Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Fuel tank vacum

I am enjoying the 2006 4/4 l bought last year especially in the current weather however there is one thing I don't understand.

I tend to let the fuel tank to drop to less than 1/4 before topping up and am surprised at the vacuum when I remove the fuel cap. Not only do I need to pull the cap out but the rush of air in sometimes results in the tank pinning as it no doubt springs back to shape. Is this normal? The car was fitted with a longer range tank before purchase?

Thanks

Check this thread out - no it's far from normal your symptoms and need sorting before tank damage occurs. I don't recall Craig reporting back with the factories findings which would have been useful for others.


http://www.talkmorgan.com/ubbthreads.php/topics/517308/1

I've seen these symptoms reported by others but if there is that much vacuum how will the pump deliver enough pressure to the injectors to run smoothly and without power loss.

If I had to guess, I would say this has something to do with the EVAP system because that is what acts as the fuel tank breather in modern engines and if the valve is not working properly maybe it can close off the breather.

Just a thought, no evidence.

I suffered with this problem which IMO caused my fuel tank to split at high level on the weld joint.

Once the tank was replaced by the dealer (under warranty) this caused further pressure issues which resulted in me being sprayed with fuel when I released the filler cap, it was worse when the tank was low on fuel. Some TM’s say a rush of air is normal, however the factor say it is NOT. Slight air release maybe yes, is ok.

The factory did fix my car after approx 4 days, the problem was a kink in the line somewhere, and the roll over valve being replaced and repositioned.

This is quite a rare problem (so I’m told) And more problematic on Sport models due to no spare wheel, as the side screen storage tray sometimes obstructs the fuel tank pipes etc.

I’m no mechanic, It’s info received from dealer and factory

The factory treated me very well, and also arranged to have my car collected.

I had a longtime fuel smelling and leaking problem and got also sprayed with petrol during the last summer.

The reason was a buckled petrol hose between the petrol tank and the roll over valve on top of the tank. The underlying cause was a broken bracket of the roll over valve. Subsequently the pressure in the petrol tank is encreased.

Now I‘ve fixed the roll over valve and renewed the petrol hose - all problems are solved since I made this modification.

A rush of air due to vacuum in the tank when filler cap opened can't possibly be normal and needs immediate investigation. Rollover valves, carbon filters and associated pipework are first areas to investigate.

Note that by its very nature and function the carbon filter will allow a very slight vacuum in tank as fuel is consumed - not enough to cause a rush of air though.

After filling up yesterday I drove 150 miles and on removing the fuel cap there was no noticeable vacuum.

As a new owner I am still finding my way around the car and without the help of a Haynes manual I would be grateful if someone could point me in the direction of the roll over valve and the EVAP system and what to look out for

The car is a 2006 4/4 70th anniversary edition with a 1.8 Duratec engine.

Thanks

I've got a parts manual for these cars - if it would help I can send it to you if you PM me with your private email. It's a pdf file is the reason.
It's not a Haynes manual but will help with identification of the various parts of the fuel system.

Good luck.

I don't think this subject is straightforward. All my MGBs had a fuel tank vacuum way back in the seventies. I believe that the tanks were designed to vent through the cap, and I suspect current Morgans may be similar. On my MGBs I made a small hacksaw cut in the filler neck to allow better venting, but I think the idea was originally to stop fumes venting from the tank.

My Roadster doesn't seem to have a tank vacuum, but my Plus 4 does have this when I go from a full tank to a quarter tank, then release the cap. I don't really worry about it.

Our wedding photographer bought a new Lancia Beta, and within a week, the vacuum had sucked the tank so far in that it would only hold a gallon........

Dave, you are correct this subject isn’t straightforward when ECU’s and EVAP systems are involved.

Our modern Morgan’s don’t have vented fuel caps like older cars.



https://www.samarins.com/glossary/vent-valve.html