How to find the leaky injector
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HT4100 4.1, 4.5, 4.9 Discussion, How to find the leaky injector in Cadillac Engine Technical Discussion; On a 4.9 (93 deville) what is the easiest/best way to find a leaky injector ? I have come to ...
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    up2ng's Avatar
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    Lightbulb Increasing MPG, How to find the leaky injector

    On a 4.9 (93 deville) what is the easiest/best way to find a leaky injector ?

    I have come to this conclusion while on a search for better gas mileage. I have checked the FPR and there isn't a leak, there aren't any vacuum leaks, I have changed air filter, plugs, wires, cap, rotor, cleaned the EGR (TB side and intake holes), changed the O2 sensor (no signal) and PCV. Engine temp is always between 91 - 100 and the 02 sensor reads between .05 - .80 at idle (600-620 rpm). If I start the car when the engine is warm the idle will pulse about every 2 seconds for around 30 seconds. No problems cold starting, it has never stalled and always starts on the first try. At times there is a rotten egg odor and sometimes its quite noxious !. There are no stored or current codes (not since the O2 sensor last year)

    If I open the throttle plates when engine is off I hear a faint bubbling noise and the TB smells faintly of gas. Whe I rev the engine to around 3000 rpm and let go of the pedal it is sometimes followed by a small pop in the exhaust.

    So to make a long story short, I think I have an injector problem. I hope I gave enough info to go on !

    Thanks

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    Re: How to find the leaky injector

    You may be right.

    You cleaned the EGR tubes out that are beneath the throttle body blades in the intake manifold...???

    To check the injectors is very simple at this point. Loosen and remove the 4 fuel rail hold-down bolts and lift the fuel rail up slightly so that the injector tips clear the intake ports. You can block it up with some wood shims/blocks. Turn on the key/energize the fuel pump to presurize the fuel rail and watch the injector tips for leakage. Simple as that.

    Did you check the FPR by pulling the vacuum line off while the engine is idling?? Just pulling the vacuum line off may not show if there is leakage past the diaphragm as the fuel will get sucked away by the vacuum and thru the vac line and into the intake. Pull the vac line off while the engine is idling and plug it(the vac hose, not the nipple on the FPR). Let it idle for several minutes and watch the vac nipple on the FPR for any signs of fuel leakage.

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    Re: How to find the leaky injector

    You cleaned the EGR tubes out that are beneath the throttle body blades in the intake manifold...???

    yep, those and under the EGR valve itself.

    I'm going to try this weekend to pull the rail up. I guess it will just be really evident when I look if they are leaking. My fuel used reading also says that I used 14 gallons of gas when the gas pump says 16.5 gallons (just a point for others when they search for an answer)


    Thanks

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    Re: How to find the leaky injector

    Quote Originally Posted by up2ng
    yep, those and under the EGR valve itself.

    I'm going to try this weekend to pull the rail up. I guess it will just be really evident when I look if they are leaking. My fuel used reading also says that I used 14 gallons of gas when the gas pump says 16.5 gallons (just a point for others when they search for an answer)


    Thanks
    I meant to ask you if the electronic fuel used matched the actual fuel used....LOL.....from what you indicate the electronic fuel used is low...which would indicate some "unregulated" fuel is going thru the sytem. This would be a sign of a fuel pressure regulator leaking internally or an injector dripping or hanging open as has been mentioned. The electronic fuel used should always be very very close to the actual fuel used. The electronic fuel used is based on an accumulation of all the injector pulse widths that the PCM has issued to the injectors. If the injectors are delivering exactly what the PCM is commanding then the electronci fuel used calculation is perfectly accurate. If something is happening to let fuel past the injector that the PCM does not "know" about then it would make the actual fuel used higher than the calculated number.

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    Re: How to find the leaky injector - Follow up

    OK, the car finally got to the point of a full blown miss today, so I started pulling spark plug wires and what did I find ?

