My gas tank is building up pressure. I have to take the gas cap off every few days to bleed the pressure. It's so bad some times the cap, once free from the threads will fly off. Any ideas what is causeing this pressure build up?

 

Welcome to the world of Fuel Injected cars... it is quite normal, really.

The pressure is caused by the higher pressure of the electric fuel pump, higher pressure that is required to keep the injectors flowing. The fuel return does its thing, and the end result is a pressure build up in the tank. The stored pressure is vented, sorta, through the charcoal canister. You may have a problem with your canister, tho, if the pressure is too high.

Blowing the cap out of your hand is pressure. Check the canister...

 

From what I know that's definatley not normal. You should have vacuum not pressure. Any ideas?

 

There was a post a couple of weeks ago (maybe last week) about someone that had this sort of problem. It turned out their canister was completely gone, and the fuel return line from the canister was competely plugged with rust.

Look in the past posts, he might have turned it into a tech tip as well. It scarred me enough that I went right out and made sure my canister wasn't falling apart. This weekend (if it doesn't rain too much) while I'm doing the brakes on the other cars I'm going to check and see if I can blow thru the lines.

 

thanks guys. Could this be casuing running problems. I notice the car not running as well when the pressure is built up. :confused:

 

Yeah there was a guy who's tank was getting HOT! from a clogged return line from the canister to the tank.Seems when you go repairing things the lines that were left unhooked for years have had bugs or dirt get in them. :chevy

 

My 85 had the same problem. Check the small vacumn actuated valve thats in "the line" just before the canister. mine would not open so the tank fumes would never get sucked in the canister and back into the engine to be burned. If you suck on the small line lightly you will here it open and you will be able to blow or suck thru the larger line easily. NOTE: All blowing and sucking should be done with friend :D


[Modified by djpearn, 6:29 PM 8/9/2001]

 

Im the one who posted last month about the vapor problemm,Hot Gas Tank and too much pressure....too much pressure is dangerous...I had the same symptoms where the gas cap would want to fly off when loosening..if this happens after a drive for a while, and you touch the gas tank under the bumper, it can get very hot...I almost burned my hand touching it when I went to see if it was hot or not.

Heres the link for the problem I had and how i fixed it.
http://www.corvetteforum.cc:88/zerothread?id=93566

I highly suggest you use compressed air starting from the tank and unhook the rubber lines under the car from the steel line and see if compressed air will pass through.(This is how I found my line was clogged.)

Then see if air will pass through the steel line under the car to the front of the engine.
Check each section of line until youre up front to where ever the vapor line is supposed to vent the gas fumes.

Not sure if youre 88 is a little different then my 86 set up as far as where the vapor lines go.

Since I replaced the canister, rubber hoses and the clogged steel line, i have NO more high pressure back there like before...gas tank doesnt heat up anymore.
After driving around for a good while then get home, it will barely even hiss when I take the cap off to check it..before the fix it was Hissing so loud and hard the gas cap wanted to fly across the street when I took it off.

Get this fixed asap...its a disaster waiting to happen.

Im glad it didnt explode on me.

 

This could cause running problems also. The tank being under that much pressure will affect the fuel delivery rate for the engine. That much pressure to blow the cap out of your hand is an accident waiting to happen. :eek:

 

Thanks again guys. I had no idea it was not safe. I did have to replace that little black valve thing. This was done a few months ago, and it did help, but didin't fix it. SO, I guess it's safe to say it lies within the caister area. I'll haveto just test everything until I find what's bad. Thanks again