"I have a 2001 5.7 GXI-A with
"I have a 2001 5.7 GXI-A with TBI and the other day I was about 28 miles offshore cruising at about 3800 RPM when I suddenly lost power.. I brought it back to idle quickly, and everything seemed normal, so I proceeded to resume running out to the fishing spot. I got up to about 3500 RPM for a minute or so when the engine started "surging", fluctuating about 500-800 RPM every few seconds and slowly decaying to idle where it ran fine...
figured I ran into a patch of bad gas or some water saturated the filter so I pulled it and drained into clear container, everything looked fairly normal, no debris and very little water.. but I changed out the filter anyway as I carry spares..
anyway I fought it all the way home, it eventually got to the point where it would die instead of return to idle, but it would immediately crank back up and run fine until I tried to throttle up.. it was very incosistent though because at time I was able to hold 2800-3500 RPM for 5 minutes at a time before it resumed surging..
at this point I have checked all obvious things I can think of as far as loose wires or fittings, hoses, breakers, overheat limit, and all my gauge readings are normal..
back at the dock, I hooked a fuel pressure tester to the high and low test ports and they read normal: 30PSI on the high and just under 10PSI on the low at normal operating temp.. so I ran the boat with the pressure tester hooked up on the high side and when the surging occurs the pressure dropped to 5PSI! sooo I swapped the high pressure fuel pump, but it didn't change a thing! the only other thing I noticed is that immediately after the surging the whine or squeal from the fuel pumps is noticably higher than normal... and I disconnected the low pressure pump as a "drop cylinder" type test and that makes it sound the same...
my logic now is this: the low pressure pump sucks from the tank into the fuel cell, and the high pressure pump sucks from the fuel cell and sends to the injectors.. now, the boat will run with the low pressure disconnected, it just seems that the high pressure pump pulls double duty and can't keep up at high RPM..
I figure if the low pressure pump is damaged or not operating right, then this could be causing my problem as the engine would run fine at idle with the high pressure pump hiding the problem when there is very little demand.. and the the accumulated pressure in the fuel cell can supply the volume for a few minutes or so, but it is a loosing battle of course and causes the surging when it runs out and the high pump cant supply the volume of fuel needed consistently from the tank alone, and then when I go to idle or restart, the pump has a chance to catch up a bit until I try again...
is there an off chance that there is another type of screen or debris filter that I'm missing maybe in the fuel tank that could be casuing this problem??
I'm hoping someone who knows a little more about the system can check my logic or point me in a new direction.. I'm fairly confident it's the fuel system and my ignition system has all conponents recently replaced and proven running well and I've run through the sensors linked to the throttle body pretty well.. any help would be greatly apprecriated! I didn't mind spending the $200 on a high pressure pump to no avail because it was about time to think about replacing or carrying a replacement anyway.. but before I drop another $400-$600 on the rest of the assembly I'd like a second opinion! thanks again!
additional info: it runs fine throughout the RPM range in neutral (NOT under load) logic check: I'm assuming this is because the demand for fuel is much less than when pushing the boat through the water..?"
"I have a 2001 5.7 GXI-A with TBI and the other day I was about 28 miles offshore cruising at about 3800 RPM when I suddenly lost power.. I brought it back to idle quickly, and everything seemed normal, so I proceeded to resume running out to the fishing spot. I got up to about 3500 RPM for a minute or so when the engine started "surging", fluctuating about 500-800 RPM every few seconds and slowly decaying to idle where it ran fine...
figured I ran into a patch of bad gas or some water saturated the filter so I pulled it and drained into clear container, everything looked fairly normal, no debris and very little water.. but I changed out the filter anyway as I carry spares..
anyway I fought it all the way home, it eventually got to the point where it would die instead of return to idle, but it would immediately crank back up and run fine until I tried to throttle up.. it was very incosistent though because at time I was able to hold 2800-3500 RPM for 5 minutes at a time before it resumed surging..
at this point I have checked all obvious things I can think of as far as loose wires or fittings, hoses, breakers, overheat limit, and all my gauge readings are normal..
back at the dock, I hooked a fuel pressure tester to the high and low test ports and they read normal: 30PSI on the high and just under 10PSI on the low at normal operating temp.. so I ran the boat with the pressure tester hooked up on the high side and when the surging occurs the pressure dropped to 5PSI! sooo I swapped the high pressure fuel pump, but it didn't change a thing! the only other thing I noticed is that immediately after the surging the whine or squeal from the fuel pumps is noticably higher than normal... and I disconnected the low pressure pump as a "drop cylinder" type test and that makes it sound the same...
my logic now is this: the low pressure pump sucks from the tank into the fuel cell, and the high pressure pump sucks from the fuel cell and sends to the injectors.. now, the boat will run with the low pressure disconnected, it just seems that the high pressure pump pulls double duty and can't keep up at high RPM..
I figure if the low pressure pump is damaged or not operating right, then this could be causing my problem as the engine would run fine at idle with the high pressure pump hiding the problem when there is very little demand.. and the the accumulated pressure in the fuel cell can supply the volume for a few minutes or so, but it is a loosing battle of course and causes the surging when it runs out and the high pump cant supply the volume of fuel needed consistently from the tank alone, and then when I go to idle or restart, the pump has a chance to catch up a bit until I try again...
is there an off chance that there is another type of screen or debris filter that I'm missing maybe in the fuel tank that could be casuing this problem??
I'm hoping someone who knows a little more about the system can check my logic or point me in a new direction.. I'm fairly confident it's the fuel system and my ignition system has all conponents recently replaced and proven running well and I've run through the sensors linked to the throttle body pretty well.. any help would be greatly apprecriated! I didn't mind spending the $200 on a high pressure pump to no avail because it was about time to think about replacing or carrying a replacement anyway.. but before I drop another $400-$600 on the rest of the assembly I'd like a second opinion! thanks again!
additional info: it runs fine throughout the RPM range in neutral (NOT under load) logic check: I'm assuming this is because the demand for fuel is much less than when pushing the boat through the water..?"