hcr32 fuel tank pressure problem

[smart_garrett]

Hello all, 

Quick background info so last time I was at an test day for my circuit race car, i went in to pit for a fuel up. When i opened it fuel cap TONS of pressure rushed out for maybe 10 seconds, enough to wet a crewmans hand from the vapor. Thought it was strange but filled up the car after spilling some as the pressure was pushing the gas out of the nozzle and out of the side, anyways it died down and was able to fill the tank. When i went to crank over the car to go back out, it wouldn't fire, like it was getting no fuel. I pulled out the laptop and changed the fuel pump prime time to 8 seconds and it then fired up. I'm wondering if the fuel tank roll over protection value is clogged? The car has no charcoal canister and is vented to atmosphere. I'm not even sure where the roll over valve is but I saw online you can only buy ones for an early series car which mine isn't. So I will probably just get a universal rollover value and use that. Any input?

[SteveL]

Mechanical roll-over valves are a very simple devices.....a ball valve that is normally always open but in a roll-over the ball rolls to the other end of the valve and blocks off the hose/pipe whatever.     There's no spring, they rely on gravity.      I'd be surprised if that was the problem, but it depends on the design of the system......has the valve been installed properly in the first place ?      Clearly the system is not venting properly for some reason, so a thorough inspection is really the only way to go.    The amount of pressure you're describing is definitely not normal.

Of course, the above assumes that you don't have one of the fancy electrical roll-over protection systems. 

[TurboTapin]

HCR32 roll over valve is tucked in behind the rear diff. It's in the center and can be somewhat easily seen if you're under it. NIssan still makes them and they are roughly 80$.

If it's not that then it's the short ~18" hose between the tank port and the roll over valve that is blocked. Ether way, should be an easy fix.

Cheers. 

[SteveL]

That's not the sort of 'roll-over valve' anyone should be using in a race car.

[smart_garrett]

2 hours ago, SteveL said:

That's not the sort of 'roll-over valve' anyone should be using in a race car.

Yea, I haven't fooled with the valve myself. Stock tank is going to be swapped for a cell, but I'm trying to get this issue resolved to test other things. I know some Audis of the early 2000's had a mech-type roll over valve and some people had problems with those sticking, so thought it could be similar. Anyways, I'm probably just going to drop the tank again and poke around.

[TurboTapin]

2 minutes ago, smart_garrett said:

Yea, I haven't fooled with the valve myself. Stock tank is going to be swapped for a cell, but I'm trying to get this issue resolved to test other things. I know some Audis of the early 2000's had a mech-type roll over valve and some people had problems with those sticking, so thought it could be similar. Anyways, I'm probably just going to drop the tank again and poke around.

There's no need to drop the tank to verify the tank vent, hoses, roll over valve, etc. You have access through the trunk fuel pump hatch. 

Edited April 25, 2021 by TurboTapin