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1999 SN GT40 Will Not Run at rpm > 1,000

ab38off

New member
Went skiing the other day and after 4 runs down the lake, the engine gasped and died when accelerating. We were able to limp back to the dock at idle, but any time giving the slightest bit of throttle, the engine would gasp and die.

Background:
About 400 hours on the boat.
Last year replaced the low pressure pump, kill switch, filter, and anti-siphon valve. Eventually found the fuel relay to be the problem.
The boat was just randomly cutting out like a kill switch issue. Later learned that the relay goes out gradually and acts like this a lot of times.

Current:
While replacing the filter after the problem described above, (everyone thought is sounded like a plugged filter) the wire seal on top of the FCC leaked, so I now have a new FCC (it is sold as a complete unit with high pressure pump) and it is still doing the same in the driveway. I was able to test the fuel rail pressure and observe that it was up around 40 and as I gave it some rpms, the pressure dropped to 0, then was just surging at idle, like it is getting shots of gas, but didn't idle smooth after it gasped at rpm. I say gasped, because that is the sound I am hearing from the engine.

My thought is the year-old low pressure pump is bad or the fuel relay is acting up again. This is different than the problem I had last year, when the boat would run fine, then just die.

Any thoughts or prior experience with something like this?

Thank you.
AB
 
Can you verify that the low pressure pump is working while the engine is running? You can, for test purposes only, install an outboard squeeze bulb in the fuel feed line and pump it while running the engine to see if your Fuel pressure stays up on the rail.

Next, assuming you have a vacuum operated fuel pressure regulator, start the engine and disconnect the vacuum line and plug it while checking the fuel pressure.
 
The other thing I wanted to mention was that when I normally turn the ignition on, I can hear the pumps prime. After the engine stopped, the pumps didn't respond to turning on the ignition. That is why I am suspecting the relay again.

I don't have access to a bulb, but that is a good idea. I guess I could drain the FCC and see if it is full after a failure. Doesn't the low pressure pump fill the FCC?
 
I ordered both relays today. I am being told I should have replaced both at the same time. I only replaced the fuel relay last year.
I guess I might have a spare if one is only bad.

Any way to test these to see if they are bad?
 
I put both relays on today (a little late due to knee surgery) and I am not hearing pumps priming. I put a new low pressure pump on last year, so only about 50 hours on it.

What else causes the pumps NOT to prime or lose pressure when the engine is running??
 
A blockage or a leak on the suction side will cause the pumps not to prime. while you are doing all of this testing, what is the fuel level in your tank? I would pull the dip tube from the tank and make sure that it is not cracked or broken. Some boats have plastic dip tubes and are prone to cracking.
 
The motors are not running when you turn the key to on. I believe that I should hear the motors run before the starter motor is engaged. I am pretty sure this is how it was when I replaced the relay last year. There is plenty of gas in the tank and the anti-siphon valve is not plugged, I checked those early on.

Seems like an electrical thing now. Maybe the low pressure pump has gone bad. Should both pumps prime, or make noise when key is turned on? I could even feel the low pressure pump vibrate before. Now I am not getting anything. I am not sure if the pump in the FCC primes. I would assume so...

Last year, the relay was intermittantly cutting out before it eventually just failed competely. I replaced the kill switch and pump, and then found it to be the relay.

This does not give off error codes, and any repair shop would have to manually go through it. I learned that last year too.
 
Carbs, Carbs, Carbs...Clean and check your floats, not to mention your fuel supply. Compression good and stalls results to poor or clogged fuel. Go with your gut on extra expenses, Corrosion Spray will help in the long run and tighten any loose connections.
Thanks and Merry XMas












Went skiing the other day and after 4 runs down the lake, the engine gasped and died when accelerating. We were able to limp back to the dock at idle, but any time giving the slightest bit of throttle, the engine would gasp and die.

Background:
About 400 hours on the boat.
Last year replaced the low pressure pump, kill switch, filter, and anti-siphon valve. Eventually found the fuel relay to be the problem.
The boat was just randomly cutting out like a kill switch issue. Later learned that the relay goes out gradually and acts like this a lot of times.

Current:
While replacing the filter after the problem described above, (everyone thought is sounded like a plugged filter) the wire seal on top of the FCC leaked, so I now have a new FCC (it is sold as a complete unit with high pressure pump) and it is still doing the same in the driveway. I was able to test the fuel rail pressure and observe that it was up around 40 and as I gave it some rpms, the pressure dropped to 0, then was just surging at idle, like it is getting shots of gas, but didn't idle smooth after it gasped at rpm. I say gasped, because that is the sound I am hearing from the engine.

My thought is the year-old low pressure pump is bad or the fuel relay is acting up again. This is different than the problem I had last year, when the boat would run fine, then just die.

Any thoughts or prior experience with something like this?

Thank you.
AB
 
I have traced it back to the fuses on the back of the motor.
Tapped on them with the butt end of a screwdriver (can't push them in) and the fuel pumps primed.

I now can see there is a leak on top of the FCC, so need to fix that as well.

Im getting new 15 and 12.5 amp breakers and will hope that takes care of the pump issue.
Will re tape and tighten the fittings to see what or why it is leaking gas.

I may have forgottten to put pipe tape on the threads.

Getting closer I hope.
 
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