fuel tank pressurisation

Right now I've got the van running again it runs rough after a couple of mins now it was low on petrol so I nipped down to the local esso to pop a drop in and when I took the filler cap of it released a load of air is this normal on a hijet? as it isn't on everything else! can't see the open end of the tank vent pipe to check its clear and it doesnt seem to be the cause of rough running as drove around the car park without the cap on.

Rich.

Yes this is normal as it has a carbon filter thingy to save the vapours of fuel so that it is supposed to be more economical!. Don't know whether it really makes much of a difference or not.

Ta I normally avoid Injection cars and bikes as they are a pain to fix, carbs are so much simpler to sort out if you get stuck with no tools, last summer I bodged my car to drive home from somerset on 3 cylinders (out of 4) after the cam belt snapped and bent a valve a ecu would have had a fit with what I did but the journey only took 2 extra hours and that was mainly on back roads just in case. anyway back on subject the manual don't say about tank pressure and the rough running I'm getting feels like fuel starvation but I checked the plugs and they were very sooty so am just working my way through all the bits I can think of that cause rough running the only other thing that I have now which I didn't is a sort of hissing sound that I can't pin point as sounds like its coming through the vents when driving

Rich.

Mmmmm. Strange!!

When you say "rough running" what are you experiencing?

I don't think the tank should ever hold.
"In a typical system, vapors from the fuel tank and carburetor bowl vent (on carbureted vehicles) are ducted to canisters containing activated carbon. The vapors are adsorbed within the canister, and during certain engine operational modes fresh air is drawn through the canister, pulling the vapor into the engine, where it is burned."

Also, fuel tanks tend to have a "air in" valve so as you use the petrolin the tank fresh air is pulled in to stop the vacume effect. If we didn't have these breathers the tank pressure would change altering the fuel line pressure thus altering the injector rail target pressure determined by the fuel pressure regulator.

rich the mechanic wrote:Ta I normally avoid Injection cars and bikes as they are a pain to fix, carbs are so much simpler to sort out

I disagree, Efi is far more effective and is much easier to fix. I know my dad feels the same as you though! Carbs just seem so primative, they are so hit and miss. If you've got some crap in the jets they may still run but may be causing loads of damage. At least the EFi system measures its own accuracy and changes the fueling as the weather changes.

I'm the same as Rich I'm afraid - carbs anyday! The electronics on 'modern' cars just aren't up to the job and they preclude 99% of us from working on our own vehicles. I've never had a fault on my bike that I haven't been able to fix.

The wife's bloddy car is another matter entirely! For the last four years we've been driving around with the 'fault indicator light' lit on the dashboard. It's been back to the dealers so many times I've lost count. All we ever get is 'there's probably a fault in the ecu loom, perhaps a dry joint or something' and 'we're chasing a phantom, there's nothing we can do about it sorry' - don't worry as long as it doesn't start to flash.................

If it had carbs a. I wouldn't have this problem and b. there wouldn't any dam light lit on the dash board!!!

Del Orto's any time

I agree that EFI gives the best efficiancy and economy but can you fix it at the side of the road with a screwdriver and a stick The van rough running isn't the tank pressure as I used a universal cap and a spoke to keep the splash valve open and didn't make the slightest difference so testing all the ignition bits are up next as I've never had a triple before the best way I can describe the feeling when driving is like going down to 3 out of 4 cylinders when under load, Idle, free reving and down hill feels normal.

Rich.