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Hard cold start on 1999 6.5 chevy. p0251 code

Discussion in 'GM 6.5 Diesel Engines' started by john aquina, Jun 3, 2018.

  1. john aquina

    john aquina New Member

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    Jun 3, 2018
    new york
    Hi, need some help with this truck. When cold (80 degrees this morning) it cranks and cranks then starts and runs rough with black smoke. In a minute that clears up and it runs fine. If I shut it off, it starts right back up fine.
    We have two year old injectors, glow plugs are new and work. starter and batteries are new and it cranks nice. Put in and relocated new PCM. Test the fuel output at purge valve and that seemed fine. Tested fuel pressure and that was within spec's. Changed Fuel filter twice. Checked it cold this morning and there was fuel in fuel filter canister. Just got it started and towed a small backhoe 30 miles and back. It ran fine, maybe a little short on power.

    ANY IDEAS !!!
    thanks
     
  2. ak diesel driver

    ak diesel driver 6.5 driver

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    Feb 7, 2009
    alaska
    Put a clear fuel line on the IP return line and check for air bubbles while running
     
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  3. WarWagon

    WarWagon Well it hits on 7 of 8...

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    Nov 15, 2009
    AZ
    Any codes? This acts like air. Park nose down make a difference?

    How many miles on injectors and where did you get them? China is 30k miles, not China is 100k maybe.

    Hard start wo air can be retarded timing from chain streach.
     
  4. john aquina

    john aquina New Member

    14
    18
    Jun 3, 2018
    new york
  5. Husker6.5

    Husker6.5 135' diagonal 16:9HD, 25KW sound!

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    Feb 10, 2011
    Lincoln, NE
    Sounds to me like you have one (or more) injectors leaking down. Sure explains the hard starting followed by black smoke that clears up quickly. I know, they are new, but as a wise man on here says all the time, "New doesn't mean it's good."
     
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  6. WarWagon

    WarWagon Well it hits on 7 of 8...

    8,246
    2,685
    Nov 15, 2009
    AZ
    Sounds like you have an air leak before the lift pump (to tank) if you are getting constant bubbles.

    How much drama do you get starting? Is it hit, stall back on starter, hit, stall, light off? All while spinning on the starter without releasing the key? I have a video of that - sticking China injectors.
     
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  7. john aquina

    john aquina New Member

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    Jun 3, 2018
    new york
    It cranks at least twice as long without any sign of starting, then starts to show signs of the hit- stall. It finally starts with black smoke running very rough for a minute then it runs fine. yesterday we towed a backhoe with it up some steep hills. It was laboring. When we got back it had thrown a P0236 code along with the P0251
     
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  8. Husker6.5

    Husker6.5 135' diagonal 16:9HD, 25KW sound!

    1,704
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    Feb 10, 2011
    Lincoln, NE
    Cranking with no sign of firing, followed by a attempt to hit intermittently and then lighting off is a sign that the injector(s) have no fuel in them at first cranking, followed by intermittent firing as they start to get fuel and then all firing as they finally get fuel. The black smoke once it fires off and runs, then clears, is easy. It's running really rich because raw fuel is sitting in the pre-cup/in cylinder/atop the piston. This fuel will NOT ignite on it's own while cranking w/ or w/o glows on because of its vapor pressure and flash point. It WILL ignite once there is a flame front established in the pre-cup that enters the cylinder and will stop smoking black once the excess fuel is burned off. Sounds like one of two things, either air is entering the fuel system and making its way to the IP/injector line(s)/injector(s), or you have an injector(s) leaking down after sitting for extended periods.
     
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  9. Husker6.5

    Husker6.5 135' diagonal 16:9HD, 25KW sound!

    1,704
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    Feb 10, 2011
    Lincoln, NE
    And unburned fuel sitting in a cylinder is BAD news for the motor as it will wash down the cylinder walls causing the rings and bore to wear abnormally fast due to lack of oil and/or lead to dilution of the oil in the crankcase which will destroy your bottom end bearings lickity-split.
     
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  10. john aquina

    john aquina New Member

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    Jun 3, 2018
    new york
    How can I find where the air is getting in to the system? is there a test?
    I did park the truck facing downhill last night and this morning it fired right up! Mayb cranked for 3 seconds.
     
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  11. Husker6.5

    Husker6.5 135' diagonal 16:9HD, 25KW sound!

    1,704
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    Feb 10, 2011
    Lincoln, NE
    Just a partial list of places to start looking. The O-ring that seals the FFM. Fittings in/out the FFM. IP inlet fitting. Dead LP can cause the IP to suck fuel all the way from the tank, and air in at any spot that isn't sealing.
     
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  12. Will L.

    Will L. Well-Known Member

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    Back to the very 1st response you got. Clear line of the ip return. It will cost about $3 and will take about 3 minutes to do.
     
