Thread: 1989 Range Rover Classic fuel tank breather system - issue

Venting (outwards) of petrol tanks is supposed to happen via the charcoal canister, connected to the inlet manifold via a purge valve. You might have to find a 3.9 Rangie and copy the plumbing. Keeping some pressure in the fuel tank stops your fuel evaporating away in hot weather, and reduces condensation forming inside the tank in cold weather.

I second checking the charcoal canister.

I had tank pressure/venting issues with mine (Previous owner converted from carb to throttle body injection and they bypassed the charcoal canister and the tanked vented by purging neat fuel!). When I did plumb in the charcoal canister, I got symptoms like suction when opening the fuel filler to sucking fuel through the charcoal canister and flooding the engine. Eventually resolved the issue to be a valve that was faulty in the charcoal canister. Swapped it out and it's all good now.

Not sure which canister you have, but I got a Toyota Prado or Soarer one and it was an exact swap - mounts etc all lined up!

I've got pressure build up in the tank not suction. When I tank the fuel cap off, there is pressure blowing air out the opening. The charcoal canister (cylinder type) is plumbed in although the pipe doesn't go to the inlet manifold. It's a long range that if that makes any difference. I'll have to remove the side tank to check the valve at the top of it prior to it going to the canister.

Dads 92 RRC has the purge valve up near the canister, but mine doesn't. The pipe from the back goes in then another goes out, there appear to be one way valves in the lines from the back side tank to the canister as I can't blow air from the canister end back.

Pressure build up is completely normal of course, especially in warm climates. I'd actually be worried if there was no build up, you'd have a broken breather hose or a damaged cap seal. Also the cap is spring loaded, anything more than normal vapour pressure just lifts it off its seal and vents the excess.