1991 GTA 355. Nothing stock but the block.
After driving the car around for an hour or more on a warm day(80 degrees and up), the fuel pump begins screaming and the tank pressurizes because the fuel is getting hot and boiling. I made sure the heatshield above the muffler is in place, as is the one for the exhaust pipe right before the muffler too. I dont see any place or way for this to be happening since ive got the heatshields in place and everything. I dont see a place where the lines should be getting that hot either. this is a problem that popped up after I rebuilt the engine and did a ton of other things. I've been slowly trying to figure it out now for 6 years, and im kinda stumped now I think. I thought i had it fixed after putting a heatshield on i missed, but it happened again a few days ago, so I guess not. Last trick I can think of is maybe try to lower the muffler down just a tad further from tank.
Any ideas would be great.

 

Are you running a return line? These tanks have always built pressure when running. What is the state of your fuel pump vent? Does the engine run different? If the motor is running normal I doubt you are having vapor lock. The pump could be on its way out.

 

Pump is new and meant for a gmc syclone. K&n fuel filter, adj regulator set at stock pressure, all lines are stock. You can hear the fuel boiling at times, and when you pop the cap while it's happening it let's off a hell of a burst. It doesn't usually change how it runs, but it did kill the car once and make me let it cool down when it first started. I changed out an already new pump after that not knowing what was happening, and it still does it.
Im wondering if the tune has my exhaust running too hot or something. Im out of ideas.

 

fuel boiling doesnt seem close to being correct

 

No way.
You're talking about heating up to 15 gallons of fuel, up to boiling temps, while the fuel is simultaneously shedding heat through the majority of the fuel lines, all of the surface area of the tank....no. There is some other, actual problem that needs diagnosing here.

 

Yep, im aware and thats why im here. The exhaust is not contacting the heatshields, everything seems to be as it should, it runs great, so I have no clue here.

 

The pump is probably on the way out. Especially if it's a new old stock unit. Excessive pressure is annoying but a common factor on these cars. We all have it. I'm running true duals where my fuel lines and mufflers are all around the tank and I don't have any issues. Pressure yes, but nothing more.

 

I had a similar issue w my fuel sounding like it was boiling. I checked the tank temp w a heat gun and it was 115 deg but the car ran fine. This was on a 88deg day after driving for a hour. The fuel pump was new. There was lots of pressure when I removed the gas cap and there was a bubbling sound coming from around the tank. In the end I think it was fuel in the vent hose. There is nothing stock on my car. I have an in tank aeromotive pump, 6 an lines and a pro Flow xt efi/intake. My fuel lines are run along the valve covers/fuel rails. I put reflective insulation on the lines all over the engine and it did drop temps a bit. My muffler is 2 (ish) inches from the heat shield. I now have 2 huge spal fans moving air also. After driving a bit I have fuel tank temps from 95-105ish on a hot day. I also try and keep the tank pretty full, it totally runs cooler that way. I don't know what contributes more heat, the engine heating the returned fuel or the muffler. I know the pump contributed but I assume it's an insignificant amount.

 

2 pumps in a row though? i replaced the brand new days old pump the first time it did this because it was hardly running when it happened and i wasnt sure what was going on, but then the second pump did it too on the first hot day, just now it keeps running fine when the pump starts squealing. After putting on the heatshields that were missing the first time around it got better and takes longer for the problem to occur, but it still does it. You can feel the filler neck is definitely warm around the gas cap too.

 

Im pretty sure I barely have an inch between my heatshield and muffler. I have the stock dual fans, but they are both on by 175 and the engine and trans keep perfectly cool. Im thinking I need to drop the exhaust down a tad.

 

What pump are you running? OEM GM units? What pressure does your combo need (assuming 58psi?). Did you replace the pump with the same thing?

 

im running 43 psi, and yes oem style pumps. I dont think the first pump was the same and since i thought it failed, i got a different one. I know the one in it now was meant for a syclone or TTA. It was an exact fit, just flows more.

 

Why don't you just measure a few things....and find out what's going on?? What IS the temp of your fuel/tank after an hour? What IS your fuel pressure? When the symptom is occurring?

It could be a bad second pump. It could be boiling gas. It could be whatever..... We can guess all day long....won't help solve anything though. If you really think that your gas is boiling, then get it "boiling" and shoot the thing w/a temp gun, and SEE. It's not boiling...but at least if you measure something, you'll SEE that it's not boiling and you can move on to more rational possible causes and diagnose those.