Stalls While Driving

Assuming your engine is fuel injected (460s got EFI in the late 80s and it was relatively higher pressure, for the time, not like early low pressure throttle body injected engines).
This alone should all but eliminate vapor lock.
However, there are several other things that could present as the same symtoms.

First though, if it is vapor lock, I believe the boiling point of high octane is a bit higher than low octane gas, so cheap experiment to try a tank of premium, or even premium pure gas.

But I still think vapor lock is about impossible with a 40-50psi fuel system.
Other things:
Old van, old fuel pump? One the fuel pump is heat soaked and that is exaggerated by high ambient temps and also by low fuel levels (less fuel cooling if less volume), it could be losing pressure or shorting out due to heat soak (expansion).
Similarly, it possible for the same to happen to the fuel pump relay although less likely, I think?
Also possible that the ECM is shorting out and losing contact when very heat soaked (had this happen to a boat ECM once).

Is the fuel pump still running (you can hear it) after it stalls?
If not, then I'd lean towards ECM/relay issues, but on a 30 year old vehicle, new relays, fuel pump and filter is not actually throwing parts at a problem, its preventative maintenance.

Bottom line, less likely to be vapor lock on an EFI system than it is to be some other issue.

Fuel injected engines can still experience vapor lock but it is much less prevalent than on carbureted vehicles.

You can try taking off the gas cap to help at the moment. That certainly wont keep it from happening again and again though. Trying to figure out where it is getting hot and trying to due some temperature mitigation in that area would be helpful. Putting in some sort of heat shield in the problem area might work, adding a fuel cooler just prior to the problem area might help as well. Some insulated reflective heat tape wrapped around the fuel line in the engine compartment might also help. It might be worth checking the engine cooling system to make sure it is up to snuff. You said it isn't overheating which is good but is it performing as it should running 10-20 degrees warm might be the tipping point for the fuel but it still not overheat the engine.
The above should help if it is in fact vapor lock and as was mentioned by a previous poster if it is not vapor lock as he mentioned could be several other items including the ignition control, fuel pump etc

theoldwizard1 wrote:
Fuel filter is cheap. Fuel pump is not that expensive either.

Replace it and eliminate that possible cause.

We had a fuel pump fail on a coach we bought that was older and had sat for a few years. Low miles. Our second trip we experienced it stalling out and stopping on the highway. We eventually limped off the highway and got some help. The mechanic said it was the fuel pump and that once the pump cooled down we could drive it for a few miles. Since it was over the weekend, we were able to drive it 12 miles to a campground. The mechanic ordered parts and we returned to him on Monday and he replaced the fuel pump and fuel filter since they were both in the fuel tank. They had to drop the drivetrain, so we asked them to dispose of the fuel left in the tank and put some fresh in it. This was all caused by the coach sitting for years with untreated fuel. For years after our trip where we took it to Alaska, we stored it for 11 months out of the year. We put Seafoam in the tank going into storage every year.

Never another problem and I am still driving the same coach 10 years later.

Dale

theoldwizard1 wrote:
Fuel filter is cheap. Fuel pump is not that expensive either.

Yes they are inexpensive and easy to replace. But if the problem is vapor lock, replacing them won't make a bit of difference.

Fuel filter is cheap. Fuel pump is not that expensive either.

No. Check Engine light is not on.

Thank you! I truly appreciate your comment and information. One mechanic told me that in theory, Fuel Injected engines should not get Vapor Lock.

Thanks again!

Is your check engine light on? Yes/no? Check for fault codes first, before you throw parts at it.

Chum lee

If it's vapor lock, then it is simply that the engine is getting too hot. There are mods to add a scoop (vent) in the hood, add washer fluid squirters and reservoir to squirt water on the front of the engine, etc. Most folks time their driving to cooler times of day, make more frequent rest stops, etc.

Sea Foam won't do anything because there is nothing wrong with the fuel itself.

The fuel pump, fuel filter, ICM, etc, are all possible solutions IF it is NOT vapor lock. They can and will cause stalling, not starting, etc. But if it IS vapor lock then replacing these will not fix the issue.