496HO need help, serious problem
12-14-2006, 05:26 PM
#41
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Re: 496HO need help, serious problem
I had the same problem 2 years ago. The inlet screen was clogged. Mine eventually plugged the injector screens. The filter Dixie Doug mentioned is what prevented further problems.
12-24-2006, 11:50 AM
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Re: 496HO need help, serious problem
Originally Posted by stevesxm
would refer you to the thread that i ran some weeks back where went thru exact same thing... and did all the same stuff.
run perfect one minute, flat on its face the next. in my case it was one bad injector...bad as in shorted internally. you might want to look at that thread as an idea of what was done in what sequence... went thru the whole fuel presure thing because acted just like you say but bottom line was that motors run fine with a whole range of fuel pressures... and by fine i mean that the differences you observe are not enough to make the motor run " badly" not perfect fuel curve for sure but would run cleanly on 8. in my case it became apparent that as the injection pulses 4 injectors at a time that the shorted one was electrically affecting the pulse width of the other 3 on the same circuit.... enough to make the motor run just like you say ... except when it didn't.
the merc tool has an injector pulse function. i took the injectors out, pressurized them and pulsed them and found the bad one... replaced it and the motor has been perfect since....
am simply saying that symptom from THIS failure had me checking and testing EVERYTHING else .... just like you are...
run perfect one minute, flat on its face the next. in my case it was one bad injector...bad as in shorted internally. you might want to look at that thread as an idea of what was done in what sequence... went thru the whole fuel presure thing because acted just like you say but bottom line was that motors run fine with a whole range of fuel pressures... and by fine i mean that the differences you observe are not enough to make the motor run " badly" not perfect fuel curve for sure but would run cleanly on 8. in my case it became apparent that as the injection pulses 4 injectors at a time that the shorted one was electrically affecting the pulse width of the other 3 on the same circuit.... enough to make the motor run just like you say ... except when it didn't.
the merc tool has an injector pulse function. i took the injectors out, pressurized them and pulsed them and found the bad one... replaced it and the motor has been perfect since....
am simply saying that symptom from THIS failure had me checking and testing EVERYTHING else .... just like you are...
12-24-2006, 12:35 PM
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Re: 496HO need help, serious problem
Just a question. I thought that the inline fuel filter between the gas tank and the first fuel pump was there to collect the gas tank garbage. How is it that this stuff is getting past this inline filter and collecting on the first fuel pump inlet screen?
12-24-2006, 12:44 PM
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Re: 496HO need help, serious problem
Fuel pressure is checked by installing a pressure gage on the fuel rail, and turning on the ignition but not starting the engine. You will hear the fuel pump pressurizing the system. The max fuel pressure reading that you get before the fuel pump stops running is the set pressure and should be 43 psi for the 496HO. When the pump stops the pressure drops off to a lesser value. When running the 496HO at WOT it should be able to maintain the 43 psi at the fuel rail if everything is working properly. You will likely get some pressure gage needle flutter from the injector pulse feed back into the fuel line but the nominal should be close.
12-26-2006, 04:01 PM
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Re: 496HO need help, serious problem
Originally Posted by Rage
How exactly did you pressurize and test the individual injectors? Did you remove the fuel rail with injectors attached and individually test fire them (into a jar or something to catch the fuel) that way?
12-27-2006, 10:53 AM
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Re: 496HO need help, serious problem
Originally Posted by stevesxm
ill find it and get you a thread # .... all you have to do is get the injectors out in your hand... on my motors that was less than 20 mins.... then i just ose clamped the high pressure line to it and cycled the pump a few times to buld pressure and then used the scan tool injector test circuit to pulse them... once out takes about 5 mins per injector.
let me tell you.... i checked EVERYTHING... spent 3 full days or more on every concieveable thing... fortunately mine is a twin engine boat so i had another of " everything" to swap out so i could confirm good or pad parts...
amazing thing was that motor did not go on a clean 7 with the bad injector... ran SO bad and flat...just like yours that i convinced myself it was elsewhere and systemic... not cylinder specific... but thats exactly what it was.
let me tell you.... i checked EVERYTHING... spent 3 full days or more on every concieveable thing... fortunately mine is a twin engine boat so i had another of " everything" to swap out so i could confirm good or pad parts...
amazing thing was that motor did not go on a clean 7 with the bad injector... ran SO bad and flat...just like yours that i convinced myself it was elsewhere and systemic... not cylinder specific... but thats exactly what it was.
02-16-2007, 08:01 AM
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The fuel pressure across the tip of the fuel injector (fuel pressure delta) is what the fuel pressure regulator is trying to regulate, and this pressure (approx 40 psi for 8.1L) should remain "relatively" constant if the engine is at steady state. So... The fuel pressure should be lower at idle that at WOT and slightly higher yet (usually) when the engine is not running and the ignition is keyed up for the pump to prime.
If you install a scan tool or vacuum gauge, and look at the manifold vacuum, you can verify the pressure regulator by adding the "negative" pressure in the manifold from the fuel pressure reading, and comparing this to the reading with the key on, engine off. The same holds true for a supercharged engine. If the manifold has 12 PSI boost, the regulator should add 12 PSI to the key on engine off pressure so the flow across the injector is the same. If the DELTA pressure drops more than 1-2 psi across the engine operating range (or when you experience your problem) there is likely a problem in the fuel delivery system somewhere. pump, regulator, filter, anti-siphon... If the reading varies < 2 PSI the problem is likely elsewhere.
If you install a scan tool or vacuum gauge, and look at the manifold vacuum, you can verify the pressure regulator by adding the "negative" pressure in the manifold from the fuel pressure reading, and comparing this to the reading with the key on, engine off. The same holds true for a supercharged engine. If the manifold has 12 PSI boost, the regulator should add 12 PSI to the key on engine off pressure so the flow across the injector is the same. If the DELTA pressure drops more than 1-2 psi across the engine operating range (or when you experience your problem) there is likely a problem in the fuel delivery system somewhere. pump, regulator, filter, anti-siphon... If the reading varies < 2 PSI the problem is likely elsewhere.
02-26-2007, 09:32 AM
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ill find it and get you a thread # .... all you have to do is get the injectors out in your hand... on my motors that was less than 20 mins.... then i just ose clamped the high pressure line to it and cycled the pump a few times to buld pressure and then used the scan tool injector test circuit to pulse them... once out takes about 5 mins per injector.
let me tell you.... i checked EVERYTHING... spent 3 full days or more on every concieveable thing... fortunately mine is a twin engine boat so i had another of " everything" to swap out so i could confirm good or pad parts...
amazing thing was that motor did not go on a clean 7 with the bad injector... ran SO bad and flat...just like yours that i convinced myself it was elsewhere and systemic... not cylinder specific... but thats exactly what it was.
let me tell you.... i checked EVERYTHING... spent 3 full days or more on every concieveable thing... fortunately mine is a twin engine boat so i had another of " everything" to swap out so i could confirm good or pad parts...
amazing thing was that motor did not go on a clean 7 with the bad injector... ran SO bad and flat...just like yours that i convinced myself it was elsewhere and systemic... not cylinder specific... but thats exactly what it was.
I am looking to repeat your injector cleaning procedure re: "then i just hose clamped the high pressure line to it (the injector)" The fuel line end fitting that connects to the fuel rail assembly is ~3/4" in diameter and the injectors ~ 1/2" in diameter. I could not find 3/4" fuel resistant rubber hose, only "heater hose" of that size. Could you describe the specific plumbing you used to connect the fuel line to the injector?
