Mercruiser 4.3 cutting out

Discussion in 'Gas Engines' started by Claytos, Jul 9, 2013.

  1. Claytos
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    Claytos New Member

    Hi.
    I have a 2005 mercruiser 4.3 efi. It cuts out randomly but then either goes to idle or if it stalls, it restarts immediately every time. It can run for days or weeks with no problems but will then do this every few minutes. It seems to do it at any speed or revs above about 2000. This weekend it felt like it was losing power at the top end too - almost like it was starved of fuel. Has anyone seen anything like this ? Thanks.
     
  2. PAR
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    PAR Yacht Designer/Builder

    When was the last tuneup, does it receive regular maintenance, how often is it used, when was the fuel filter(s) changed? EFI systems are pretty reliable, have the fuel pressure checked and change the filters would be my first suggestions.
     
  3. Claytos
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    Claytos New Member

    It's just been serviced and the filters are clean. My current thoughts are that it feels more electrical than fuel - it cuts out instantly and restarts instantly.
     
  4. PAR
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    PAR Yacht Designer/Builder

    The EFI system is easy to diagnose on the 2005 Mercruiser, so have it looked at, because hunting and pecking at it, will only cause you to buy and replace things, you don't need. From the sound of your description, it's probably a fuel pump or fuel pressure regulator, though it could be as simple as a poor connection. Also look at the parts listed on your service report, to see if "all" of the fuel filters were replaced. I don't think it's a bad connection, though it could be. The symptom of it lacking power over 2k RPM, suggests the regulator or more commonly the pump. Simply put, you're getting fuel, just not enough at the levels necessary at higher RPM. This is my guess with the little information provided.
     
  5. Claytos
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    Claytos New Member

    Thanks for the replies. I'll try to clarify. The diagnostics don't show anything as most of the time the engine is running perfectly. The power loss that i mentioned is minute and barely noticable and only happens with the throttle fully open - i have only noticed that twice.
    The real problem is the total cut-outs of the engine. These happen in a split second but have never happened when idling. Sometimes the engine stays running when i throttle off and then runs straight back up to full throttle. Other times, it cuts out but always restarts first turn. Other days the boat runs perfectly all day with no problems at all.
     
  6. CDK
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    CDK retired engineer

    All EFI systems I have seen have a diagnostics plug that can tell a lot about engine health when connected to a simple dedicated computer or a laptop running the diagnostics program. Some are so advanced they keep a log of anything abnormal, others show only actual values.

    This seems serious enough to be registered in the EFI memory.
     
  7. thudpucker
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    thudpucker Senior Member

    How about something in the fuel tank stopping the flow?
    Maybe an 'open' on the engine suction side of the Fuel flow.
    Are your floor boards right on top the Fuel siphon outlet. Traffic may have cracked that bit of tubing and fitting right on top the tank.
     
  8. PAR
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    PAR Yacht Designer/Builder

    The 2005 Mercruiser EFI arrangement does store codes. It sounds like a fuel pump or pressure regulator, both are easy to test. Fuel pumps usually give you some warning before they die and these symptoms may be just that.
     
  9. thudpucker
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    thudpucker Senior Member

    If you are losing electricity, the engine just dies!
    If you are losing fuel you'll get some staggering and slowly dying.
     
  10. PAR
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    PAR Yacht Designer/Builder

    Not necessarily Thud. A loose battery terminal can cause some weird stuff, but it doesn't have to die. The same is true of the other circuits, unless you've popped a breaker or fusible link. The same is true of EFI fuel delivery. You can have sufficient enough pressure at idle and off idle speeds, but not quite enough over 2k RPM. There are other situations too. As a rule, bad or sloppy electrical connections don't get "better" just because you shut it down (it does it for you), especially at the irregular intervals. Most of the time it just get worse and worse, until one time, it don't start back up.
     
  11. thudpucker
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    thudpucker Senior Member

    I'm gonna be Ugly tonite and argue with Par.
    Fuel starvation (no matter how it happens) as long as you have Fire, will always show up and a dying by inches with staggering and popping back through the Intake.

    Anytime you lose ignition, it just dies. No popping etc.

    If you lose +12 at an Electric pump or fuel valve SOMETIMES that will cause a sudden quiet death.

    Don't these kind's of Post's make you wish you lived closer to the Victim so you could get the mystery solved quicker?
     
  12. Claytos
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    Claytos New Member

    Thanks for the replies - imappreciate the advice. I'll have a good look this weekend if the sun goes away. Otherwise, i'll keep pushing it in the hope that something actually breaks and makes it easier to find the fault :)
     
  13. PAR
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    PAR Yacht Designer/Builder

    You may regret your actions, as it might come true and you'll have a bigger bill. Yes, Thud, I do often wish it could spend 5 minutes in my yard. I'd probably (much like you) be able to figure it out in that time. Less time that it takes to type these points (I use my nose and one other finger).

    At this point it's all just guessing. It could be one or a combination of things, some simple, others not so much. It could be as simple as a fuel filter will a hunk of crap in it, that occasionally restricts or stops flow, so the engine sputters or dies. When the engine is turned off, the systems leaks down a bit and the hunk of crud falls away from whatever it's blocking. It also could be schizophrenic ECM.

    If it was my boat, I'd level the playing field and do a compressive tune up and replace all the consumables, tossing a new cap, rotor and wires on too, just to know the quality of these pieces as well. This way you know how old the filters, the wires, the plugs, etc. are and much of the guess work can be eliminated. I do this with all used boats that are new to me. I consider it just the cost of the purchase.
     

  14. thudpucker
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    thudpucker Senior Member

    I had an EFI 4.3 in an Astro Van. I loved it.
    But working on it was a real pain because it was in that Van, half in and half out.

    The second time it gave me trouble, acting different each time, I was smart enough not to buy another Computer for it. Like I did the first time.

    Yessireeebob, the second time it acted up, I changed Plugs and she came right up and ran for another 90,000 in Louisiana.

    Went to Alaska and back at least two times.
    It was a GREAT engine.
    But when it was a Bad engine, I was verry verrry dificult to troubleshoot.
     
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