Had this scary experience happen w. Superblue at the last two fill-ups at the gas station. Keep in mind, these both occurred during hot weather, and when the tank was very low on fuel (if that makes a difference)
I went to remove the fuel cap, and Superblue very forcibly âfartedâ though her fuel filler opening at me - both times with enough force that it would have blown her fuel cap out of my hand but for the fact it was still engaged in some of the threads of the fill tube opening.
WTH ???
I remember reading in the archives sometime back about the Rochester valve in the emissions system going amiss, but, IIRC, the opposite reaction happened - i.e. air rushed INTO the filler opening upon removing the fuel cap, apparently to fill a vacuum state existing in the tank at the time the fuel cap was removed (and, in worst case situations, the vacuum created inside the tank resulting in an implosion/crumpling of same ).
So whatâs going on here? Is it something to be worried about? Or does this just sometimes happen if the fuel level gets low enough in very hot weather?
In the meantime, I have made sure to not fully seat her fuel cap, leaving it slightly âopenâ.
Something I just thought about ⌠is the flaw something to do with her fuel cap? Are they supposed to actually seal 100% tight, or have some âflexibilityâ inherent in them in order to allow air to escape if it gets above a certain pressure in the tank (like w. an oil pressure relief valve, or some radiator caps)?
You may have to replace the Rochester valve located just in front of your front drivers side tire. Next to the charcoal canister.
Either that, or your evap flange isnât working right, which is rare.
Or the tubes exhausting the pressure from your tank is blocked. A ruptured fuel tank is in your future if you donât relieve the pressure from building up.
Timeisrelative
(Jason Miller 1993 XJS 4.0 convertible, 1997 XK8 coupe )
4
I had this on my xk8. Yes if the rochester valve is clogged it will build pressure in the tank and blow out when you open it. I did a little write up on my xk8 post on how to clean it
Mine also had negative pressure, although not too bad because i never let tank get below half, plus i relieved pressure several times by removing cap.
A simple new Rochester valve fixed it for me. $40 GM part if I recall. On my 88 it was under driver side wheel well, about a one hour job counting jacking, wheel removal, etc. Not sure where yours is on your carâŚ
Until you fix it, i would simply remove/replace cap after every drive.
As a side, I believe there was a TSB to simply drill out the innards of the Rochester valve. Iâve been doing this for years, and it works a treat.
If you really want to go OCD, you can cut open your charcoal canister and refresh the media. Iâve found doing both, effectively eliminates tank pressure (of course), but just as nice, makes any fuel smells in the boot or around thereof, completely go away (until the next time your fuel pump pukesđ).
Funny thing is that, ever since I left my fuel cap loose, Iâm getting MPGs like I never have before (assuming the trip computer is calculating it correctly) ⌠well into the 15s (city only driving). Before it was usually in the 14s, but the last few weeks more like 13s and even 12s ⌠Also, the mechanical odometer and trip computer odometer are closer together in their #s - recently they had been as much as 10% off from each other (which I would think impossible, assuming the computer odometer gets its distance readings from the mechanical odometer ?). For example, if the mechanical odometer showed I had traveled 40 miles, the trip computer might show 45 miles instead.
Whatâs the best way to open up that charcoal canister? I used a Dremel on one once and really made a mess? There is probably a better way?
I never really considered just defeating the Rochester Valve. Probably not a terrible ideaâŚjust cap off the little vacuum line and just connect the two remaining hoses together.
I wouldnât put a hole in canister or Rochester valve. I tried something like that, letting canister breath to atmosphere, but i would sometimes get a nice whiff of gas fumes while driving.
Youâre actually not letting it vent to atmosphere, youâre just creating a clear path for the pressure to move between the tank and charcoal canister. You donât want to puncture the canister.
Youâll find it stops any and all fumes as there is no longer a pressurized constriction in the mix.
Drilling the hole works great / no fumage will occur - as I said, Jaguar put out a TSB instructing dealers to do the same.
As for rebuilding the canister, you can carefully take an xacto knife around the lidâs edge (see pics), and donât worry if you break off bits of the lid along the edges, but donât break the lid across the top.
Clean everything out really good (including getting the strainers completely clean), pitch the old media of course, add new, and then superglue or the like, the lid back on, and everything is new, being absorbed and pressure build up free!
And no those arenât bagels, theyâre fancy dog food samples I got from the groomer. They do look rather tasty although
Thanks, Timer ⌠btw, re: that one poster, is he saying you can access it just by removing the air cleaner assembly, or that doing so just makes the job a bit easier?
Timeisrelative
(Jason Miller 1993 XJS 4.0 convertible, 1997 XK8 coupe )
19
Not sure about that at all if its behind the wheel liner lol. I havenât had to do it on the xjs yet myself though. So who knows
I had the same problem with my 1996. The Rochester valves are NLA so I looked for the GM valve that has been mentioned in another forum and found that it is NLA also. I found that the original valve simply will come apart and is easy to fix. There are little holes that get clogged and they were easy to clean out. I put the valve back together and the problem was solved.
(if that makes a difference)
).
btw, re: that one poster, is he saying you can access it just by removing the air cleaner assembly, or that doing so just makes the job a bit easier? 
