mk1 fuel tank baffling?

[jsvr6nsd]

I am wondering if mk1 fuel tanks have any baffling. I have a 84 gti 1.8L JH with no mods to speak of. I am noticing that when I go uphill with anything less than a full tank of gas I start to get hesitation. It only occurs when going uphill no other time. I asked this in other forums, but still haven't found an answer.

I'm baffled.

[antichristonwheels]

maybe you want to pull the back seat and take peek.

[Fat Rabbit]

MK 1 fuel tanks have a known issue with the pick-up tubes in their fuel tanks which usually exhibits itself when cornering with under 1/2 tank of fuel. You might be experiencing a variation of that issue. The usual solution is to replace the fuel tank. A new fuel tank costs $150-$175.

You also might want to follow the advice of "antichristonwheels" and take a peek inside the tank. The tank migh be loaded with crud that under certain conditions causes fuel pick-up issues.

One of the most difficult fuel reated issues I have ever found involved a damaged fuel line that would suck air under certain conditions. It took me a long time to find that issue because it would not occur with any regularity. Your car may have something similar. Your car might also have a bad gravity valve. The gravity valve allows the fuel system to take in make-up air yet prevents spillage and controls emissions. Easy to check -- leave the fuel cap loose so the tank can pull in air to replace the gas used. FR

[jsvr6nsd]

MK 1 fuel tanks have a known issue with the pick-up tubes in their fuel tanks which usually exhibits itself when cornering with under 1/2 tank of fuel. You might be experiencing a variation of that issue. The usual solution is to replace the fuel tank. A new fuel tank costs $150-$175.

You also might want to follow the advice of "antichristonwheels" and take a peek inside the tank. The tank migh be loaded with crud that under certain conditions causes fuel pick-up issues.

One of the most difficult fuel reated issues I have ever found involved a damaged fuel line that would suck air under certain conditions. It took me a long time to find that issue because it would not occur with any regularity. Your car may have something similar. Your car might also have a bad gravity valve. The gravity valve allows the fuel system to take in make-up air yet prevents spillage and controls emissions. Easy to check -- leave the fuel cap loose so the tank can pull in air to replace the gas used. FR

So drive it under the same conditions that it was happening without the fuel cap on and see if it happens? Ok and if it does not then the gravity valve is bad. Where is that located?

[Fat Rabbit]

Yes - take the car for a drive under the same uphill conditions except with the gas tank not sealed. The gravity vent valve is up under the rear fender near the fuel fill pipe. That valve connects to the emissions evaporative system and the fuel tank. It is a quick no-cost check although I think your solution will be found in the gas tank itself. FR

[jsvr6nsd]

Yes - take the car for a drive under the same uphill conditions except with the gas tank not sealed. The gravity vent valve is up under the rear fender near the fuel fill pipe. That valve connects to the emissions evaporative system and the fuel tank. It is a quick no-cost check although I think your solution will be found in the gas tank itself. FR

Well I removed the cap and drove it... no hesitation or anything. Now where do I get a new gravity vent valve or do I just remove it?s

[Fat Rabbit]

Try a junkyard. You also might pull the old one and see if you can make it operate.

The valve has to be positioned up and down so it vents when the car is upright and shuts off when the car rolls over.

The valve is one part of the evaporative vapor recovery system. The gasoline vapors travel to the front of the car where they expand into a tank, pass through a charcoal filter and eventually get burned in the engine. You could just disconnect it but the car would then be out of environmental compliance and I would not want to be in a car that would leak gas in a rollover situation. FR

[jsvr6nsd]

Any chance you could get a pic out of a Bentley manual for me so that I can see the valve?