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How to identify a leaking fuel injector

This is a discussion on How to identify a leaking fuel injector within the Technical / Maintenance forums, part of the General Discussion category; Can anyone tell me the easiest way to tell if I have a leaking fuel injector, and of course which ...

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    Registered User itbrian's Avatar
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    How to identify a leaking fuel injector


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    Can anyone tell me the easiest way to tell if I have a leaking fuel injector, and of course which one it is?

    The engine in question is a 2003 6.0 liter gas engine.

    I've been experiencing hard warm engine starts for close to 2 years now. Starts fine when the engine is cold, but when warm, and has sat for 30 minutes or so, it takes 3 attempts of cranking before it starts, where it then stumbles, almost stalls, and then is ok.
    Sometimes it starts on the 2nd or 3rd attempt without stumbling, itís about 50/50.
    It drives great, with no noticeable loss of power.

    I've tuned it up, replaced the fuel filter, and just today I replaced the fuel pressure regulator and the problem still exists.

    I'm now wondering if itís a leaking fuel injector.
    BTW, itís not throwing any codes!
    Help me if you can!!!
    2001 Tahoe LT 5.3L (Sold)
    2003 Silverado 2500HD Regular Cab, 6.0L (Sold)
    2003 Silverado 1500 LT ext. cab with QUADRASTEER!!!

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    Master Certified Tech performabuilt2's Avatar
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    Re: How to identify a leaking fuel injector

    with a scan tool kill the injector and watch the data stram fuel trims when you kill the leaking injector the trims should t change all that much as with the good injectors. you can also look at a fuel pressure guage and unplug the injectors you should see a pressure rise when you unplug the injectors except the one leaking may want to try cleaning the throttle body and cleaning the IAC if it doesnt have electronic throttle.also the fuel trim on the leaking bank will be an extreme negative percent if leakin injector becuase ite trying to cut back on fuel
    Last edited by performabuilt2; 03-09-2008 at 10:08 PM.
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    Registered User itbrian's Avatar
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    Re: How to identify a leaking fuel injector

    Thanks for the quick reply performabuilt2,

    I don't know that my Actron CP9180 scanner will do that.
    Then again I just recently got it and have only used it for checking for codes, guess I better get the manual or CD and find out how to get to that screen.

    Are you talking about the common scanner that sells for about $150-$200?

    I may have better luck with the fuel pressure gauge test.

    I'll give that a try.

    Thanks again,
    Brian
    2001 Tahoe LT 5.3L (Sold)
    2003 Silverado 2500HD Regular Cab, 6.0L (Sold)
    2003 Silverado 1500 LT ext. cab with QUADRASTEER!!!

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    Re: How to identify a leaking fuel injector

    Before you start throwing parts at it.............

    Check the fuel pressure regulator ! Easy and fast!
    Start engine let run.......Shut off
    Pull vacuum line off. If wet with fuel its bad!

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    Re: How to identify a leaking fuel injector

    You might have to drive it around for a while to burn up all of the fuel the leaked into the vaccuum system.

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    Registered User itbrian's Avatar
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    Re: How to identify a leaking fuel injector

    Sonjaab,
    I just replaced the FPR, maybe you missed that part in my post, but I will check the new one to see if it's leaking gas from the tube.

    Whitextreme,
    Being that it is my work truck, I don't use it much this time of the year. But after I replaced the FPR I took it for a 30 minute drive on the highway, going between 70 - 80 mph.

    Then parked it and let it sit for a 1/2 hour, and of course the hard warm start condition still was there. I would think that was a long enough drive to clear any fuel left in the vacuum system. Don't ya think?
    2001 Tahoe LT 5.3L (Sold)
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    Re: How to identify a leaking fuel injector

    Sorry I did miss the replaced FPR part............

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    Re: How to identify a leaking fuel injector

    If I were looking for a leaky fuel injector (or any number of other fuel delivery problems), I would probably start by putting a fuel pressure gauge on it. Run the fuel pump to pressure the system up, then shut the pump off and watch the pressure gauge. It should hold pressure. If it does hold pressure, then I know can be fairly confident it isn't a leaky injector (or other leak in the fuel system). If the pressure bleeds off quickly, then something is leaking somewhere, and I can proceed to investigate and find out where it's leaking/bleeding off.

    While I had the pressure gauge on, I'd check to see what the fuel pressure was while trying to start: especially when it's hard to start.
    Last edited by MrShorty; 03-10-2008 at 09:04 PM.
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    Re: How to identify a leaking fuel injector

    Check the number 7 injector REALLY good. Common failure at my shop. Actually had to change the number 7 rod cause it was twisted form fuel overload into the cylinder. The best way is to do a fuel injector drop test.
    ASE Master Technician / L1

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    Registered User R20Mike's Avatar
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    Re: How to identify a leaking fuel injector

    If you dont have the tool / scaner to do some of the test mentioned check your plugs......you should be able to find a "rich" one

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    Re: How to identify a leaking fuel injector

    Ok, the fuel pressure gauge test is next and I'll post the results. But I have to go buy a new fuel pressure gauge, the one I have is a combo fuel pressure and vacuum gauge about 20 years old, I don't think that will work on this engine!

    I don't suppose a scanner tool reads the fuel pressure.

    Maybe I'll check the plugs first, I assume it's best to do right after a hard start, correct?

