75TS Fuel Vapour/Vent/PCV system

[ALF750]

Hi all, Im after some/any info on the workings of the fuel vent system in the 75TS if able.   Specifically, what does the front canister do, and what the solenoid valve near the two coils is for?   The reason I ask is that whenever I open my fuel cap there seems to be a significant vacuum in the tank.   I would have thought the one way valve in the boot near the plastic tank would have relieved this vacuum?   I've checked the one way valve does, and that it is in the right way, and that all lines are free of blockage.   Seems to me that the fuel pump has its work cut out already without fighting a vacuum in the tank.   Any thoughts?

[GTVeloce]

Fuel vapour goes through a separator (plastic tank which may be blocked) before the one way valve. Liquid is drained back to the tank and the vapour goes through a plastic pipe that runs to the front of the car, specifically the charcoal cannister. When the ECU registers revs above idle, it opens the solenoid valve which draws air (vacuum) from the intake plenum which sucks from the charcoal cannister. So in theory, the petrol vapour is then sucked through the charcoal and into the intake and burnt.

Start by checking all the connections are correct and tight. Then I would remove the plastic tank and clean it out thoroughly. I used a solvent (petrol) and thin wire to make sure the small aperture is free. Then start on the front section.

Do you get a petrol smell anywhere? It may indicate a leak in the system somewhere. Less likely given the vacuum.

[ALF750]

Thanks GTVeloce, I'll pull the tank and clean it.   No fuel smells, everything lloks in good condition externally.

[ALF750]

just an update to share info.   I miss-posted about 75TS fuel pumps in the 116 system, but thought I'd wrap it all up here as the vent system and pumps seem related to me.   The one-way vent valve in the boot seemed OK, but was sticky, so it has been replaced and vacuum in the tank after running seems much reduced now.   Vent lines and their function to the inlet manifold is also OK.   I pulled the in-tank fuel pump out and found the pos wire was broken and looked like it would always have been at least 50mm too short to reach the pump terminal??   How and when this happenned I do not know, possibly at manufacture?   This problem has been a long-running one.   Anyhow, I replaced ther wire and pump, gave it a wet test run outside the tank then re-installed it.   On test drive there was still an occasional hesitation over bumps, and this could be repeated by tapping main pump with hammer when idling.  So I replaced it also and for now all seems good.   I think several problems combined here:   in-tank pump was never working, vent system placed additional strain on main pump, which was doing all the work anyway, so would regularly pack it in whe nhot and under load.   Maybe high load on this pump placed additional current draw on white/pink wire, causing/aggravating the known TS problem.   Fingers crossed:)