return from all injectors (excluding CP3) must be less than 2 oz (60 ml), though I have also heard 40 ml total max as well
• Total fuel return from CP3 should be less than 35 ml, though also heard 60ml.

It sounds like your CP3 return rate is out of spec, and your injectors are borderline, assuming those values were from 15 seconds of cranking. I would be looking at another CP3 to start with. And I wouldn't get it from O'Reilly.

 

[blackthumb88]

Do you happen to know of any way to test the cp3 itself? I definitely have a high fuel return value at the cp3 but I haven't been successful in trying to find a way to test the fuel pressure regulator on the cp3. not sure if the FPR defaults to straight return if faulty or not.

 

[briencolgan]

I am having similar issues with my 03 LB7. I am new here and hope I am posting this is in the correct location. I saw correct pressure at the fuel inspection port (8-10 psi) one day then nothing. I changed seals in the fuel manager and pumped and pumped. Nothing. then ran a hose from the fuel manager direct to a can of diesel. So the fuel manager is not the issue. I'm starting to focus on the metal fuel supply line that runs from the drivers side firewall to FICM. I tested that with a mighty-vac and it looks like there may be a small leak. But it's hard to hear anything definative. Also put that same line under 10psi positive pressure from compressor.

But my question is can I just bypass that steel line totally? I want to rotate the banjo bolt on the FICM inlet 180 degrees and bring a rubber fuel line across the firewall and connect in directly and just leave that pipe where it is. It looks like its a direct line from the tank with no junctions straight to the FICM.

 

[Awenta]

You can skip the ficm and go straight to the cp3 but you can't skip the filter housing. You would have no filtration and no way to prime the system.


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[briencolgan]

Great Thanks for that quick reply. If I go to FICM inlet then it looks like it goes out the ficm and then to filter housing then to low side cp3 so I'm good right?

 

[Awenta]

Great Thanks for that quick reply. If I go to FICM inlet then it looks like it goes out the ficm and then to filter housing then to low side cp3 so I'm good right?

Yes. And it tees off to that valve by the alternator.

If you wanted to eliminate things go from the tank to the filter to the cp3.


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[briencolgan]

Yes. And it tees off to that valve by the alternator.

If you wanted to eliminate things go from the tank to the filter to the cp3.


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I am talking about bypassing the pipe numbered 38. It looks like it goes direct to the ficm inlet. No T. But I don't see that valve in this drawing for some reason.

The only T I see here is after the fuel filter.

Where is that fuel inspection port you mentioned? Before ficm?
After filter?

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[Awenta]

That port comes off number 9.

I doubt the hard line is your issue


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[briencolgan]

Thanks for the clarification. I'm going to run that bypass and see I guess. I saw 5000psi at idle so I don't think a high pressure failure is likely. Do you have any ideas?

Why would the filter prime when I bypass that ficm and not prime when it is hooked up proper? I just ran a hose from the inlet to a can of fuel and it had good prime. But when I hooked it back to ficm. Nothing. And new lines are installed both supply and return from the valley lines to the tank.


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[briencolgan]

Here's what else I have done:
Ran crank no start tests on 6-2792 of the factory service manual.
2. Saw no codes
3. Observed no fuel leaks
4. Fuel rail pressure was within specification 159-203psi
5. Did my best to track down ignition one single parameter. Pretty sure observe battery voltage there.

6. Engine RPMs were good on starting and cranky.


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[Stancedlb7]

You can bypass the ficm. You can prime all day and create pressure but as soon as you crank pressure will drop without a lift pump. If your CP3 is creating good rail Id have it scanned as the ecm might be, cutting fuel, the cause. Try disconnecting your glow plugs and give it a tiny spray of starter fluid, will it run after? Becareful not to spray too much as you will over rev the shit out of it and cause damage.

 

[briencolgan]

7. I don't have a scan tool to check CKP parameters but was able to hook up a multi meter and see about 23 ohms on the harness?

9. I primed the pump by hand to eight psi's and it loses pressure in about two minutes. That No answer send you to step 31 which is replace the fuel filter housing. I didn't replace it. I just replace the seals.

11. Skipped the engine compression test for now. Because it was running like a top and just quit like it ran out of gas.

13. Fuel rail pressure when it was cranking was about 200 PSI's 229 to be exact.

That's about as far as I've gotten. My next step is to run through fuel pressure diagnosis high side. I've got the stinking feeling that this is something simple and I am way overthinking it.

8. Skip number eight it seems like a longshot.


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[Stancedlb7]

200psi while cranking!?

 

[briencolgan]

200psi while cranking!?

Yes. 300 now.


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[briencolgan]

Yes. 300 now.


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Ok. I'll try the ether. Thanks for the tip. Isn't rail pressure supposed to be higher when cranking?

This whole think stared with the truck quitting on a hill. It acted just like it ran out of gas. When I tried to start it again it made a sound I'd never heard up in the front middle of the engine. It sounded like a high pitched stripped gear. Never made it again.



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