Engine won't start after running and sitting. Vapor lock?

[GA2001Launch]

I have a 2001 Launch with the 5.7L Indmar 350 EFI direct drive. Have enjoyed 10 straight summers of perfect worry free use until this season. When I start my boat up in the mornings and go out everything is fine, but when I park it in the afternoon for a few hours it will not restart. It is as if the engine is deprived of fuel. If it does start, it will barely idle for 10-30 seconds then die. A couple of times it would even start and idle at various speeds by itself before eventually dying. The first time it happened was the first day I had it in the water so I had not changed the fuel filter yet. I bought one during the week and put it on the next Saturday morning before going out. Again it started right up and operated fine all morning, but same problem when I went to run it in the evening. This made me think I had bad gas or water had accumulated in the tank. That week I bought another filter, some HEET water treatment, and topped the tank off with 15 gallons of premium fuel. Added all of these things the next Saturday morning and the boat started right up and ran amazingly well, but same problem when I went to take it out in the evening. I had done some research on the topic and it sounded like vapor lock so I stored it with the clamshell open this time to try to prevent the 'heat soak' but it didn't help.

I have seen various threads on similar things happening but few definitive answers. Everything from vapor lock to bad gas to bad fuel pumps. Hopefully someone in the Supra community can help me nail it down. If it is vapor lock why would it just start to be an issue now? Fuel pumps appear to we working fine also so I would hate to start replacing unncessary parts.

Thanks in advance!

[jzelt]

Is it possible for you to take off your air cleaner, have someone turn the key while you watch the fuel spray out of the jets into the throttle body? Would hopefully eliminate a fuel issue if it is pumping gas and turn more toward spark/electrical which could be more difficult to diagnose.

[CornRickey]

Vapor lock is infrequent in injected motors but possible. I would check the fuel pressure and Mls sure you have adequate pressure when the issue arises. Also you can use a squirt little with fuel in it to see if it will run on it. This will tell you if it is fuel delivery or not. Make sure you have a fire extinguisher on hand.

[lively]

Is this TBI ? If so then u have a electronic fuel pump correct ? Fuel pressure 32 lbs or above ?

Does the motor miss or chug when it is running for those 30 secs , have u tryed to manaually pump fuel ?
Pressure regulator ok ?

There are somethings to check just off hand .. But I have heard of people pulling fuel line and pumping into a bottle to check tell
Tell fuel flow .. Rent a gauge , check pressure

[GA2001Launch]

Yep, EFI system with electronic pump. The motor doesn't miss or chug, it just gradually stops getting fuel then dies. Eventually it doesn't start at all.

I haven't tried manually pumping fuel or testing pressure yet, but I did look at the injectors under the air cleaner and they are spraying just fine when attemping to crank the engine.

Is this TBI ? If so then u have a electronic fuel pump correct ? Fuel pressure 32 lbs or above ?

Does the motor miss or chug when it is running for those 30 secs , have u tryed to manaually pump fuel ?
Pressure regulator ok ?

There are somethings to check just off hand .. But I have heard of people pulling fuel line and pumping into a bottle to check tell
Tell fuel flow .. Rent a gauge , check pressure

[CornRickey]

Resistance increases with heat so if it is a bad connection to start with but still working then gets hot and doesn't then that maybe a issue. Sounds like it isn't a fuel issue though. Get it to act up then check the coil then plugs for spark.

[GA2001Launch]

IZELT - I actually did this last weekend and the injectors are spraying just fine.

If it is a spark/electrical issue why would it only happen a few hours after sitting, then work fine after a day or week of sitting?