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Lack of Turbo Boost

Discussion in 'Technical Discussion' started by Jimbo1959, Aug 26, 2014.

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  1. Jimbo1959, Aug 26, 2014
    #1
    Jimbo1959

    Jimbo1959 Member

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    Let me just sorry for the length of this post but I thought it best to put as much info out as possible. Just fired up 2 8V-92 TA DDEC II 760 HP. After some ecm problems took boat for a ride. Both engines fall flat on there asses. No turbo boost. 1 engine is rebuilt and the other engine is original. All 4 turbos were rebuilt. I added a gauge to the air box and a gauge to the air horn. Also fuel pressure and no load rpm, both good. Fuel psi 70 psi and no load 2400 rpm. Air box pressure at the dock was 10 psi, psi from blower.

    Took boat out again after connecting regulated air supply to TBS sensor. Boat would not pull past 1200 rpm, full throttle. Added 10 psi to TBS and engine woke up, as i increased psi to TBS engine rpm came up and turbos began to spool up, psi at air horn increased to 10 psi before we had to shut down. Problem is no boost.

    Here is my question all four turbos were rebuilt. The rebuilder said that the turbine wheels were approx 1/4 in to small in the exhaust housing, he replaced them with what he thought Garrett would use bigger. Would the smaller wheels spool faster and does anybody believe SS Diesel would have changed them?
    Thanks Jim
  2. Capt J, Aug 26, 2014
    #2
    Capt J

    Capt J Senior Member

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    I've seen the various mariniziers do weird things from time to time. I'm not knowledgable to help you with your situation, but anything is possible with Turbo's. I would call Garrett and ask them. Perhaps the turbo's need some "blowby" on the turbines to allow the engines to spin up or some weird thing.
  3. Capt Ralph, Aug 27, 2014
    #3
    Capt Ralph

    Capt Ralph Senior Member

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    thinking out loud

    Your emg shutdown flappers are wide open. Throttle delays and rack are not binding. Your hull bottom is clean. You did not add new air filters.

    Would a DDEC eng allow for over fuel? what color is your exhaust?

    Please don't take this as a S A response but it has to be commented on;
    The turbos worked before and then modified. Now no boost pressure. Hummm.
  4. Jimbo1959, Aug 27, 2014
    #4
    Jimbo1959

    Jimbo1959 Member

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    EMG shut down flappers open. No racks or governor adjustments, Engine is controlled electronically. Exhaust is clear, no smoke at at all unless I manually add air to the turbo boost sensor. The new owner bought the boat as repo, the starboard engine was full of coolant and the port engine would not start. Boat was towed to shop.
    Thanks Jim
  5. Capt J, Aug 27, 2014
    #5
    Capt J

    Capt J Senior Member

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    Generally from what I've seen turbo's on Detroits don't make any boost to speak of at 1200 rpms. Maybe 1-2 psi or so. Generally I hear the turbo's starting to build boost around 1350rpms. That being said you're in a tough situation because you had nothing to baseline the boat and engines with. How is the bottom condition and propellors? If the boat is way overpropped or covered with growth it's possible the load factors are too high for the boat to accelerate to enough rpms for the turbo's to make boost. If the bottom is clean, I would definately look at the turbo's. I would try to talk to someone from S+S if you can, garrett and so forth. It might be possibly that the turbo wheels were intentionally smaller to allow some of the exhaust to bypass and possibly allow the motors to breathe better on acceleration until the turbo's start providing boost. This I don't know, I'm just thinking out loud. What condition were the old turbine wheels in and is it possible to put them back in the turbo's and try it......although this is a heck of a lot of work to just try it. Can you look at the factory turbo's and see what turbine wheel they're spec'ed with? It also can be an issue with a sensor and the computers allowing the injectors to provide more fuel or enough fuel.
  6. Jimbo1959, Aug 27, 2014
    #6
    Jimbo1959

    Jimbo1959 Member

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    Well I think I got it figured out. Tried calling Garrett, no help. Called another turbo shop in So Cal. Told him what problem I was having, told him what the other rebuilder did. He said this engine particularly the DDEC needs to have the smaller wheels installed. He explained to me, that essentially I'm trying to spool up these bigger wheeled turbos with a 4 cylinder engine. These large wheeled turbos (1 only) would work fine on an engine exhaust system that combines both cylinder banks. I had the original exhaust wheels and after I pulled off the new rebuilds, it is very evident in the size difference. So we sent them back with the original wheels.
    Thanks Jim
  7. Old Phart, Aug 27, 2014
    #7
    Old Phart

    Old Phart Senior Member

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    I dunno






    All righty, then.

    All's well that ends well.
  8. Jimbo1959, Aug 31, 2014
    #8
    Jimbo1959

    Jimbo1959 Member

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    actual wheel difference

    Picture of wheel size difference. 20140827_123243.jpg
  9. Capt Ralph, Sep 19, 2014
    #9
    Capt Ralph

    Capt Ralph Senior Member

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    Was there any follow up or comments after you put it together again?