Ive got an 84 -SE, with about 220k on it, almost completely stock. Something with the fuel/vent system is giving me troubles.

I live it vegas, it get stupid hot here, and when I go home from work, after the car was baked all day, I get a high pitched hissing/whining noise from the back of the car. Its done this for 2 years now, usually when Im under 1/2 a tank. Never been a problem. I figured it was just a partially blocked vent, and when the tank got hot and pressurized, air was squeeking through the vent, thats what it sounds like. The noise goes away abour 30 seconds after I shut her down. Today, while the car was running, it occured to me that the noise could be the gas cap leaking fumes. So, I took the cap off while it was running, to see if it would stop. I took the cap off, an incredibly large amount of pressure was released, the noise stopped, and then the car died.

Now, it wont start. I turn the key on, hear the pump come on, but the tone is different, like it cant catch its prime. The car will start and then immediatly die. The pumps whine fluctates, sounds like it catches prime for a second and then drops off.

What did I do? I know the evap/charcoal canister system ties into the engine vacuum, when I took the cap off, did I create a massive vacuum leak? Did I somehow put a bubble in the line? It would still start with a bubble though.

I should say, that in the past 3 months, it wouldnt start for me, twice. Both times when it was really hot. It would just crank and crank, and not catch, like the motor was down on compression. But it would compression start easily, run great, idle and plently of power, and start up again if I shut it down right away, with no problems.

The pump is a newer (~3-4 years) carter, both filters are less than a year old.

what gives?

 

This is very similar to the problem I've been having. https://www.rx7club.com/1st-generation-specific-1979-1985-18/gsl-se-vapor-lock-960963/

 

sounds like the fuel pick up tube is corroded at around the fuel level you are hearing the noise at. drop the tank and pull the sender/pick up tube and inspect very closley, bet it has a pin hole in it.

 

^^could very well be. i would also reccomend dropping the tank and inspecting the pickup tube. inspect it for partial blockage or any corrosion. you should also inspect the pickup filter while the pickup is out. i'm not sure how the pickup can rot inside of the tank but i've seen worse happen.

 

I dont see how that could cause excessive pressure build up in the tank. Also, the noise continues for a bit after the car is shut down.

And why did the car die when I took the cap off? Thats tripping me out.

 

IIRC these cars run a return style fuel system, perhaps releasing the pressure at the tank had some impact at the fuel rail? Did you try priming the pump several times (key to on, off, on, off, on) before attempting to restart?

edit: Releasing pressure from the filler cap would produce a great deal of vacuum/negative pressure at that location. Maybe when you released it, it pulled fuel in the lines (before the pump) back into the tank. When this happened, the engine shut off. Without fuel there, the pump would not be able to prime effectively, so it would not restart. /theory

 

its normal for there to be pressure in the tank. i worry if i remove the gas cap on my 7's after a drive and there is no "whoosh" of pressure. this would make me believe that theres a pin hole in the gas tank.

 

since 2007 I fill my gas tank while the car is running, never has the motor shut down when i open the lid, and yes it always makes that whoosh when you twist the gas cap

 

That makes sense. I let the car sit for an hour and it started right up and ran great. I bet i put a big vacuum on the tank when I popped the cap.

I know there is supposed to be some release of pressure, but this was intense, much more than normal. Ive popped the cap when there was 3/4 tank, and it whooshed so bad it spit fuel out. I still think there is a plugged vent or something to that effect. Maybe a worn charcoal canister. 220k might do that.