Howdy fellow Cat enthusiasts. Barely warmed up this evening and it stopped running. Fuel filter was empty and would not start. Waiting on a tow, after about 2 hours (nice country road thankfully), it started to rain. Figured i try again and she ran fine the two miles home. When i started it before the quick cruise, i heard a new sound from the tank, almost a faint bang. When it stalled, i heard gas pouring back into tank. It has never vapor locked. There was some debris in filter but not much. Ordered new pump while i was waiting. Crossing off the easys first but reaching out to the crew for any advice…
Sounds like the gas tank is not venting. Fuel pump pulls fuel out and air cannot replace the fuel. Finally you get so much vacuum in the tank that the pump can’t pull fuel out, and the tank sucks the fuel back into the tank when engine dies.
You didn’t mention what year, but 70 without CA emissions, and earlier cars need a vented gas cap to let air into the tank to prevent this. CA emissions cars have a valve above the rear axle that lets air into the tank to prevent this, but vents any positive pressure air in the tank after shut off into the charcoal canister under the engine.
Thank you. Its a 1970 with Cali emissions albiet new tank. When its low on gas, there is a significant amount of air pressure coming out when the cap is taken off. Perhaps related is that yesterday the gas gauge was past full which was a first (i didn’t overfill). Thanks again,
Paul
So there is your problem! The lid for your CA emissions tank was not vented. Now that you replaced the tank, you need to change to a vented cap.
I am adding to what Calicat correctly said - the California emission system vents the gas tank through a charcoal cannister so the gas cap is not vented. When you changed to the new tank the gas tank has no vent. It needs one!
Ok, will get one. I love this forum! The only potential problem to closing this caper is that I have been driving it for a few months with no issue. I did mod the cali filler neck for a proper fit so prior to that air (and gas) had an out but that was months ago. Of course, it is only the analytic mind required of the classic Cougar owner that prompts this after thought.
Thanks all!
The lack of a vent probably became more of a problem when you filled your tank. Less air in the tank to suck out, so you would get more of a vacuum quicker.
I went through this same process on my 70 with CA emissions. I replaced the filler neck with a non-emissions one so I could use a standard vented cap.
That makes sense, tank is likely the fullest its been. I could not find non-emissions filler neck. So i gather a vented cap for a 70 Cougar will not fit, i was hoping the cap specs were the same for Cali and “49 state” filler necks.
Paul
Unfortunately, no. The emissions filler inlet and non-vented cap are smaller diameter.
Options then are to find filler neck, vent a cap myself, never fill up. Thanks!
Years ago i had a similar issue…a 1/16 hole drilled thru the center rivit of the cap solved the issue
Sounds good. Local auto store had cali emissions caps…which is odd but they probably fit a host of other Fords.
Looks like the right one is available: Fuel Filler
Mine is a 70, will it work?
No, but I do see aftermarket ones for 70 Mustang out there.
Anybody know if Mustang and Cougar filler necks are interchangeable?
I drilled original cap, took it out for a pensive cruise and no issues.
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I’ve got a 68 302 with 4BBL holly carb…vented gas cap….recently it seems like I get A LOT of pressure escaping from the cap when I remove cap. Do vented caps get “clogged” over time or does the spring ever malfunction somehow?//
That’s how the vent works. It allows air in but not out. In summer you get a lot of expansion as fuel picks up heat from the road
Thanks….i have seen a tad of gas around the crimp of the gas pump (mechanical) that I read could be from the “weep hole” lf there was a hole in the pump diaphragm ….otherwise car starts, runs, accelerates and purrs like a kitten so I’m having a hard time believing it’s the pump itself🤷‍♂️
No you need a different one that is out of stock at WCCC.