[Sarna March]

How about wrapping the fuel lines and rails in insulating fiber tape or those mirror-blanket things from engine compartment down to near end of engine block?

The bubbles were the first thing I guessed just reading the thread title.

Of what the bubbles are comprised is a question, for me. If it's air, then it's being introduced somewhere if the fuel tank is well full. If this is only a problem upon encountering heat, it makes me wonder if the injectors themselves are leaking when hot and air is slipping into them and making its way up into where fuel should be, but I don't know the quality of the 1700cc injectors.

If the bubbles are vaporized something in the fuel, trying some pricey racing gasoline to get rid of all fuel that may have low-vapor-temperature whatever in it is one way to diagnose. If the rail temps are supposedly 90°C, then the fuel may be over 100°C in some local zones of the fuel system, which would cause water to vaporize.

But, as I stated, (preferably mirrored) insulating sleeves over the fuel lines and rails would help allay the problem regardless, as if it is mainly a problem when hot, then helping the fuel stay cool just solves it.

https://race.parts/Catalogue/Heat-Insulation/Hose-and-Wire-Protection

 

[Sarna March]

I put some gold heat reflective foil over the fuel lines by the headers and it did seem to alleviate the issue temporarily. Long enough that it gave me false hopes. Ten minutes after that I went to log it and it wouldn’t start again until the rail temps went under 90* or I purged a mason jar of fuel out until no more bubbles. I will be putting a new fuel pump control module in it tomorrow to see if that helps at all. My question now is if the injectors are leaking which they do not seem to be doing because rail pressure stays constant with the ignition off and the car cold, how could air slip into the injector when fuel pressure is staying at 80+ psi, you would think it would leak right?

Yes, if pressure is high, air is not getting IN. However, pressure is staying high and bubbles are forming. I wonder if the pressure is staying high BECAUSE some of the content of the fuel lines is turning into more-voluminous gas bubbles.

But, the foil you are putting on the rails, is it foil with insulating blanket material underneath it? If not, it is reflecting heat but not insulating. I suggest the blanket material with foil on the outside. Here's one that zips up with Velcro:

https://race.parts/Catalogue/Heat-Insulation/Hose-and-Wire-Protection/Express-Sleeve

The product page I directed to has blanket with reflective surfaces, I think.

But, as I said, try a can of the super-high-zoot racing gasoline and see if it solves the problem. If so, your gas has something in it that evaporates too readily, forming bubbles. If it is E-anything gas, then water can become entrained in the fuel by being dissolved by the alcohol, but as distillers know, water can be evaporated directly from the alcohol (or vice versa) by heating the solution.

For you research-minded people, the boiling point of ethanol is only 78.23°C. That is, now that I've looked that up, my suspect for the gaseous substance you find making up the bubbles at 90°C.

 

[Sarna March]

but that is going to be a real pain to thread a fuel line line heat blanket around,

Hence my suggestion to use the zip-up (with Velcro) style of blanket. It is open from one end to the other, evidently, and you wrap it around, then Velcro it shut.

But, the problem, as Linda and at least one other pointed out, is odd and extremely rare.

If you keep cranking the car over, might it get past the air bubbles? I cranked an old pickup truck once for about ten minutes (it had a yellow Optima before they jumped off the quality deep end) until it actually started. I do not recommend this in any way. I, like others, am curious about what the root problem is, being that it is so unheard-of.

If you are truly fanatically scientifically minded, you can collect the gas from the bubbles over time and then analyze it to determine what the bubbles actually ARE.

We're rooting for you, in any case.