    OLDBLACKIE, what's a fuel injector drop test?
    Do you just disconnect one at a time and listen for no change when the bad one is disconnected because it's still leaking fuel into the cylinder?

    Thanks for the suggestions everyone!!!
    Last edited by itbrian; 03-11-2008 at 07:15 AM.
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    Re: How to identify a leaking fuel injector

    The drop test is where you hook up a good fuel pressure gauge and turn the fuel pump on by cycling the key on and then energize one injector. take a reading before and after energizing the injector. repeat this on all 8 injectors. It is best if you use a tool for turning on the injectors, some times a scan tool will let you do it but most of the time they will not. I know that NAPA sells the injector tester that is where I bought mine.
    ASE Master Technician / L1

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    Registered User masintenn's Avatar
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    Re: How to identify a leaking fuel injector

    Quote Originally Posted by OLDBLACKIE
    The drop test is where you hook up a good fuel pressure gauge and turn the fuel pump on by cycling the key on and then energize one injector. take a reading before and after energizing the injector. repeat this on all 8 injectors. It is best if you use a tool for turning on the injectors, some times a scan tool will let you do it but most of the time they will not. I know that NAPA sells the injector tester that is where I bought mine.
    Due to the fuel rail setup, wouldn't the leaking injector allow the pressure to leak down regardless of which one is energized?
    Last edited by masintenn; 03-11-2008 at 08:40 PM.


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    Re: How to identify a leaking fuel injector

    Quote Originally Posted by masintenn
    Due to the fuel rail setup, wouldn't the leaking injector allow the pressure to leak down regardless of which one is leaking?
    yes it will. i just replaced all 8 of mine with the ford/bosch set from www.fiveomotorsports.com. i had one or more leaking, and the only way i could tell was when i had the upper intake off, look into the hole of each injector after cycling the key, and you could see them leaking. 5 of them were, and the ford set are a better design, and loads cheaper than o.e.m. the swap woke my truck up a ton, and cured the hard start completely! good luck, brian

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    Registered User itbrian's Avatar
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    Re: How to identify a leaking fuel injector

    Another tech told me the best way to see if you have any leaking injectors is to remove the fuel rail, leave the injectors securely connected, and energize the fuel pump (turn the key on) and look for any leaking injectors.

    It seems easy enough, but how difficult is it to remove the fuel rail???
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    slammed dually owner brianbgboy's Avatar
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    Re: How to identify a leaking fuel injector

    you have to remove the upper intake, and unbolt the fuel rail. it is a little tricky, but if you get in that far, you may as well replace the injectors. if you have 2 leakers, new ones will cost what the bosch replacment set of 8 will cost. and you can bet the oem ones will leak again!!

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    Registered User masintenn's Avatar
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    Re: How to identify a leaking fuel injector

    Sorry if anyone feels this is a thread jack......

    I've had this same hard starting / engine warm problem on my commuter / crapper / cavalier ever since I replaced an externally leaking injector. I've replaced the o-ring set to no avail. This car has a side feed injector setup which is super crappy. I have a hard time believing the injector is leaking and tend to think the new injector somehow has a richer "start up pulse." But I know it's a problem with too much gas because pumping the gas pedal starts it every time and the car idles and runs perfectly.....so I'll probably never try to fix it!


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    Registered User itbrian's Avatar
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    Re: How to identify a leaking fuel injector

    OLDBLACKIE,
    Are you an ASE Master Technition or Technician?

    Sorry, I couldn't resist!!!
    2001 Tahoe LT 5.3L (Sold)
    2003 Silverado 2500HD Regular Cab, 6.0L (Sold)
    2003 Silverado 1500 LT ext. cab with QUADRASTEER!!!

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    Re: How to identify a leaking fuel injector

    I"m with Brian on this one. Since you've done the FPR, it's time for the injectors. I had your exact same problems, and the Bosch injectors solved it. You can get the same thing from your local parts store, just ask for injectors for a 5.0 Mustang. (assuming OE in your engine are 19lb/hr rating)

    I got mine from fiveomotorsports too though
    Last edited by skills4lou; 03-12-2008 at 04:30 AM.
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    Re: How to identify a leaking fuel injector

    Quote Originally Posted by masintenn
    Due to the fuel rail setup, wouldn't the leaking injector allow the pressure to leak down regardless of which one is energized?

    one will leak down less than all the rest. thats your bad injector. the problem is if you have one leaking and one a little plugged, theyll both be low.

    Quote Originally Posted by brianbgboy
    you have to remove the upper intake, and unbolt the fuel rail. it is a little tricky, but if you get in that far, you may as well replace the injectors. if you have 2 leakers, new ones will cost what the bosch replacment set of 8 will cost. and you can bet the oem ones will leak again!!
    no, you dont have to remove the upper intake. remove the engine cover and 4 10mm (IIRC) bolts and lift the injectors enough to see them. make sure youve got all the orings, and a little silicone dielectric will help them go in easier. but i wouldnt even do that until you KNOW its an injector.

    dont start throwing parts at it just because others have suggested. before you know it youll have a new set of injectors, a lighter wallet and a hard starting truck.

    fuel pressure IS the first place to start. check the pressure leakdown like other have suggested. if youve got a leakdown, isolate it by gently crimping off the pressure line. if it stops leaking down, its probablyfuel pump time. if it still leaks, its an injector (or the new regulator is bad, which is a possibility). post what you find and we'll go from there.
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