Gt40 intermittent hot start

[75animal]

99 snob with gt 40 550 hours won't start when hot. Narrowed it down to no power to fuel pumps . Changed relays but no result. Been chasing this for a while now but realised that when pumps run the engine will. Cold start no problem, only when hot after shutdown. Motor runs fine otherwise, have checked fuel supply/ filters and all is good. I have checked pumps with other power source and all is good. Thinking maybe ecu or earths, any help/ experience with same would be greatly appreciated!

[AirTool]

Have you checked for spark during this condition?....using and inductive timing light or inductive pen doodad?

I have a theory.

[75animal]

I have spark. Just pulled a plug and checked back to the block. Was spark every time. The fuel pumps not turning on is my only breakthrough. Willing to hear the theory though.

[DanielC]

Down load the GT-40 service manual form this site, down loads section.
The manual does have good wiring diagrams in the back.

The two cube relays always have battery power on pin 30. The fuel pump relay coil gets power from the contacts in the ECC relay. The fuel pump relay coil is grounded by the engines computer. The fuel pumps are grounded. When the computer wants the fuel pumps to run, it simply grounds the fuel pump relay coil.

A quick and dirty test, connect pin 30 and pin 87 on the fuel pump relay socket. This will cause the fuel pumps to run, even with the key off.
This thread is about checking the fuel pressure, but the part about using the test connection to tell the computer to turn on the fuel pump may be helpful to you.
http://www.planetnautique.com/vb3/sh...=fuel+pressure

In case you are not familiar with the relay connections, this thread will help you.
http://www.planetnautique.com/vb3/sh...=fuel+pressure

[slob02]

Does your boat have the fuse at the battery? Check for corrosion if it does. I also believe the lanyard shuts off the fuel pumps when pulled. Another cheap place to check. Not sure about the heat relationship?

[75animal]

No fuses, and just redid the battery connections. Going to go over relays again as cover those bases. Checked lanyard and boat still starts but won't keep running once forward is selected. I'll get there, but just frustrating as this is my only problem. When the boat is going it is unstoppable. Once off will not start . Thanks for the input.

[AirTool]

I have spark. Just pulled a plug and checked back to the block. Was spark every time. The fuel pumps not turning on is my only breakthrough. Willing to hear the theory though.

The theory (common cause) for "no spark when hot" is the ignition control module's "low speed" circuit is bad when hot. Often they are good cold....the engine starts and (after 400 ish) RPM the "fast speed" circuit takes over. Then when the engine is shut off and the "low speed" circuit is needed for starting...no go.

[75animal]

Still have spark.

[75animal]

Sorry, just read who posted. My apologies

[AirTool]

Sorry, just read who posted. My apologies

de nada.

[slob02]

When you say "relays", did you change out both of them at the same time? This has to be driving you crazy!!!

[75animal]

New info to add to the problem. When the motor doesn't want to start I have discovered that pressing the horn then turning the key the motor starts again. No this is not a joke. Came over it by accident, but works every time. The ignition also beeps again so I figure that the ignition is being reset by a spike? At least I am not waiting for the boat to start. I am thinking earth wiring somewhere in the labrinth of wiring is not quite right. I am also questioning the perfect pass. Does anyone have any ideas?

[Rick]

Corrosion on the Earth circuit. Check the wire at the motor and at the dash. I may also be a bad cell on the battery. I would have them do a stress test on the battery. Whe you honk the horn and turn the key at the same time does the tone or volume of the horn go down?

[75animal]

Thanks mate I will check that out and do the test. The volts do change when you press the horn

[75animal]

I have sorted the problem finally!Poor connection on the back of the ignition barrel. Cost- 0. Thanks to all who offered help.