Not sure if this is accurate, so I posted this response to see what people think.

It seems to me, based on what I've read on 'vapor lock' & 'main relays' and from personal experiences in what I've had to do to get my car that was just running but then would not start again after a short run (namely, having to open the hood, doors, and blow the heater and wait 20 minutes)...I'm inclined to believe that these two problems have the same symptoms and both can be solved simply by letting interior & exterior heat dissipate.

Though my car is equipped with a fuel injector ('91 honda accord 4-door sedan lx) I'm pretty sure my problem is vapor lock and not a bad relay, though I have reasons to suspect both. Simply because I don't want to spend money and rather take initiatives to try avoid 'vapor lock', I'll just stick to not doing anything about it.

What'ch'all think?

 

There's one big important difference.

With a bad main relay the fuel pump will not be running. Vapor-lock happens with the pump running.

If the fuel pump is running during a no-start episode, then vapor-lock is a possibility.
If the fuel pump is running, then it cannot be a bad main relay.

If the fuel pump is not running it's vice-versa.

Most of the time, I hope, people suggest you listen for the pump running (or not running) when you suspect this.

 

Vapor lock is unlikely IMO. Fuel is shuttled round trip from tank, fuel rail, back to tank, and has a very short residence time to heat and form bubbles. This problem has never come up in all the posts I've read here.

However MFR and ignition switch assy are constant problems.

good luck

 

Off the end here as I didn;t re-read the whole thread. The "set-up" on some of the 6th gen v6's....well did lead to vapor lock issues.

Now if we are talking about something other than a 6th gen v6....vapor lock is out of the conversation.

 

Non-return fuel systems like 2003+ Accord 4-cyl also do not have a return line with constant circulation. But they are pressurized so that is very different from the old-type system on carbureted cars with suction pump located on the engine.

Vapor-lock requires the fuel's vapor pressure larger than the line pressure, so it evaporated in the fuel lines. Then the suction side of the pump cavitates & nothing gets pumped. When this happens, the pump doesn't stop "running". So an electric fuel pump will still make humming noise while cavitating. That's why listening for the fuel pump running will tell the difference between vapor-lock vs. a problem with the main relay.