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  1. #1
    Forestgnome's Avatar
    Forestgnome is offline Stainless
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    Default OT: F250 diesel hard starting when warm.

    A friend of mine has a 1999 F250 that intermittantly has a hard time starting when warm. He says it takes a lot of cranking before it fires. It always starts easy when cold. He doesn't have any other driveability problems. He says it runs perfect otherwise. He says it'll pull a boat up the ramp at idle. The camshaft sensor's been replaced, he's checked his glowplugs and the voltage to them. He's had this problem for a while now, even after having been to the dealer a few times. I know there's a lot of expertise here, so I hope you can help. Any ideas?

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    VDF4Ever is offline Plastic
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    if that's the 6.0L powerstroke it will only fire when there is sufficient oil pressure... Possibly an oil pump problem (weak pressure relief spring) or its in need of an oil change. It would explain why it does it only when warm.

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    Forestgnome's Avatar
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    Quote Originally Posted by VDF4Ever View Post
    if that's the 6.0L powerstroke it will only fire when there is sufficient oil pressure... Possibly an oil pump problem (weak pressure relief spring) or its in need of an oil change. It would explain why it does it only when warm.
    That's something to consider. He says it's an early 7.3L.

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    Limy Sami is offline Diamond
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    Fuel solenoid on the pump?........ have been known to go funny,. well in the Uk anyway.

    One balance though, if it has an oil pressure sensor linked to starter I'd be looking there first.

  5. #5
    gbent's Avatar
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    How about just plain low compression. When cold, the glow plugs come on and heat the air enough to fire. When its hot, no glow plugs. Anything in the cranking circuit that is less than optimal will make the problem worse.

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    Gary E is offline Diamond
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    Quote Originally Posted by VDF4Ever View Post
    if that's the 6.0L powerstroke it will only fire when there is sufficient oil pressure... Possibly an oil pump problem (weak pressure relief spring) or its in need of an oil change. It would explain why it does it only when warm.
    How does that make any sense?... ZERO oil pressure or close to it while cranking, specially a cold engine... Then you expect the starter motor to turn the engine fast enough and long enough to make pressure? and THEN allow ignition or injection so it fires?

  7. #7
    WHHJR is offline Stainless
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    Like it or not you should simply check the PCM for error codes.... Just about every curious soul has a code reader.

    8

  8. #8
    X-Y-Z is offline Aluminum
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    The Powerstroke 7.3l will also not start until some oil pressure has built up from cranking.
    The warmer the engine, the lower the viscosity so it takes longer to build pressure at the low rpm of the starter cranking.
    Change the oil to 15w40 throw on a new oil filter and I bet it starts fine.

    Just my guess from past problems on mine.

  9. #9
    mobile_bob is offline Stainless
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    how early is "early" 7.3
    the earliest were all mechanical injection, and likely as previously stated
    it may be low on compression and needs a bit of glowplug heat.

    that is easy enough to check, simply energize the solenoid when the engine is hot for maybe 15 seconds and see if it will then startup.

    other issues relate to a week transfer pump, sometimes the fuel Xover valve can draw air with hot fuel, and a plethora of other odd and less likely possibles.

    go with checking the glow plug heat, even if it is warm or hot it should come on for a few seconds, rather than just coming on and then immediately off again (which generally equates to some burnt out glowplugs)

    bob g

  10. #10
    Willy is offline Aluminum
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    The high pressure oil reservoir is leaking down when the engine is hot, probably due to cracked o-rings on the injectors. The o-rings fail from heat and time and also sometimes from extended drain intervals which takes it's toll. Cold starts are aided by the fact that the cold oil does not leak past the failed o-rings.

    Give it a quick 1 sec. shot of starting fluid into the air intake before starting. If it starts you know that it was not receiving fuel. If the high pressure oil reservoir was not bled down it should start instantly...like it does when cold.

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    11 Bravo's Avatar
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    Quote Originally Posted by Willy View Post
    ...............probably due to cracked o-rings on the injectors.....................
    That would be my first guess also. I had a 2000 F450 service truck with a 7.3 and I had this problem. Started good when cold, had to crank a bit when hot. It was the actuation oil seals leaking on the injectors.

    It is exactly as X-Y-Z explained. Cold oil is effectively heavier viscosity and builds pressure quicker. The hot oil is thinner and doesn't build the high pressure needed to actuate the injectors as quickly.

  12. #12
    mobile_bob is offline Stainless
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    i am betting it is a pre powerstroke mechanical 7.3
    he mentions checking the glowplugs and power to them,

    the power strokes have that funky valve cover gskt with the wiring that goes through, they fail with some regularity, but

    it is a major pain to check glowplugs on the powerstrokes and easy to do on the early mechanical 7.3

    the mechanical 7.3 does not have the high pressure oil pump, it has a mechanical injection pump

    i bet the glowplugs are timing out too quick, perhaps a bad timer or sensor

    we need to know how old of a 7.3 it is before we can figure out how best to diagnose it.

    iirc prior to '95 were mechanical, '95 and up were the powerstrokes

    bob g

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    WHHJR is offline Stainless
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    Do NOT use Starting Fluid. If the glow plugs are working...They Won't....

