'03 Launch SSV Spitting/coughing after 1 hour

Hi all,

I have an issue that started after being on the lake for several hours.

Boat: 2003 Supra Launch SSV 350 TBI (5.7L Vortec)

It consistently follows the same pattern:

1) Go on lake for around 1 hour, everything runs great, can go WOT without problems even with a wakeboarder.
2) After 1 hour (hot engine), engine will pop/spit after pulling a wakeboarder or going under some type of load. When it begins spitting, it will continue to do so every few seconds until the boat is throttled back to idle.
3) If we try to go again, it only takes 2 minutes to start acting up again. Once it is acting up, don't need to pull anyone to start having problems. Any speed over 8 mph will do it.
4) If we wait for 20 minutes with the engine off, it seems to reset/cool down or and take 10 minutes to start acting up again (not confirmed).
5) Will occur at any speed over 8 mph once it starts. Has never occurred under this speed.

Have performed the following steps and diagnosis.

- New distributor cap and rotor
- New spark plugs and wires
- Have now been through 3 new half tanks of fuel. (Note: It started the 2nd weekend since being in the garage during winter. The first was a 2 day camping trip with no problems and running hard all day both days).
- New fuel/water separator. No water inside in the old one.
- Mechanic ran it for 45 minutes hooked up to computer couldn't replicate or see issues. Seems to need full ballast bags/towing wakeboarder to be initiated. Saw a bad cap on a wire and figured that was it. Still had problems afterwards.
- Checked fuel line connections and hoses
- Checked all fluids
- Checked gas cap

Next steps:

- Throttle Position Sensor from this thread (https://forum.supraboats.com/archive...p/t-17067.html) where the person had the exact same issue
- Run external fuel tank (difficult because I have to replicate an issue that takes 1 hour to test)
- Pull fuel tank and lines and inspect inside
- Compression test

Any input would be appreciated. Thanks!

Fuel pressure under load.

Sounds like a clogged filter. I do not see fuel filter on your list of replacements.

The fuel/water separator is the fuel filter unless I am mistaken?

Quote:

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Originally Posted by CornRickey

Fuel pressure under load.

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Diagnosis recommendations? I can think of inspecting fuel tank/lines internally, external fuel tank, fuel pressure monitoring, and/or replacing fuel pump.

Quote:

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Originally Posted by tbs156

The fuel/water separator is the fuel filter unless I am mistaken?

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Nope. 2 different things. The fuel filter is frequently tucked up forward, almost under the floor boards.

Check the fuel pressure when the engine is under load. If pressure drops out of spec then change the filter, same issue after then consider the high pressure fuel pump.

My 03 didn't come with a seperator

Quote:

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Originally Posted by CornRickey

My 03 didn't come with a seperator

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My fuel water separator was located on the aft side of the engine on the port side. It says "fuel/water seperator" WIX #33225. I'll go hunting for a fuel filter. Where is yours located?

Update:

Followed all fuel lines. Only one fuel water separator. On the new one I installed it is printed "fuel water separator/filter".

Ran hand along both lines from tank to to throttle body and fuel pump. After running hand along lines it stank of gasoline. This doesn't seem normal to me. I think the lines and the connections should be replaced.

Installed new Throttle Position Sensor this morning as well.

I noticed when pressure is put on fuel tank, air is released through the gas cap, I assume this is the fuel vent acting as normal. I'm very curious how the air designed to escape through gas cap, because I can not for the life of me see where it would come out.

Next steps: Inspect pickup tube and vent ports. Probably replace fuel lines and connections.

Any ideas how to check fuel tank for gunk, etc? How would you go about cleaning it out if so?