Reckless32

Out of the blue last weekend both my 496's will fire up and run for a few minutes then, begin sputtering and choke out and idle one after the other. I lost an impeller on one as well that day.

This year I've installed new boost pumps, hear normal pressurizing of the main pump for 3 seconds when you turn the key on. Mechanical fuel gage reads roughly 38-40 psi (should read 40-43 I think?) for awhile on each, then begins to drop during the subsequent sputter. Both motors on the same day are doing this which makes me think there's a common denominator causing this and the only thing that comes to mind is the fuel tank or check/anti-syphon valves or whatever they're called. Perhaps even the fuel vent?

Any thoughts or suggestions on where to start with the simple stuff and work my way up to the difficult?

-motors are 2004 with separate fuel pumps (boost/main opposite sides of motor)
-New seperators changed very frequently each yeasr since using ethanol
-new boost pumps each motor
-cleaned out injectors of a gritty material, no codes
-new IAC's spring of 2007
-have my own Rinda scan tool and they have no fault codes

MOBILEMERCMAN

You said new boost pumps. Did you just open the fuel system? The gauge won't know if it is air or fuel pressure. If system has been open fill the filters with fuel.

It is easy to use a remote {outboard } can hooked directly to motor to see if its in the boat or the motor.

Reckless32

Didn't have to remove the filters. Just two nuts holding the bracket containing the filter and boost pump bracket. Filters were replaced probably 2.5 hours of running ago prior to now. When I do replace filters I always fill or at least make it half to 3/4 with fresh fuel and prime the pump with key turns 3-5 times the first time started.

Again the anomaly is that it happened to both on the same day which is why I'm thinking its got to be something of a common denominator for both engines to cause fuel pressure drop. No leaks and once pressurized the gage will hold the pressure indefinitely until started and let run for awhile, then they will trail off.

I had an impeller go out last Saturday and back flushed the mostly complete impeller parts out accounting for all. But the raw water pumps on each motor appeared pretty scored up at each end cap (if i pull one to change an impeller, I pull both).

So another theory/thought may be since it (pressure) doesn't happen drop off right away, and if let set for awhile will fire up and run normally for a few minutes to include racing the rpm a time or two before they lose pressure, may be both pumps are just worn and not creating enough cooling effect which in turn is causing a vapor-lock??? But still there's that coincidence of happening at the same time which is why maybe the tank aspect comes to bare?

Again no codes on the Rinda scan tool.

thedonz

try replacing the check valve, I had similar symptoms on one of my motors and it was the check valve

good luck

Reckless32

Check valve is right there where the line enters the fuel tank right by the 90 degree brass elbow, correct?

I'm replacing both sea water pumps today and will give both motors a good back flushing while the pumps are off just for GP. I will also be inspecting the check valves and fuel tank vent as well....Trial and error, or process of elimination right?...

hp500efi

pull both fuel pumps and check for debris. I had LOTS of debris on the inlets to my pumps. New pumps or not, debris from the tank is inevidible.

Reckless32

Inspected for check valves yesterday amongst other things, and no check valves installed. Clean clear hose/tubing. I'm gonna swap around my boost pumps (one side wants to run longer than the other) just to see if the extra run time follows and i will peek at the inlet screens. My biggest fear is it will be the mina pumps or the cool-fuel system gone bad. Those would require a motor pull. Damn a bunch of people heading tot he eastern shore tiki and as of right now I'm land-locked....