Rough start when cold?

Discussion in '6.9L IH & 7.3L IDI Diesels' started by SLittle, Nov 9, 2018.

  1. SLittle

    SLittle Registered User

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    Owned my '91 NA 7.3 idi now for only a couple months. No diesel experience at all.

    Yesterday after work I went to start the truck. It was about 25 degrees F outside and truck had sat for a couple days.

    One pump to set idle, wait to start light goes out, I crank it over. I probably cranked for 5-7 seconds. During that time it.. coughed? 3 times before it finally came to life.

    PO installed:

    Facet lift pump.
    New glow plugs (his words.. "the ones recommended on that oil site")
    New GP controller (his words.. "recommended one was expensive so I got a cheaper one")
    Lot of wiring repair regarding the glow plugs.

    Now, it started and runs fine, but it seems to me it should start easier than this even at 25 degrees. When it was warmer, it would "cough" once before coming to life.

    Is this normal? If not, what could be causing this?
     
  2. riphip

    riphip Supporting Member Supporting Member

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    Is normal.
    The colder it is outside, the longer it takes on GP cycles (as in more). Use some fuel additive that removes moisture and has lubricity for pump if you are not doing this already. Plug the block heater in the night before. Should start easily after this.
     
  3. robw

    robw Registered User

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    Not normal, these rigs should start down to 0* or lower with good batteries, glow plugs, ability to burn the plugs and tight fuel system.

    Your glow plug relay may not work well, you could try adding a momentary switch to the glow plug relay - looking at the engine from the front (straddling it as you have to on these guys), the bolts look like a diamond pattern - the top right 8mm bolt will switch the relay on if 12v+ is applied to it.

    Wire your switch to the battery, and that top right 8mm bolt, then when you press the button in the cab it will fire the plugs until they heat up and will shut off themselves. Your cab light and everything will say the same.

    Edit: If the batteries are sub-par, or the starter is going out, it won't crank hard enough to build compression and heat to fire, either. Your leads are also paramount to providing current from the batteries to the starter, you can make your own leads using 2/0 welding wire and cold weld crimp the connections (don't solder, the vibration will lead to it cracking). I use a hammer crimp and a 20 ton shop press to achieve this. If you make leads, do yourself a favor and switch to military style lugs and use 3/8 eyelet connections - you will thank yourself later.
     
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  4. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    That’s not out of range for normal, but it could definitely be improved. To me it sounds like more of a lack cranking amperage issue. If the glow plug system wasn’t perfect it wouldn’t have started at that temp.
     
  5. SLittle

    SLittle Registered User

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    Batteries - two brand new batteries. I can get the specifics off of them if necessary.
    Starter - brand new.
    Wiring - all 2/0 welding cable with military style lugs.

    This morning I decided to drive it to work. It was around 10* f. Truck hadn't moved for 4 days.

    One pump, turn key on, wait to start light goes out.

    Took about 10 - 12 seconds of cranking to come to life. During that time it coughed several times. Upon coming to life there was a cloud of white exhaust smoke.

    I'm really OK with this. I don't plan on using the truck in the winter and it does indeed start, but if something isn't right I'd rather fix it.




    I went inside and let the truck idle for 20 minutes. When I came back out I noticed a damp spot on the driveway. I have an ever so slight drip from the fuel heater. I'll have to pull this and replace the o-rings.

    **With the electric lift pump would this allow air intrusion and cause a hard start?**
     
  6. SLittle

    SLittle Registered User

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    I'm not quite following here... [background in electrical controls].. "Your glow plug relay may not work well" so manually activating it will make it work well? You mention wiring a manual switch in the cab to activate the glow plug relay. Are you referring to a momentary switch that will start the glow plug sequence or is this something I would hold in the on position until the glow plugs are warm? Doesn't the truck do this itself when the key is turned on?
     
  7. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    Yes you need to hold the switch until the glow plugs are warmed up enough to start. For the second one, yes it is supposed to, but if the relay isn't working right, it may not be keeping the glow plugs on long enough. Then they won't be hot enough to start the engine.
     
  8. MtnHaul

    MtnHaul Supporting Member Supporting Member

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    My guess would be that your GP wiring is producing excess resistance somewhere and the controller thinks the GPs are hot when they are not quite ready. The controller does not sense temperature but measures resistance, wich changes as the plugs heat up. A manual GP switch is much more reliable than the factory controller, although it is also easier to burn out the GPs since you control the cycle and not the controller. Personally I like the manual setup because you can still use the GPs even if several are not functioning. With the factory controller and several failed GPs the controller will likely just cycle/click on and off without ever really heating the plugs and your starter will then take extra abuse as it works harder to start the engine.

    Like you I have new batts, cables, starter and with a 10 second GP cycle my truck usually fires with just a bump of the key, and then the rest of the day I pretty much never need the plugs.

    There is a good article in the Tech section here that details the manual GP switch setup.
     
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  9. rewbrooks50

    rewbrooks50 Supporting Member Supporting Member

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    Northeast Texas, 30 degrees, I have the same slow starting. If I recycle the glow plugs wait to start , it will start normally.

    Warm temperatures it starts in 5 seconds or less.
     
  10. riphip

    riphip Supporting Member Supporting Member

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    Repair that leak & you should be good to go. If fuel can leak out, air will leak in when not under pressure of lift pump.
     
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  11. robw

    robw Registered User

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    Your relay could be bad, you could have bad wiring - I would attach a momentary to the switch and try that.

    Hard start and smoke when cold = low compression from lack of heat causing poor fuel combustion.

    15 seconds of cranking does the same thing the GPs do - heats the combustion chamber to start the combustion process.

    If you plugin a momentary and that doesn't fix it, I would bypass the relay with a starting relay and make it purely run on your momentary switch.

    12v starting relay == only burn the plugs 7-8 seconds at a time.

    The bonus of a momentary connected to the stock relay is the stock relay will cycle off when it suspects the cylinder walls are warm.

    If the gps are doing their job, your truck if everything is good (and your 2/0 wire with military lugs is the exact setup I went with, which is super skookum) will fire straight away.

    Good luck!
     
  12. robw

    robw Registered User

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    I didn't realize there was a low pressure leak, as stated if fuel can get out then air can get in... that will F your startability as soon as the fuel system depressurizes with air.
     
  13. austin92

    austin92 Full Access Member

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    I’m stumped on my truck too man. Only thing I’ve changed since last winter is R&D IP and injectors (8.5* timing) and it’s taking 15 seconds of cranking to fire. No return line leaks. Last summer I installed a new gp relay, motorcraft plugs, powermaster starter, and pair of new Napa legend group 65s. Compression was over 400psi. Battery cables look decent, it’s cranking plenty fast. Been taking over 10 seconds of cranking since it dropped below freezing so I verified 8-10 seconds of 12v to all 8 plugs and 5.3-5.6ohms on each plug. Started great last winter down to 0*, idk, I’m lost


    Sent from my iPhone using Tapatalk
     
  14. MtnHaul

    MtnHaul Supporting Member Supporting Member

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    Do you get lots of white smoke while attempting to start it?
    Have you tried an electric fuel pump or a new mechanical? Any sign of fuel leaks before the pump and filter head?

    With so many new parts I would be scratching my head tooo_O
     
  15. Black dawg

    Black dawg Registered User

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    How long do the glow plugs/wait to start light stay on? If you listen, you might hear that the wts light goes off before the glow plug relay actually shuts off. Should start quickly and cleanly at 25 deg.
     

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