Booster pump troubleshooting....2005...90HP Optimax

[DennisJJ]

Hi...I have a 90 HP..2005...Merc Optimax...S/N 1B055236...Model EXLPTO....Direct Fuel Injection...VST . I'm having a bit of grief with the fuel system. My low pressure and booster pumps have been checked and the PRESSURE part is all OK. As part of my trouble shooting, I want to check the VOLUME of fuel that is pushed through the BOOSTER PUMP, especially in the higher RPM range,....well, anything over 3000 (which is where the motor completely shuts down), but can't seem to find that number.....can anybody offer some advice ???....and just how would I go about measuring it.??

....as usual, thanks in advance for your assistance.

 

[CharlieB]

Re: Booster pump troubleshooting....2005...90HP Optimax

Flow testing injectors is a job for the injector shops.

I don't think that's exactly what you have in mind yet.

The fuel pump has to flow enough fuel to maintain PRESSURE at any given motor speed. If fuel pressure begins to drop at WOT then there is definitely a problem with the pump.

The problem is determining if you have a fuel, air compressor, or ignition system failing, so your troubleshooting can start narrowing down the culprit.

You need to rig the pressure gauges to check both fuel pressure and air pressure, and see what the pressures are while running at speed.

A timing light or inductive tach can be used to keep track of ignition, test each spark plug wire and see if any fail just as the motor starts to die.

Either pressure falls or you lose spark and the motor dies, you need to watch, test, to see which system is causing the problem.

Do you have a FACTORY service manual, it is great to see exactly how to test each system.

Check this link

http://forums.iboats.com/showthread.php?t=309079&p=2072211#post2072211

 

[CharlieB]

Re: Booster pump troubleshooting....2005...90HP Optimax

Air Compressor Pressure Test
Install Pressure Gauge Assembly 91-852087A1/A2 to fuel rail pressure test valves. The
fuel pressure and air pressure test valves are located on the starboard rail.
NOTE: After 15 seconds of cranking engine with starter motor, air pressure gauge should
indicate 79 ? 2 psi (544.0 ? 13.8 kPa) and fuel pressure gauge should indicate 89 ? 2 psi
(613.5 ? 13.8 kPa).

 

[DennisJJ]

Re: Booster pump troubleshooting....2005...90HP Optimax

Thanks very much for the information Charlie. It sounds waaaaaay to technical for me, but I'll pass the email along to the Authorized Mercury Dealer/Repair tech in the area and see if he can follow your leads and conduct those tests for me.