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Detroit Diesel 6-71ti starting issue

Discussion in 'Technical Discussion' started by Posterboy91, Jan 23, 2019.

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  1. Posterboy91

    Posterboy91 New Member

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    i have a 1984 J&T 6-71ti 450hp. It’s really slow starting but when it does it lets out a light gray smoke and there is a slick in the water. After engine warms up to 120+ no more smoke and the slick is only as start up. Thoughts?

    Admin Edit: Oversize images removed.
    Last edited by a moderator: Jan 23, 2019
  2. Pascal

    Pascal Senior Member

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    Sounds like a bad injector or a poorly tuned up rack. How does it run under load? Some smoke at start up is normal in in colder weather. Try paraleling the batteries to see if it cranks faster
  3. Capt Ralph

    Capt Ralph Senior Member

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    Is this a new symptom? Happens when it's cold? Cold 40w oil?
    Engine history & hours?

    Block heaters available?
  4. Posterboy91

    Posterboy91 New Member

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    boat has 1700 hours original. has 40w rotella in it. is a new symptom. boat is in florida but I do have block heaters. that start up was after a week but I ran the boat and had no problem making power it seemed. batteries are new (2 weeks old). the starboard engine starts almost immediately. the port was always a crank rotation slower but now it seems im leaning on the starter for a good 10-15 seconds to get it to turn over. I do my fuel filter and oil changes regularly.
  5. Capt Ralph

    Capt Ralph Senior Member

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    Try the heater and see if it helps next start.
    Problem before the battery replacement?
    Battery cables tested?

    Were in Jax. Down to 30 last Monday morning.
    Yep, we like block heaters.
  6. Pascal

    Pascal Senior Member

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    DD needs compression to fire up... if your starter is slow, you may have to crank longer which coudo results in unburned fuel leaving a sheen. Before pulling the starter, check for corrosion on batt cabke and try paralleling
  7. Capt J

    Capt J Senior Member

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    Are you saying the starter is turning the motor over slower than the stbd? If that is the case, you're going to need to diagnose why it's turning over slower. Check batteries first (most likely culprit), cables second, starter third. If those all check out, it could be a leaking injector filling a cylinder or something else. I had an 8v92 low hour boat but sat on a river with a lot of current. Used to have to roll both motors over 30-45 seconds before they'd fire, then smoke a ton of grey smoke for several minutes then ran clean (DDECs). They seemed to perform ok also. Turns out each motor had a dead cylinder from sitting with the exhaust valves open and the current pushing salty air up there. This would be the extreme scenario.
  8. Lepke

    Lepke Member

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    I've been running 671s since the early 1960s. Usually when twins crank differently, it's electrical. Besides the battery and cabling, the solenoid can have contacts that are making a poor connection. There are two lugs where the battery cable and the starter motor connect. They contact a copper disk the rotates slightly each start. Eventually, long starts cause burning and pits on the lugs and disk. If you're ambitious, you can disassemble the solenoid and file ends of the lugs and disk to like new and restore the ability to transmit full amps to the start motor.
    With the engines warm and running under power, you can use a hand temperature measuring gun to read the temps at the exhaust ports and get a good idea of the cylinder conditions. One cylinder running cold could indicate a problem with the rings, valves or injector in that cylinder.

    Attached Files:

  9. Boomer

    Boomer Member

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    Had the same issue on another motor..rack was out of tune
  10. Capt Ralph

    Capt Ralph Senior Member

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    update?
  11. Boomer

    Boomer Member

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    Vroom vroom!!
  12. cleanslate

    cleanslate Member

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    Will the rack being out of tune/adjustment cause slow rotation and hard start in summertime weather conditions ? mine are 471 TI J and T 1981.
  13. Posterboy91

    Posterboy91 New Member

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    my issue seemed to subside on its own with using the boat more often. I am still having a tech come back to the boat and check everything. sorry for not responding in a week the boat had a vibration still after I got it back from the yard so I had to bring it back up there and have them pull it out again. the other reason I would think was slowing the motor down from starting was it was 55 degrees out and I hadn't started the boat in a few weeks. after I have the techs come out and go over the boat I will update everyone with their findings.
  14. cleanslate

    cleanslate Member

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    Ok, well 55 degrees will do it, and I'm sure the motors were colder than that. It takes a day or three of warmer weather for them to come up to current ambient temperature ,such as 65 degrees etc. Those engine blocks are thick and heavy! and hold the cold.
  15. Posterboy91

    Posterboy91 New Member

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    went to the boat today and see oil coming out of my starboard engine airsep. the port engine was the one having a had time starting so its unrelated to the original topic. this engine starts everytime with out hesitasion but I took the boat from Hillsboro inlet outside it felt down on power but I could still cruise at 2000 but it wouldn't push over 2100 where the port engine kept climbing in rpm as it should. could it be the turbo seals or something more serious internally.
  16. Capt J

    Capt J Senior Member

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    You need to get a good Detroit diesel mechanic out who can put his ears, eyes, and hands on these engines and figure out what exactly is going on with them.
  17. Posterboy91

    Posterboy91 New Member

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    any suggestions
  18. Posterboy91

    Posterboy91 New Member

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    do you have any Detroit mechanics that you trust of have used in the past in fort Lauderdale area
  19. Capt J

    Capt J Senior Member

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    While not a Detroit specific Shop, call N+G engineering in Hollywood, FL. Otherwise the dealer FDDA and RPM diesel are both good. They are good with them. I haven't messed with anything major with a Detroit in over 5 years.

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