2004 Launch fuel pressure drops down to 30 psi under load

[jjgag60]

We have a 2004 Launch with the indmar 5.7. Installed a fuel pressure gauge on it and it runs smooth under no load. When i put it in neutral and accelerate quickly gaugestays at 60 psi. Under load, at heavy acceleration the motor bogs down at about 2500 rpm or about 30 seconds into the full throttle, the fuel pressure drops between 20 and 30 psi, and then comes back up to 60 psi and the motor catches up and accelerates okay. Replaced the fuel pump, checked ball valve and installed a new filter, I can't find the old one and some one said
there isn't one on some Supra's. Problem is still there, at heavy acceleration under load, fuel pressure drops and now i hear a little bit of a back fire or popping noise. Any ideas?

[jjgag60]

Update: We changed out the fuel regulator to see if that would solve the problem after talking to Indmar. The same problem still exist. From a dead start in the water, fuel pressure is 60 psi, accelerate hard and at about 2,000 rpm, the fuel pressure drops to about 20 psi, for about 10 seconds, motor bogs down, and then the pressure starts up to 30 and then jumps to 60 psi and off we go. Motor then runs fine.

[docdrs]

Maybe you need to check the pressure just after the pump to see if it drops there. I assume your checking it on the rail. I would check the voltage and amps to the fuel pump. .02

[jjgag60]

sounds like an idea, but how would you do that? The outlet on the pump runs into a brass fitting and then into a steel tubing. I am thinking about trying to figure out a way to check it prior to the pump and see if there is a difference between idle and then hard acceleration. That might tell me if there is a kink or a hidden filter that is causing loss of pressure on accelertaion.

[jjgag60]

Okay i found a mechanic who works on Supra's and he said there is a fuel filter on the 04 Launch direct drive mounted to the stern behind the fuel tank, behind the
carpeted panel. I pulled the carpeted panel and he was correct, there is a fuel filter mounted there between the air duct hoses. I have a WIX filter on order and
tomorrow we will see if it fixes the problem. My fingers are crossed.

[jjgag60]

So today I replaced the fuel filter and found it was put in backwards. After replacing the filter the boat runs fine. The moral of the story is, the fuel pressure gauge is your best friend when trying to figure out problems with your boat. Sitting at the dock, the gauge didn't indicate any problems, it was under load that the pressure dropped to 20 psi from 60 psi. Electrical problems don't cause pressure to suddenly drop and then shoot back up. A blocked fuel line, fuel pump or regulator all can effect the pressure. It was an expensive fix, pump, fuel regulator and then come to find out it was a 15.00 filter, the good news is I now know a lot more about the boat and how the fuel system works. I think i still saved over sending it to the shop and having to spend $90. an hour to have them trouble shoot the problem and wait the two weeks to get it in. My guess they can't put the motor under a load in the shop and test the fuel pressure reading. Having the gauge attached to the motor and running
it in the water helped solve the problem.

[CornRickey]

And you have a spair fuel pump and regulator