Duramax guys?

Discussion in '1982-Present GM Diesel' started by max 02, Jan 27, 2020.

  1. Truckman4life

    Truckman4life 3/4 Ton Status Premium Member

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    The one forum post I read said something about their truck having issues starting when hot but they were getting a code. It was the fuel lines down by the trans. I was thinking maybe that was your issue since you mentioned something about the issue starting after the trans had been out so maybe the lines got disturbed enough to get the inside to come apart. I can't remember specifics but I know my brother in law has fixed a few duramaxes with fuel line issues.
     
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  2. max 02

    max 02 N.E.D. Premium Member GMOTM Winner

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    For sure something to look at again.

    Im sure a lift pump would overcome any line problems it may have or defiantly find any leaks.

    I got no codes, and zero power loss a WOT.
    I’m thinking a injector with high return rate or weak CP3 or the fuel rail plug is leaking.
     
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  3. max 02

    max 02 N.E.D. Premium Member GMOTM Winner

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    Oh and I like the price on the lift pump you suggested! I’ll look into that more after some more testing.
     
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  4. Truckman4life

    Truckman4life 3/4 Ton Status Premium Member

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    That lift pump is basically the one they ran on the 24 valve Cummins like the one your daughter has.
     
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  5. max 02

    max 02 N.E.D. Premium Member GMOTM Winner

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    Cp3 Checked out good.
    Went home and performed a return rate test. This test was done by disconnecting the return line under the truck at the fuel cooler, and catching the returned fuel in a container with the fuse for the FICM pulled so the truck won’t start, crank for 15 seconds. Measure fuel in container. 100ml is allowable.

    Truck passed at 55ml

    C67B9B47-6BCD-45A3-B716-51671972B154.jpeg
     
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  6. Truckman4life

    Truckman4life 3/4 Ton Status Premium Member

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    Red diesel? You sinner!
     
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  7. max 02

    max 02 N.E.D. Premium Member GMOTM Winner

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    Lol! All legal for me!
     
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  8. max 02

    max 02 N.E.D. Premium Member GMOTM Winner

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    Swapped filter heads between my 02 and Colby’s 01
    Mine still starts like shit warm. Colby’s is fine!

    I’m thinking my injectors are the problem... sure wish I could pin point it for sure. I don’t want to replace them all on a guess. This truck is miled out and probably not worth dumping another 3000 into it. Shity cause it’s worth nothing if she don’t start. But it runs perfect. Parts aren’t worth F all either. To many miles.

    988D9738-910E-4571-A57F-CFE6169F5E7C.jpeg
     
  9. Truckman4life

    Truckman4life 3/4 Ton Status Premium Member

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    Dang that sucks!
     
  10. 76zimmer

    76zimmer Flyin Rat Premium Member GMOTM Winner

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    I know you did a balance test, but are you suspecting them not firing correctly or long enough??.Isn’t there someway to test the firing of the injectors?
     
  11. 6872xtc

    6872xtc make mine modified Premium Member GMOTM Winner

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    How did the CP3 test go? As in, what is done to determine if it's building pressure fast enough? Asking because I don't know exact techniques.

    Also, how many miles on the truck? These will go a long time from what I have seen. But that doesn't mean that the rest of the truck will make it if rust has anything to do with it.
     
  12. max 02

    max 02 N.E.D. Premium Member GMOTM Winner

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    Delivery of fuel is fine it’s, the return back to the tank that’s being a bitch. No way of testing that with electronics. All manual and with the injectors under the valve covers it’s a pain to test individual injectors. So i’m stuck with a random test on them all or one bank,that I don’t have the fittings to do that test so I’d have to take it to a shop and then I still don’t know what injector it is just what side.

    Cp3 was tested with a Snap on reader by my buddy that is a GM trained teck. I don’t know all the numbers about what it tells you but he said the cp3 was in good order.

    My truck has 518 thousand klms on it. It was rusty!
    I fixed a lot of it but it still needs more work and the interior is not great either. It’s fine for a farm truck but I would not say it’s in great shape.

    I’ll get it figured out... just frustrated at this point.
    A lift pump would take away a ton of guessing on anything that may be an easy fix. But they are 900.00 bucks. Yeah it should have one.Yeah I want one. But it ran fine for all these years without it and if it doesn’t help and it is the injectors then it’s a waste on a old truck.

    Still starts ok when it’s cold I just don’t shut it off till i’m back at home and its in its spot in the garage! :haha:
     
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  13. 76zimmer

    76zimmer Flyin Rat Premium Member GMOTM Winner

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    Thats frustrating Dean, its been a pretty dam good truck for you over the years, and fun to ride around in too!
     
