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Fuel injector/injection question?

Discussion in 'The Okie Corral' started by Adjuster, Apr 22, 2013.

  1. This is in regards to a boat outboard motor but I would think the same situation would apply to any fuel injected engine. If you have a stuck open or closed injector on a 4 cylinder engine will it cause 1 or more of the other injectors in the series to not function because its not getting the correct signal from the stuck injector? I am talking about a stuck injector where the solenoid is froze up, not a clogged spray injector.


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  2. John Rambo

    John Rambo Raven

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    No

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  3. MaxxAction

    MaxxAction

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    No...

    the injectors all operate independent of each other. I don't know how it is controlled on a boat motor, but on a car motor, it is determined by a CAS (cam or crank angle sensor) that every time the CAS tells them to,(based on a magnetic or light pulse) the injectors fire.

    If the CAS is bad, then none of them will fire.
     
  4. When there is no power to an injector, holding it in your hand for instance. Is it opened or closed?



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  5. HollowHead

    HollowHead Firm member

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    I know nothing of outboards but if it has EFI, it must also have an ECM. ECMs usually can be scanned for a DTC. HH
     
  6. Unpowered, it should be closed.

    -Pat
     
  7. MaxxAction

    MaxxAction

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    Also...

    be cautious. Pull that plug and make sure it isn't stuck open by verifying that the cylinder isn't full of fuel. If it is blowing wide open it can fill the cylinder with fuel and destroy the ring seat with the cylinder wall, or worse yet hydro lock and bend a rod.
     
  8. The injectors are controlled individually, so one dead injector will not prevent other injectors from firing.

    However, the oxygen contents in the exhaust gas is measured for all cylinders together (or for a bank of cylinders in a V8). That means a bad injector will affect the fuel mixture in other cylinders, making them run too rich or too lean.
     
    Last edited: Apr 22, 2013
  9. HollowHead

    HollowHead Firm member

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    This. You can do a poorman's diagnosis by checking resistance across the trigger wires (should be closed) and then hooking a 12VDC source to them (injector should "click"). This can be done with the injector installed. HH

    Edited to add: don't hold current to the injector any longer than necessary. Depending on its duty cycle you can fry it.
     
    Last edited: Apr 22, 2013
  10. Ok sounds like you guys know what you're talking about so here is the full story. 2005 or so Yamaha 4 cylinder. 5 days prior it was out fishing and running fine. Tried to start the motor and it would not run or even fire zip nada nothing just starter turn over. We called a mechanic to come to the house and diagnose. He says gelled fuel and two frozen injectors the typical ethanol problem that is killing all boats $600.00 repair quote we pay $100.00 for his diagnosis and send him on his way. We decide to see if we can get it running without the mechanic repair. So we flush all the old fuel out of the engine and hook up an external fuel tank with new fuel and flush it through the engine. Hook the new fuel back up to the fuel rail and nothing it will not fire. I unplug all injectors so I have 4 pigtails in my hand. Using a noid light I test each pigtail individually as the engine is cranked and each pigtail pulses indicating that it is getting the correct electrical signal as it should. Then I plug in injector #1 and test the other pigtails, now injector #3 is a solid light as if its getting constant power but #2 and #4 appear to be correct. So I unplug #1 and everything is back to normal. I plug in #2 and test the other pigtails now #1 and #3 is correct but #4 is solid light. Somehow I think the injectors being stuck are short circuiting their opposing or companion injector. I am not a mechanic, just a handy guy but I sure learned a lot about boat motors messing with this problem. So here is what I think is happening. A stuck injector somehow sends the wrong signal to its opposing injector causing them both to be stuck. Or the computer on this engine is fried sending all wrong signals to the injectors. I checked all the engine wiring for a short but could find nothing. Our next plan of action is to send off all 4 injectors to be cleaned/rebuilt and tested at a cost of $25.00 each. What do you guys think? By the way the motor turns over and runs fine if we spray a little gas or starter fluid into the injector holes so its getting spark at the plugs, that all checks out.


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  11. I would not condemn the injectors based on your test light reading. It may be normal, depending on how exactly the injectors are driven. (I am not familliar with your motor, so it's just a guess.)

    Do you have proper fuel pressure in the rail?
     
  12. MaxxAction

    MaxxAction

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    Yeah....

    most newer motors have injectors with internal components that are tolerant of ethanol. However, some older ones are not.

    You can also use an ohm meter to check the resistance of the injector to help you diagnose. I am sure you can find the specs online pretty quick.
     
  13. HollowHead

    HollowHead Firm member

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    Agreed. My expertise is with motorcycles and what Adjuster describes happens with long storage bikes often. E-85 destroys engines, but that's for another thread... HH
     
  14. We didn't gauge test the pressure but it shoots out a stream the size of my finger about 5 feet so it looks good.


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  15. Depending on how the ECM operates, one injector can cause problems with others. If an injector shorts, the circuit will short to ground. Most injectors have constant power and are controlled with ground. If your engine is a two stroke, or a batch-fire four stroke, there will be other injectors on that circuit and they will show a short to ground with a noid light as well.
     
  16. HollowHead

    HollowHead Firm member

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    I'll take a wild guess that it probably has either Keihen, Delphi or Bosch EFI and aftermarket injectors are a hellova lot cheaper than OEM. If you're going to replace them, bring the old ones to a shop that sells Parts Unlimited, Inc and see if they cross to motorcycle, personal watercraft or ATV/snowmobile injectors... HH
     
  17. Well, if you have spark and fuel pressure... It must be either the injectors or the ECU. I would say you need to find a mechanic with proper test equipment before you start spending money on swapping parts that may or may not be bad.
     
  18. boozer

    boozer

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    I'm with "batch fire", if one of a pair of injectors is shorted, the other will be affected.

    You did a good diagnostic with the noid lights, the rest is a little confusing, but I think you are on the right track.
     
  19. XshooterX

    XshooterX

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    Did the mech not have diagnostic equipment? (Code reader) if not, just have that done. Some problems are not diagnosed easily, even with codes, but fuel problems are usually pretty well broken down.


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