    I found that when I moved on of the wires a noise that I previously thought was a valve tap was really a wire hanging 1/4 inch above the crossover pipe ! The damn thing was arcing for quite some time because there is now a spot weld in the pipe where the wire was (at least the coil is strong !) and the wire has a 2 inch split in it and is hard as a rock.

    I'm going to change the plug since it has been seeing raw gas for awhile and change the wires (plus route them differently).

    I'm glad it wasn't the injectors because they are $95 a pop.


    Thanks for all the help though

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    Re: How to find the leaky injector - Follow up

    Quote Originally Posted by up2ng
    OK, the car finally got to the point of a full blown miss today, so I started pulling spark plug wires and what did I find ?

    I found that when I moved on of the wires a noise that I previously thought was a valve tap was really a wire hanging 1/4 inch above the crossover pipe ! The damn thing was arcing for quite some time because there is now a spot weld in the pipe where the wire was (at least the coil is strong !) and the wire has a 2 inch split in it and is hard as a rock.

    I'm going to change the plug since it has been seeing raw gas for awhile and change the wires (plus route them differently).

    I'm glad it wasn't the injectors because they are $95 a pop.


    Thanks for all the help though

    I thought you said that you had changed the spark plug wires earlier....????

    Glad you found it anyway.!!!

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    Re: How to find the leaky injector

    I was just reading this post and saw that the problems UP2NG was having with his car are similar to mine, I have a 93 deville, that has been acting up for some time. It first started with running rough and getting horrible gas mileage so I did a major tune up and it made a little bit of a difference but not much. So I brought it to Cadillac and they told me my thermostat was stuck open and I had a bad O2 sensor, so I changed them, and whammo, I started to get real good mileage again, but now a new problem started. Now the car would run smooth but at a pretty low idle, and sometimes has a real low acceleration hesitation, and after it has been running then shut down and started again the idle will fluctuate up and down, also the ISC ratchets after shutdown. So far I have changed the ISC motor, and the TPS and cleaned the throttle plates and EGR tubes and Throttle body. Everybody I have spoken to has said injectors, but I need a way to test them to get hard evidence of a failure, at 95 bucks I am not going to pop and swap when it might be a bad ECM, also I am getting no codes. This is driving me nuts, anybody got and ideas?

    Jack

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    Re: How to find the leaky injector

    I have the same problems as you Cadillacjack..I have done everything to my 91 eldo and nothing has fixed it.No codes and it runs like someone beat it with an ugly stick Not sure if changing the ecm would work,I suggested that a few times to cadillac and they said it wouldn't fix it but if it does let me know.

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    Re: How to find the leaky injector

    Not getting codes CaddyJack is my problem too but I found this..might help

    Some control module's may have problems due to cracked solder joints on the circuit board. These internal control module problems can cause the following symptoms:


    • Failure to start or vehicle is stalling.
    • The "CHECK ENGINE" "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR" light will flash or light up, but no trouble codes will be present.
    • Vehicle instrument panel displays may be inoperative.
    • The control module may or may not communicate with the scanner.
    • Other intermittent driveability problems.
    Incorrect PROM or MEMCAL removal and replacement can create solder joint problems or aggravate an existing condition. See PROM or MEMCAL INSTALLATION for proper procedures.

    If a solder joint problem results in a "hard" failure, normal test procedures will usually pinpoint a faulty control module. Many symptoms caused by poor solder joints in the control module result in intermittent problems, but they may be hard to duplicate during troubleshooting. Control module's with solder joint problems are sensitive to heat and vibration. You can check for these internal control module problems in either, or both, of the following ways:


    • Remove the control module from its mounting bracket and extend it on the harness so that you can expose it to the vehicle heater ducts. Alternatively, use flexible ducting to route air from the heater to the control module location. Then run the engine and operate the heater at the "MAX HEAT" position. This exposes the control module to approximately 140°F.
    • With the engine running, tap on the control module several times with your hand or finger tips to simulate vehicle vibration.
    If the engine stumbles or stalls, the "CHECK ENGINE" "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR" light flashes, or any of the previous symptoms occur, the control module may have bad solder joints on the circuit board.

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