  14. max 02

    max 02 N.E.D. Premium Member GMOTM Winner

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    Indeed Dave! :waytogo:

    It definitely doesn’t owe us anything and has been the best vehicle I have ever owned.

    I’m not done with it yet!
     
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  15. 76zimmer

    76zimmer Flyin Rat Premium Member GMOTM Winner

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    Your truck was a big factor in my buying the 06 with 247k (400km) on it. I know you've been happy w it, no major mechanical stuff other than injectors, and I wont be racking up 20k on it every year either. Its perfect for what I need to tow the Maiden.
     
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  16. max 02

    max 02 N.E.D. Premium Member GMOTM Winner

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    You will be fine. The lb7s are the injector eaters.
     
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  17. Russell

    Russell LLY Escalade Status Premium Member GMOTM Winner

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    I'm not sure how I missed this thread!

    Sounds like you're on the right track as far as troubleshooting goes. First check the vacuum that the CP3 is capable of drawing. It should be greater than 10 inHg when you crank the engine with a gauge plugging the supply hose. You should also test the vacuum signal on the filter while the engine is running. If it is less than 2 inHg then you have a fuel system leak. Normal is around 5 inHg at WOT. It shouldn't be more than 7-8 inHg under heavy load. Common restrictions include the sock filter in the tank and pinched / kinked soft fuel lines. Common leak points include cracked fuel lines (soft or hard) or fuel filter assembly.

    Next is to check the CP3's fuel pressure outlet. To test the CP3 you'll need a mechanical rail pressure gauge to verify the electric pressure sensor and a scan tool capable of both displaying the rail pressure and commanding the fuel rail pressure regulator. Crank with the engine warm and the FICM disconnected to ensure that the engine builds at least the 115 mPa required for the engine to start. The CP3 should be able to build 160 mPa of pressure with ease and actual rail pressure should match the commanded pressure fairly closely. If it doesn't, then you need to figure out where your fuel is going. Common reasons for the inability to build rail pressure include excessive injector return rates, stuck / inoperative fuel rail pressure regulator, improper fuel rail pressure sensor readings, leaky rail pressure relief valve or a worn CP3. With the engine only having this issue when warm I would be looking close at the rail pressure relief valve. The engine may not be able to build the full starting pressure at cranking speeds if the PRV starts passing when the engine is warm. Once the engine is started, the CP3 spins fast enough at idle to provide enough volume to overcome the leak. The final check is return rates - Which you've kind of done already in a round about way.

    As for your next steps, I'd get your buddy to come back with his scan tool and verify that the fuel rail pressure sensor is accurate as compared to a mechanical gauge and then observe the rail pressure while cranking when the engine is hot to make sure it is building sufficient pressure while cranking to start the engine. If it isn't, my first recommendation would be the PRV. If that doesn't fix it up, then the CP3 itself would be my next suspicion.
     
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  18. max 02

    max 02 N.E.D. Premium Member GMOTM Winner

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    Thanks Russel! I was going to call you but I didn’t want to hassle you again! Lol!

    To bad that PVR isn’t as easy to get at as a LLY or newer engine. I’d just shim it really quickly and try it.
    I replaced the supply line in front of the ABS module Friday, Didn’t help.
    I’m goint to try some clear hose off the fuel filter and look for air, before I cut up more of my factory hoses. If that doesn’t show anything I will see about getting some manual gauges. Or I could just take it to MPl in Lacombe. I talked to Ted about it and he mentioned nearly the same procedure you have described.
    I don’t really what to spend hundreds of dollars at his shop for testing. But it could be cheaper than me buying specific tools and still not knowing what I’m doing!? :thinking:

    At least Colby’s truck is all back together and running good! :haha:Kates Dodge is alway home too.

    Kris’s dad said just drive his 2012 and park ours in the row of death. That’s not really what I want to do.
     
  19. Russell

    Russell LLY Escalade Status Premium Member GMOTM Winner

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    Unfortunately I don't really have the right test equipment to loan you either... I've never had to mess with the HP side of the injection system. I used a carb vacuum gauge to test the CP3 suction once.

    I don't know that the tools to test are terribly expensive, but I am willing to bet a couple hours diagnostics costs would be similar.
     
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  20. max 02

    max 02 N.E.D. Premium Member GMOTM Winner

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    We have everything Snap on sells for changing Lb7 injectors and injector cups but that’s it. Investing in some more gauges and fittings might be worthwhile?
     

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