Vapor lock hot restarts

My ‘88 with 5.3L has had a hot soak starting issue; once up to normal operating temp and parked for 20 minutes to a hour, will start stall 3 or 4 times. While this is happening, you can hear fuel gurgling in the fuel tank. When it finally stays running, it then has no throttle response for 30 seconds or so, followed by a rough idle for a minute or so.
I assumed this was due to pressure loss in the fuel rail, causing the fuel to vaporize, possibly due to a bad fuel pump check valve or inlet rail pressure regulator.
This doesn’t seem to be related to ambient temperature; today it was in the mid 40s (F) and did it multiple times. I measured the fuel pressure- 32 psi at idle, 38 when the left side regulator vacuum removed. When the engine was shut off hot, the pressure immediately climbed to 38 psi, then gradually dropped to 37 psi and stayed there for 15 minutes. I tried starting and had the start stall 3 or 4 times before it finally idled; at no time did the fuel pressure drop below 32 psi.
I tried putting a bag of ice on the ignition module with no difference; runs fine at all other times and starts fine cold- ideas?

Is there anything screwed into the fitting on the left side of the fuel rail? If so, does it have electrical wires to it or vacuum hoses?

Vacuum lines and it works when tested in a pan of boiling water.

I get this to a milder degree irregardless of ambient temp. Fyi, I don’t have an ac fuel cooler, nor the fuel rail temp switch to increase fuel pressure.

But it is only after trying to start at 15-20 minutes after a shutdown. And it only idles rough and low for about 10 seconds, and then its fine.

Yours sound like a combo between hot fuel trying to get flushed out, and an electrical part being heat soaked. Have you tested coil?

Tested coil, no. Still have the 2 coil system, and runs fine otherwise. Hesitant to throw parts at it, might try a cold compress on the coil.
I have fully functional a/c and the fuel cooler, but it cools the return from the rail to the tank, so logically wouldn’t influence a hot soak start. Likewise the regulator vacuum switch is only functional when there is manifold vacuum (running), again logically wouldn’t affect a hot soak start (although the lack of throttle response and rough idle might be influenced).
After run fan works but only when it is about 90 out.

Has anyone thought of converting to a return-less fuel supply system? There are a number of systems (Holley) that are in-tank pumps with the regulator in the tank. You could thereby remove the surge tank in the boot/trunk, eliminate both regulators under the bonnet/hood, and some hoses. Returnless doesn’t heat the fuel and doesn’t seem prone to vapor lock.

If you have working A/C, and the inline fuel heat exchanger, wouldn’t a recycling system keep the fuel cooler?

A/C works on mine; the issue is on a hot soak restart. Fuel isn’t circulating when the engine isn’t running and cooler isn’t cooling.

So how would a return less system make any difference in this case?

Don’t know that it would make a difference, that is why I am asking. Pretty much all EFI vehicles since the mid 90s use returnless fuel supply systems. Must be a reason…unless it is just cost.

I would think that a returnless system would require a pressure sensor at the rail and a variable output pump controlled to hold the desired pressure at the rail. Is that what these newer systems do? You certainly wouldn’t want to deadhead 300 hp worth of flow while driving a constant 55 mph down a country road.

I see two possibilities.

  1. Extensive research showed significant advantages in a returnless fuel system - increased performance, it’s more reliable, easier to service, environmentally friendly, weight saving and new shiny.
  2. It’s cheaper.

If it involves a closed-loop pressure control system and a variable-speed pump, it would save a little energy. Could that be the impetus?

Of course, it also saves return lines. That’s a bit of money, but it must be balanced against a pressure sensor, a variable-speed pump, and the associated control system. But I suppose you also do away with the mechanical FPR’s. Probably a job for an accountant to figure out the savings.

Some use a sensor, then PWM the pump. Others use a mechanical regulator that just dumps the excess back into the swirl pot; that is what I have in my Rover V8 MGB- I used a Chrysler minivan returnless fuel pump. I still have a regulator at the rail, though, as pump is 3 bar and injection system is 2.5 bar. Never vapor locks, though…

OK, I’m confused. What do you mean by “swirl pot” in this context?

Most in tank EFI pumps have a dam or reservoir around the pickup to prevent fuel starvation when level is low or on turns. The return or regulator vents into this to ensure that the pickup always is submersed in fuel.
Plastic tanks have it molded in, steel tanks usually are baffles or a pot shaped tub.

I am very keen to hear the solution!
How about bad, old (loss of octane), or watered-down fuel in the tank?

I don’t believe cost was a factor. The additional sensors and variable fuel pumps cost more than the old design.
The primary reason was to reduce EVAP emissions form the fuel systems.

I am sure you are correct.

Daily driver, so old fuel not an issue. It has always had the problem (well, as long as I have owned it, just worse over the last year). Possibly ethanol or additive related, don’t know.