How to Check for a Leaking Fuel Injector
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Cadillac Tech Tips - How to fix it Discussion, How to Check for a Leaking Fuel Injector in Item Specific Cadillac Discussion; If you suspect a leaking fuel injector(s) you must remove all the fuel rail hold downs then lift the rail ...
  1. #1
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    How to Check for a Leaking Fuel Injector

    If you suspect a leaking fuel injector(s) you must remove all the fuel rail hold downs then lift the rail with the injectors still attached (electrial connectors need not be attached). Turn the key ON to pressurize the fuel system but DO NOT crank the engine. Then simply look at the tips for leakage. If you suspect a clogged injector(s) you can crank the engine (electrical connectors must be connected in this case) and watch for one or more that are not spraying fuel.
    CAUTION:
    They will be spraying atomized fuel so put out your cigarette, move the trouble light Do it on a cool engine and don't do it while :drinker

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  3. #2
    EldoGlo is offline Cadillac Owners Member
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    Re: How to Check for a Leaking Fuel Injector

    Sorry Ranger I'm confused, with the fuel rail off and still connected to the fuel injectors, are the injectors supposed to be removed from the vehicle? this leakage you refer to is it like a faucet drip that drips constantly and needs a new washer? (and this is done with key in on position, not cranking)If this is so then I have a leaky injector and need to replace it. Right? If there is no leakage then it may be a clogged injector. Right? If there is a sign of a clogged injector I would test it by removing it from the vehicle along with the removed fuel rail, and then crank the engine over and look for the injector not spraying fuel from it, Right? if there is one or more not spraying fuel I need to replace the injector right? Would there be any electrical related problem associated with the wiring that would cause a faulty injector and if so how would you check for this? sorry for being so stupid but you guys are really great!

  4. #3
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: How to Check for a Leaking Fuel Injector

    Sorry Ranger I'm confused, with the fuel rail off and still connected to the fuel injectors, are the injectors supposed to be removed from the vehicle?
    Yes, the injectors and rail are lifted as one unit. That removes the injectors from the ports.

    this leakage you refer to is it like a faucet drip that drips constantly and needs a new washer?
    I guess it could be a drip or a spray depending on how bad it is.

    (and this is done with key in on position, not cranking)If this is so then I have a leaky injector and need to replace it. Right?
    Yes.

    If there is no leakage then it may be a clogged injector. Right?
    No, there should be no leakage with the system pressurized and the engine not cranking. No call for fuel from the PCM. Much like turning your faucet off, the pipes (fuel system) are pressurized but the faucet (injector) is off so there should be no water (fuel) leaking.

    If there is a sign of a clogged injector I would test it by removing it from the vehicle along with the removed fuel rail, and then crank the engine over and look for the injector not spraying fuel from it, Right?
    Correct.

    if there is one or more not spraying fuel I need to replace the injector right?
    Correct.

    Would there be any electrical related problem associated with the wiring that would cause a faulty injector and if so how would you check for this?
    Yes, there can be. If the injector is not receiving a pulse signal from the PCM because of an open circuit or a bad PCM, the injector will not pulse. To check that you need a noid light that plugs in to the injector connector in place of the injector. They are not expensive. If it flashes then there is a signal there. You can't use a regular 12v test light. I am not sure why but it will not work. Been there, done that.
    One easy way to tell if the injector is operating is to use a stethescope. Place the tip on the injector body and you can clearly hear the injector pulsing.

  5. #4
    eldorado1 is offline Cadillac Owners Connoisseur
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    Exclamation Re: How to Check for a Leaking Fuel Injector

    I forsee a scenario playing in my head.

    DIY person is trying to diagnose a clogged injector. They remove the fuel rail, pressurize it, and see no fuel. Then they follow your advice, and try cranking it. Fuel sprays everywhere, and fuel vapors (being heavier than air) collect around the currently running (read: sparking) starter. FWOOSH! Person no longer has hair and/or life.

