I just reread the whole thread & see we had already discussed the relays, sorry about that. I'm going to try & cover all the bases in this post & will be repeating (again) some of the things we already covered. If I can give you enough info you should be able to solve this next time the problem occurs.
I doubt if taking it to a garage while ití* running will do any good. Anything they could check is going to be working.
I looked at a wiring diagram again & Vats would disable the starter. Vats should also never be an issue for a car stalling.
Swapping the relays should have pretty much ruled them out.
When the key is turned to the run position the pump gets power just for a couple seconds to pressurize the fuel rail. Thatí* why I said we couldnít be sure the pump wasnít getting power without knowing how the mechanic checked it. If he checked for power with the key in the start position we could be pretty sure that the pump wasnít getting power. He also would have had to check using the same ground the fuel pump uses.
There are 2 ways to check for fuel pressure. The best & safest way is with a fuel pressure gauge. They cost about $40 & hook up to a Schrader valve on the fuel rail. The other way is to remove the cap from the Schrader valve & press the center of the valve with a small object. Which ever way you choose to check you need to put rags around the valve to catch any leaking fuel. If the pump is working there will about 50 pounds of pressure at the rail. Using the second method can spray fuel all over you and the hot engine. Youíll need to position your hands & the rags so the fuel doesnít hit you in the face. Whichever method you use you should practice while the engine is cold. If you get gasoline on the engine donít start it up until it has a chance to evaporate.
Assuming the car has stalled & has no pressure at the fuel rail youíll now need to check for power going to the fuel pump. You can check this with a light bulb or voltmeter. You should find a test lead (gray?) between the battery and fender. You can connect a 12 volt light bulb or voltmeter between the test lead & the negative battery terminal. If you are by yourself when the car stalls you probably wonít be able to use a voltmeter. I made up a test light by soldering a 12v light bulb to a lamp cord that is about 6 feet long. I then connected an alligator clip to one of the other ends of the wire and soldered the other wire to prevent fraying. Now just push the soldered end into the test lead & hook the alligator clip to the negative battery terminal. The cord will be long enough to place the light bulb on the passenger seat. Bulb should light for a couple seconds with key in run position & stay lit while cranking. If the bulb lights up the fuel pump or the fuel pump ground is bad.
If the pump is not getting power youíll need to see if youíre getting power from the PCM to energize the relay & check for power at the relay for the pump. Remove the fuel pump relay. On the bottom of the relay there should be 4 numbers 85, 86, 87 & 30. Connect the alligator clip to the negative battery terminal & the soldered end to where prong #30 would normally be. Most likely this one will be fine. Now check where prong #85 would be. You may have to turn the key off then back on. Iím not sure if the light will come on for a couple seconds or stay on. Also check with key in start position. If the light comes on move the wire from the negative battery terminal to where prong #86 would be. If the light doesnít come on now the ground for the relay is bad. If the light comes on try to start with a third relay. If the light doesnít come on weíll need someone with a factory service manual to tell us under what conditions the PCM wonít send power to the relay.
I know this probably sounds complicated but ití* really not that hard to do. Ití* a step by step procedure thatíll get you the answer to the problem if it is indeed fuel related.
If the engine quits again before you get a chance to rig up a test light try kicking the carpet where the ground busses are located. Maybe youíll get lucky.
The bulb I used is a GE 90. It'* a single filament bulb with both contacts on the bottom. Tape bottom of bulb before using.
PS. I still need to proofread this. Edit - Proofreading done.