  14. #14
    Willy is offline Aluminum
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    I don't much care for starting fluid either, that's why I stipulated a very brief 1 sec mist.
    The glow plug circuit should not be active on a hot engine.

    The truck is a 1999 model, I'm assuming, (I know, I know), that someone has not installed an older mechanical engine.

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    willbird is offline Banned
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    Does starting fluid hurt a diesel ?? Some of my brother in laws John Deere Diesel stuff has a factory installed system to apply ether ??

    Bill

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    kenh is offline Titanium
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    Since it is a 1999 it has the oil actuated injectors.
    If low compression it would be very hard to start when cold.
    I vote for the high pressure oil system too.

    Better than chancing starting fluid hold a gas soaked rag in front of intake while cranking.

    As an aside, the g-plugs are separate from the G-plug light.
    In cold weather they may stay on for a max. of two minutes.
    In hot weather/hot engine they probably do not turn on, light illuminates as a self check.

  17. #17
    Willy is offline Aluminum
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    Not if used appropriately.
    A factory installed system, or others like it, use a calibrated "safe" shot to assist cold starts.

    But in the hands of an inexperienced individual a big blast into a very cold stiff engine at say -30 can do an awful lot of damage.
    I've seen bent con-rods and cracked blocks because some fool thought he had a miracle engine elixir in his hand.
    Like anything it has to be used with discretion.

  18. #18
    X-Y-Z is offline Aluminum
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    Quote Originally Posted by willbird View Post
    Does starting fluid hurt a diesel ?? Some of my brother in laws John Deere Diesel stuff has a factory installed system to apply ether ??

    Bill
    Not all diesels have glow plugs, the older industrial and big truck diesels in particular, some of these came with 'cold starting' feature, which is basically a can of ether plumbed into the intake, so you could give it a shot to start...thats no problem if used in moderation.

    On a glow plug equipped engine you could easily cause a internal explosion, or at least a external rapidly accelerating fire twards your face!
    Glow plugs are just that...they glow red hot when they are on. If an intake valve is open at the time you spray in, and the glow plugs are on....Well, there ya go! Instant fire.

    If you HAVE to start a glow plug diesel with starting fluid, either disconnect the large power wire that feeds the glow plugs at the soliniod, or at least turn the key on and wait for the glow plugs to finish cycling (which could be several minutes)

    Excessive use of starting fluid in any engine can easily cause cracked pistons and even heads among other things.

    As stated, its a 99, so it should be a Powerstroke, and he said it starts fine cold, so I would rule out the glow plugs anyway, any diesel should start fine when warm without glow plugs.

  19. #19
    viper is offline Titanium
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    As above, using Ether with glow plugs is a no-no! That will induce a severe knock on startup. The event starts early enough to cause rod and piston crown damage. That being said, I would most certainly get a small bottle of diesel and put that in the intake on a warm start (NOT TOO MUCH!). Remember that diesel cannot throttle the incoming air.

    This will tell you real quick if you are getting fuel during start up. If it pops off quickly, you may have a bleeding injector that reduces loaded pressure on the high side. If this problem is immediate (restart in 2-3min), I would suspect ECM tuning.

    7.3Ls were known to have longer start times when warm. I had one. Always started, just took some effort but popped off fine when cold. ECM commands more pump timing when cold when gets the party started quickly... More timing (earlier injection event) causes more charge heating. This is audible by the "rattling" and loud sound you get from the engine when cold.

    Another thing you should try is overriding the glow plug controller to manually put more glow time in. Most hot diesels barely use the glows at all but those red hot schlongs do a great job of getting the cylinder lit quickly.

    Again, spray diesel in intake to test for fuel issue, manually control glow time to see if that helps, Check batteries to make sure you are turning over fast enough. 7.3L take A LOT!!!!! of power to turn over and if they don;t turn fast enough, they don't lite....

    On the glows, voltage is not as important as amperage. That will tell you if they are working right. You can also testing the main input to the glow controller. example, 100A/8cyl = 12.5A each. Just gets you in the ball park...

  20. #20
    Murph is offline Aluminum
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    Quote Originally Posted by Willy View Post
    Not if used appropriately.
    A factory installed system, or others like it, use a calibrated "safe" shot to assist cold starts.
    They were never factory installed on an engine with GPs. The owners manual for the 6.5 I used to have says if needed a shot or two of WD40 will work.



    Andy

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