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Fuel Pressure Issue

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Fuel Pressure Issue
flyer92

flyer92

Jeeper
Posts
40
Thanks
2
Location
California
Vehicle(s)
'80 CJ-5, 258, T176, D300, AMC20, D30
My 1980 CJ5 has been running fine without a charcoal canister for over 15 years, and the vent line simply terminates with a plastic vent cap as shown in the photo below. I recently noticed that fuel now leaks out of the vent cap, even after a short drive. Since the venting system is pretty simple, I thought I might have a faulty rollover check valve, so I replaced that with a new OEM valve (yes, they are available...same part is used on Deloreans!). Unfortunately, the problem persists, so I suspect the only other thing that could affect it is the fuel filler cap. I use the correct vented/locking cap (Stant #10592), and mine is only 2 years old, so I'm not convinced this is the source of the problem either. The cap seems to be working properly. I am very uncomfortable driving with a fuel leak under the hood, so greatly appreciate any info/advice on what else I can investigate. Many thanks!

IMG_4491a.webp
 
I have been tinkering around with the fuel tank vent system for the past 25 years or so. Having made various changes to try and simplify with poor results. I installed the DeLorean rollover check valve to replace the oem version also, even going as far as having one for each of the fuel tank vent lines. I am finally back to the complete oem vent system which seems to work best. I think that the oem liquid check valve is the critical item in that system. Fuel tank venting is pretty critical for me as I have throttle body injection with an external fuel pump.
 
Thanks, Torx. To be clear, what other components are installed in the venting system, other than the check valve?
 
Well for starters, a fuel tank vent system layout will be in a fsm or most repair manuals, even online. I think that the charcoal cannister would be better bet than what you have pictured. Going up the line is the rollover check valve, like what you already have. I am pretty sure that it is a back up to the liquid check valve. The LCV has two hose inlets for the fuel tank vent tubes and an outlet to the rollover check valve. I have filled up my charcoal cannister with gas a couple of times during a few of my vent system "modifications". With the oem setup, I did tip my CJ on its side and found out that it works quite well. With a few helping hands, I was able to put the dirty side down and it fired right up.

Edit: The LCV and rollover check valve are located next to each other up underneath the left rear quarter panel. Where they work best.
 
Are you sure it's not coming from the fuel filter?
May I ask-how do you get that SMOG'D every 2 yrs, with that setup? :confused:

LG
 
Lumpy...luckily, my vehicle is registered in Florida, where we don't have emissions inspections. If that were the case, my CJ would fail miserably!

Thanks, Torx. I am familiar with the fuel system layout, and have the requisite schematics/manuals. Was just curious what you have in your specific configuration, so apologies if i wasn't clear on that.

Unfortunately, I can't find a new LCV, and the used ones I got from a local junkyard and JW's were brittle, cracking, and not very reliable. If you or anyone else have an idea on where I can find something suitable, I'm all ears!
 
Or these folks should have what your looking for too: mtscompany.com
I haven't ordered from them yet but will when I start working on my fuel system.
 
Thanks for the great recommendations! After scrounging around in my old parts box (don't we all have one?), I realized that I had purchased a valve from George's Jeep that was supposed to be a replacement for the rollover check valve. I never really used it because it is a bit chintzy, but I found several internet references that claimed it could be used as the LCV. In fact, some sites even advertised it as an LCV replacement instead of a replacement for the rollover check valve. Since I'm without an OEM style LCV, I figured it was worth a shot and it seems to be working OK (see photo). Of course, there's no knowing if the valve is merely serving as an another reservoir where gas can collect, or if it is really working like it's supposed to. I guess only time will tell, but it at least serves as an interim fix until I can find a good OEM style LCV. Will advise if/when I can find one, and appreciate all the help!

IMG_4493a.webp
 
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Thanks, Torx. I think I will keep that setup in my back pocket as a last resort, as I'd prefer to keep it simple and stick with an original configuration (or as close to it as I can get). Looks like the aftermarket LCV I had in my last pic is the same thing that MTS is selling, so perhaps that solved the problem.

Although not installed, I actually have the original charcoal canister, but I'm sure it needs new innards. That may be my next project, but need to solve the valve issue first, or I'll risk having fuel drip inside a newly-refreshed canister. Ugh...the horror never ends!
 
As expected, Willysworks didn't have the LCV in stock and directed me to MTS. Although I already have the valve they are selling, I called them anyway and learned that the valve is intended to replace both the LCV and RCV. Unfortunately, that valve alone just didn't work out, which is why I am now using it along with an OEM RCV, per my last photo. All seems to be OK for the moment, but there's no knowing if the valves are working as intended, or just serving as a place for fuel to collect. Will continue to monitor this before adding the charcoal canister to the mix, and will also need to refresh the internals on that too. I'd appreciate any advice or links on that project, as I'm sure many of you have already done it. Thanks in advance, and will keep you posted on how this valve config works out.
 
Looking at YouTube, there seems to be a lot of postings on rebuilding them. I am sure those valves are designed just to let the gas fumes through and not the liquid gas which can happen if not set up right. Then the charcoal takes over, on my oem cannister, there is a vacuum port that does draw the fumes into it also. I once sent my cannister to a guy who rebuilds them. The smog guy I go to says the oem cannister is required, although he has passed me using an aftermarket one.
 
Thanks, Torx. Agree that the valves should only be allowing gas fumes thru at a specific PSI, but I'm not certain that they aren't just collecting liquid gas. Each valve by themselves let liquid thru, so who's to say that using both of them in series is really any better? Good to know that the original canister is required too. I once (foolishly) considered selling mine on eBay, but so glad I held onto it, even though it is serving as a paperweight right now!
 
Another thing is that they should be mounted as high as possible underneath that left rear quarter panel. So that gravity can help keep the liquid fuel out of the valves.
 
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