Truck TBI for Marine Use?

Discussion in 'Gas Engines' started by wufibugs, Apr 21, 2017.

  1. wufibugs
    Joined: Apr 2017
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Chula Vista, CA

    wufibugs New Member

    82 Bayliner 2350. Replacing the Volvo Penta 5.0 carb with a 5.7 vortec out of a 98 Chevy Suburban. These have throttle body spider fuel injection.
    I was reading a thread from January 2007 in which several senior members [beech & stonebreaker] seem to say that this fuel injection system [ECM reprogrammed] can be used in the marine environment. Other forums claim they are too dangerous and I have to get a marine designed TBI injection system. I'm not at all clear on how the marine version differs or if it does.

    Seems as though spider injection system should be safe because it is fully sealed. Since I will not be using the EGR, EVAP, or PCV systems the only opening in the intake system is the throttle body in the upper manifold and that meters air, not air/fuel. I'm just not sure I see where this system poses any greater hazard than any gas engine in an enclosed space.

    The stock distributor is entirely sealed as are the starter and alternator.
  2. gonzo
    Joined: Aug 2002
    Posts: 16,778
    Likes: 1,703, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Marine fuel injection systems have the pump at the engine, and the fumes are vented into the intake. Automotive systems have a pump at the tank and a safety vent to the atmosphere. The main safety issue is having a pressurized fuel line from the tank to the engine. That also will require you install an automotive tank or modify a marine one. Also, you need to check that relays, etc. are spark proof and don't have open vents.
  3. PAR
    Joined: Nov 2003
    Posts: 19,126
    Likes: 497, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Additionally the spider MPI system was mroblemmatic at best and didn't last long in production as a result. Marine versions ofthisgeneration Vortec used a CFI assembly, not the MPI (spider) setup.
  4. wufibugs
    Joined: Apr 2017
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Chula Vista, CA

    wufibugs New Member

    Gonzo, I would not even attempt to modify the tank to accept an in-tank pump. I am going to use an external high pressure fuel pump that can be mounted closer to the engine and I will use stainless flexible fuel lines to mate to the stainless rigid line that was stock on this motor. No matter what system is used, there's always going to be a fuel line from the tank to the point of fuel delivery. Seems to me that carbs, with their fuel bowls and fuel/air mixing chambers, the spark arrestor is much more likely to be tested than in the spider system where fuel is fed to a sealed chamber containing the injectors which are fully sealed to the point of combustion.

    Par, I did some research on the reliability of spider injection and found the following:

    "the early style Central Sequential Fuel Injection (CSFI) or Spider units tend to fail overtime. This is mainly due to the poppet valves becoming plugged with carbon deposits. Some symptoms of a bad poppet valve are hard starting, due to a leaking poppet valve, misfire codes, rough idle, loss of power and performance and a noticeable decrease in fuel economy. [that's because of the way] the Poppet valve seats in the intake. The tip of the poppet valve conducts a large amount of heat allowing for carbon to build up on the tip of the valve. . . . new design [MPFI] installed in the same exact intake manifold. the nozzle of the injector is recessed away from the intake valve. The plastic pintle tube acts as an insulator to the injector tip which decreases the amount of carbon that's able to develop on the end of the injector."

    My motor has the newer style poppet. By eliminating the PCV and EGR I will not be running unburned oil/gas through the intake which should reduce [not eliminate, of course] carbon buildup of which the article speaks. Also, unlike cars, boat engines run cooler and at steady high rpms so the carbon buildup from low speed and idling should not be as severe. The final element is fuel metering. If the ECM was properly reprogrammed, as I'm praying it was, the motor should not run rich, which should help. Unfortunately, that's the hardest element to control because there are no O2 sensors for the ECM to react to.
  5. missinginaction
    Joined: Aug 2007
    Posts: 1,103
    Likes: 254, Points: 83, Legacy Rep: 512
    Location: New York

    missinginaction Senior Member

    I have one of these injection systems in a 1996 Chevrolet Suburban. This vehicle is 21 years old and has traveled about 193,000 miles. I never had a single engine issue, save for a leaky intake manifold gasket when the vehicle was still under warranty.
    Just this past winter the engine became just a little hard starting when it was warm. We determined that the injector(s) were beginning to leak a bit after the engine was shut down and this caused an over rich condition when the vehicle was restarted. For instance if you stopped for 10 minutes, no problem. If you stopped for an hour or two, the engine would still be warm but fuel would have time to leak into the cylinders a bit. Thus that flooding feeling.
    Cold starts, never a problem. Runs fine, no codes.
    At this point, I'm not even thinking of fixing it, hopefully the problem won't get any worse.
    I've found this engine to be very reliable.
  6. gonzo
    Joined: Aug 2002
    Posts: 16,778
    Likes: 1,703, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Marine pumps have vents that go into the intake and not the atmosphere as automotive types do.

  7. Ike
    Joined: Apr 2006
    Posts: 2,667
    Likes: 467, Points: 83, Legacy Rep: 1669
    Location: Washington

    Ike Senior Member

    The primary issue here is modifying the engine to meet marine standards. Starters, alternators, and other electrical equipment have to be ignition protected. (no sparks to ignite fuel vapors) fuel pumps are required to be within 12 inches of the fuel inlet on the engine, so it has to be either mounted on the engine or close by. You would also have to find some way to deal with the excess fuel that on an automotive engine flows back to the tank. This line is not allowed to be under positive pressure. Some marine engine manufactures use a gravity feed, others have a separate small tank to collect the excess and it gets recirculated.

    Then there is the issue of duty cycle. The duty cycle is different for a marine engine, so you would have to modify the ECM software. Marine engines run under a heavy load constantly (much like trucks) but do not have transmissions. So no shift points. They typically accelerate up to three quarter throttle (or full throttle if your one of those) and then run for long periods at about 3/4.

    As gonzo said marine fuel pumps cannot leak into the boat. If they develop a leak there must be some means of containing it so you would need a marine fuel pump.

    It can be done but it is usually cheaper to just buy a marine engine.
Similar Threads
  1. Poohbair
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.