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  13. john aquina

    john aquina New Member

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    Jun 3, 2018
    new york
    we put that in but didn't see that many bubbles on start or when running
     
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  14. Will L.

    Will L. Well-Known Member

    7,546
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    Jan 25, 2013
    Boulder City Nv
    Watch video in this thread. This is an older truck with didferent IP, but you’ll see what to do.
    This much air the truck barely runs sometimes and wont run at all others.
    http://www.thetruckstop.us/forum/threads/air-in-fuel-line-video.47087/#post-553394

    If you install the clear line and get bubbles or get no bubbles, that tells what to next. It should have been done before replacing the 1st ip.

    Show video of what you got. The video in the thread is nightmare status.
    If you cant post on youtube, can you text the video to one of us?
     
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  15. WarWagon

    WarWagon Well it hits on 7 of 8...

    8,246
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    Nov 15, 2009
    AZ
    FYI: After 30 seconds of cranking its not going to fire. You will melt the starter after 30 sec and the glows are cold. You are priming the system with 30 sec crank and 2 min cool downs.

    Park nose up. Before cranking after primed and sitting all night pop the hood and check the clear IP return line you put in. Is it full of air? Can you watch it through the crack of the hood while cranking? Report back. We are looking for the system draining back to the tank from air leaks. If no air is seen it could be just injectors stuck open or leaking just putting air in the injector lines. If you get lots of air you have an air leak and it could be injectors as the source - not as likely as a massive air leak elsewhere. In theory: The delivery valves in the distributor of the IP should keep the air in the injector lines - but slow leaks...

    Air leaks in the fuel system may not leak fuel. But a dead giveaway is a fuel leak. Inspect the entire fuel system for any damp spots. Hose clamps. The FFM has a heater that can leak out the wires. o_O

    I would put a pressure guage on the water drain and put it on the windshield. During lack of power see what it's doing. 0 may be a vaccum. Possible tank lining failing and clogged in tank sock. (Screen). Kinked hose?

    If I was to guess I would pull the easy driver side injectors and have them tested at a local diesel shop. I think they are sticking open. No offense, but I can't tell if you are shrugging your sholders at the air you are seeing. The nose down "cure" screams air leak because the system can't syphon fuel back to the tank easy.

    BTW ignore codes with fuel problems. Foam from air, or vapor lock, messes up optic sensor readings.
     
    Last edited: Jun 4, 2018
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  16. john aquina

    john aquina New Member

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    Jun 3, 2018
    new york
    I will tell you of all the places I have inquired, you guys are the most help. I will try it all and let you know
     
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  17. Will L.

    Will L. Well-Known Member

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    Boulder City Nv
    Thats why most of us are still here- bunch of people focusing on helping others instead of keyboard fighting
     
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  18. john aquina

    john aquina New Member

    14
    18
    Jun 3, 2018
    new york
    When the truck is cranked or just begins to run there is no sign of fuel unless it's so clean it's fully transparent) in the clear tube. After a few seconds when it is running a couple small air bubbles pass through. We cracked all 8 injector lines prior to cranking after sitting nose uphill over night and they were all dry for about 30 seconds then seems to get wet around the same time right before the truck started. It's hard to believe all 8 injectors are leaking down. Yesterday it seemed (truck was parked fairly level if not slightly nose down after opening the fuel filter to check and see if there was fuel in the filter housing the truck started fairly quickly then stalled like it used what ever fuel was in the filter housing then re primed. Most likely we have to pressurize the fuel system to see about leaks (there are no visible wet spots) Is there a procedure to do this? There is no fuel smell that leaking fuel should give but we do have to inspect the bottom of the filter housing for a leak (the truck did sit for years prior to us owning it for the last 2 years, this problem just popped up about 2 months ago.

    Would tank lining or clogged filter sock show sings of driveabilty like starving for fuel? The truck didn't skip a beat for over an hour worth of driving yesterday except for lacking power. It was hard to tell if the turbo is spooling but there was vacuum at the wastegate (I did not put a gauge on it yet or see if I could push the lever down at idle), but the vacuum pump is about 4 months old. The one thing that doesn't seem to point to the turbo is that the truck did not smoke at all when accelerating

    I would agree with air leak being the root of the starting problem, just not sure how to pin point it. Is there a check valve in the lift pump or anywhere that could be leaking back?
     
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  19. ak diesel driver

    ak diesel driver 6.5 driver

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    Feb 7, 2009
    alaska
    There is a check valve of sorts built in to the LP. Actually used in part of the pumping process IIRC. There's also rubber lines on top of the fuel tank. Also in areas where rust is an issue the lines coming out of the fuel tank pick up are know to rust through. It should be a leak pre LP or you'd have a damp spot.
     
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