    Fuel is dangerous, and should be treated with respect. Not knocking you Ranger, nothing personal at all. But when unsafe practices are told to "newbies", I've got to step in.

    So, how do you test injectors? Whether they are sticking, or leaking?

    Well actually, it's pretty simple. What you need is an "injector tester". GM calls it the J39021. You can find ones that work similar to it on ebay, and the like, and typically cost between $80-$300. They look like this:



    I haven't found a place that rents them yet, but I'm sure SOME place out there will yet you borrow one. Autozone and Advance Auto do not however.

    Anywho, once you have one, the directions are simple to follow. What you do is connect a fuel pressure gauge to the shraeder port (on the fuel rail), pressurize the rail (I don't know how this is done on the caddy, but it may be as simple as punching a few buttons on the instrument panel, or it may involve placing a jumper in the ALDL port) by turning on the fuel pump for a couple seconds, and seeing what it does.

    If it starts dropping really fast (like a couple PSI/sec), then you have a leaking injector(s), or a bad check valve. You can check for the leaky injector by removing the fuel rail (everything still connected, do NOT remove the fuel lines or anything, just unbolt it, and pull straight up). Repressurize if necessary, but you should see a steady drip if it is the injectors. If not you have other problems.

    NOW, assuming when you pressurized the fuel rail the first time, that it DIDN'T start droping, and held fairly steady, now you can use the injector tester. (reinstall the fuel rail now)

    The process is simple,
    1) Pressurize the fuel rail by energizing the fuel pump for a few seconds.
    2) wait 2 seconds for the reading to stabilize
    3) Record initial fuel pressure (should be about 39-45 psi)
    4) Connect injector tester, and push the test button.(This will pulse the injector for a set amount of time)
    5) When the injector stops clicking, immediately write down the fuel pressure (varies, could be 20psi or 30psi or so)
    6) goto 1, repeat for all injectors

    Now, average all the pressure drops you wrote down.

    Example -
    1) 20psi
    2) 21psi
    3) 23.5psi
    4) 22psi
    5) 21psi
    6) 20psi
    7) 21psi
    8) 18psi

    Average = 166.5/8 = 20.81
    Any value more than 1.5psi off from this average is considered "bad". So,
    Anything above 22.3 or below 19.3 psi is bad, and needs to be cleaned or replaced. In this case, #3 and #8 need to be replaced.

    Keep in mind it will take some extra effort to start, because your engine how has a healthy dose of raw gas in it's cylinders...

  6. #5
    davesdeville's Avatar
    davesdeville is offline Banned
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    Re: How to Check for a Leaking Fuel Injector

    This should come in handy tomorrow, my friends and I are suspicious of a leaky injector on a Taurus SHO we're rebuilding. Checking for a leaky one Rangers way is pretty obvious but I probably wouldn't have thought of it...

  7. #6
    Ghostsoldier's Avatar
    Ghostsoldier is offline Cadillac Owners Fanatic
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    Re: How to Check for a Leaking Fuel Injector

    Sorry for the necro-posting, but Ranger's idea worked perfectly...I've ruled out the injectors as a possible culprit in the Case of the Skipping Eldorado....
    Rob

  8. #7
    Eninety2 is offline Cadillac Owners Fanatic
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    Re: How to Check for a Leaking Fuel Injector

    I tried to pull the rail off today. How much force is needed? I pulled pretty hard and it didnt budge.

  9. #8
    Ghostsoldier's Avatar
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    Re: How to Check for a Leaking Fuel Injector

    You have to give it a severe tug, as the injector o-rings have a good grip; I started at one end, pulling them one by one, using both hands wrapped around the injector and fuel rail connection. You might be able to use a pry bar of sorts, but be very careful to distribute the force evenly, or you'll break the rail. What you want, is the injectors to come out of the ports, NOT out of the rail itself (there are o-rings on both ends of the injectors).

    Be sure to check that all the o-rings are still seated on the bottom lip of the injectors, as they have been known to pull free and remain in the injector port bore (as well as in the rail port, too).

    Rob

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