95 SN GT40 - Running rough till warm???

[Adam B]

First - I haven't been skiing yet which is killing me!!! In Ontario we only get a short window and my boat problem is eating into that time. Please help

Quick background - 95 SN with a GT40 and about 1100 hours. Has ran great for me for many years - until now.

Season opener - boat ran on trailer before putting in - not an issue.
Dropped it in and it didn't start - low pressure fuel pump not priming (relays checked, kill switch bypassed etc) ... but it kicked in briefly on a couple tries.

After trying to diagnose I finally brought it to the marina - they couldn't figure it out so they somehow bypassed a line to get the fuel pump to prime
(quick note here... before the pump would prime and shut off.... now the fuel pump primes and keep on running). (also note - that while they had it in the shop they changed plug, cap, rotor and belts)

NOW.... get the boat back and dropping it in. Had to push it to full throttle to keep it running and the engine cough and spit and blew black smoke... back off the throttle and it wont idle....brought the boat back...

So the mechanic has tried it daily. Said the first 5-10 min the boat does this cough and spit daily. After that it settles in and starts to purr fine when warm. Warms starts after that are fine too. They've water tested it etc.

What could it be??? Sensor somewhere? The fact that the fuel pump doesn't prime then stop? Mechanic and myself are asking for help!

Thanks guys.

[Peter6000]

First - I haven't been skiing yet which is killing me!!! In Ontario we only get a short window and my boat problem is eating into that time. Please help

Quick background - 95 SN with a GT40 and about 1100 hours. Has ran great for me for many years - until now.

Season opener - boat ran on trailer before putting in - not an issue.
Dropped it in and it didn't start - low pressure fuel pump not priming (relays checked, kill switch bypassed etc) ... but it kicked in briefly on a couple tries.

After trying to diagnose I finally brought it to the marina - they couldn't figure it out so they somehow bypassed a line to get the fuel pump to prime
(quick note here... before the pump would prime and shut off.... now the fuel pump primes and keep on running). (also note - that while they had it in the shop they changed plug, cap, rotor and belts)

NOW.... get the boat back and dropping it in. Had to push it to full throttle to keep it running and the engine cough and spit and blew black smoke... back off the throttle and it wont idle....brought the boat back...

So the mechanic has tried it daily. Said the first 5-10 min the boat does this cough and spit daily. After that it settles in and starts to purr fine when warm. Warms starts after that are fine too. They've water tested it etc.

What could it be??? Sensor somewhere? The fact that the fuel pump doesn't prime then stop? Mechanic and myself are asking for help!

Thanks guys.

The pump has a relay the relay has plus on one coil side the other side is connected to ecu when ignition is turned on the ecu pulls to ground for 2 sec the relay switches and both pumps turn on for 2 sec or so.
After start both pums are turned on by the ecu.
Details are in the pro boss manual available under manuals on this site.
Black smoke points to running rich, does it smell like gas too?
I would start with measuring fuel pressure on the rail.
Make sure pressure stays up after turning ignition off above 30psi for at least 10 min.
If not you have a leaking fuel injector.
Check the spark plugs are the wet?
Check ignition power on all plugs and timing.
If still no luck check all sensors there are only a few.
Peter


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