Low Pressure Fuel Pump Relay Not Receiving 'Switched' Power

[tachyon]

I have some specific questions on my low pressure & high pressure fuel pumps for my GT40 - the boat is currently not running;

1. Do the high pressure and low pressure pumps run simultaneously (i.e. is Terminal 30 essentially 'common' to both of the pumps)?
2. If I need the boat to run Friday...until next Sunday... for our 'big' summer vacation, can I simply wire Terminal 30 from the HP pump to the LP pump so they both will run simultaneously?
3. What conditions need to be met for the low pressure pump to run? Are these conditions the same as the high pressure pump?


The boat is a 2001 Super Air Nautique with GT40 engine (and perfect pass...in case that makes a difference!). I've scoured the forums for help, and have finally narrowed down the failure to terminal 86 on the relay plug for the low pressure pump. Turns out that it is not cycling to +12V when hit start on the keypad - or if I crank the engine with the keypad. Why?

I have tested both HP and LP fuel pumps, both relays, and finally got out the multi-meter to see what is happening. Terminal 86 on the low pressure pump relay plug is getting -30mV when I crank the engine and with no relay plugged in. For the high pressure relay plug, I get about 12V at Terminal 86 when cranking.

I should note that the boat was running OK on the last 3 outings. I recently re-carpeted & surely pushed the wiring harness around a bit under the dash, etc... is there a wire down there that I should trace?

I have hard-wired to the low pressure pump from terminal 30 - and the pump runs perfect. I've also done the obvious relay-swapping, etc... with no luck.
Please help - thanks in advance! [:^(]

[DanielC]

You can download the GT-40 service manual from the downloads section of this site. Do it now.
Near the back of that manual, are simplified wiring diagrams for various engine electrical systems.

Both fuel pumps receive power from pin 87 of the fuel pump relay. Pin 30 on that relay is always hot. The fuel pumps are wired in parallel.
The coil of the fuel pump relay (pin 85) receives power from pin 87 of the EEC system relay. Pin 30 of that relay is also always hot.
When the engines computer decides the fuel pumps need to be on, it grounds the coil (pin 86) of the fuel pump relay.

The fuel pumps should not be connected to pin 30 of the relay.

Here is my thread on checking the fuel pump pressure on a GT-40 engine.
http://www.planetnautique.com/vb3/sh...=fuel+pressure
Here is some information about relay connections.
http://www.planetnautique.com/vb3/sh...=fuel+pressure

The first thing to check when the fuel pomps do not cycle on when the key is turned on is the safety lanyard. The engine shut off on a GT-40 interrupts the power to the fuel pumps. No fuel pressure, no run.

Again, there is only one fuel pump relay, and it controls both fuel pumps at the same time.

If you look at the second picture in the fuel pressure thread, you will see a jumper wire, with a fuse in it, connecting the lower right terminal of the test port to ground. This commands the computer to turn the fuel pumps on. The key needs to be on for this test

[Mrbigbirdmk]

The pump probably just needs to be replaced. Contact you local Nautique dealer about a new pump. They are easy and quick to replace.

[Mrbigbirdmk]

The pump probably just needs to be replaced. Contact you local Nautique dealer about a new pump. They are easy and quick to replace.

I forgot to say the low pressure pump on the outside of the canister.