Problem with gas cap

[chiefmiller]

I've got a 1966 Dodge Charger 383 4-speed car. I've installed two new vented fuel caps from Stant. I live in Arizona were the temps get up in the 100. So the car been stalling after a short drive. I remove the cap and I have a great deal of pressure in the tank. What the fix?? Chief

[Tilar]

Does it run alright once you open the gas cap?

[68X426]

Hey Chief, welcome aboard. I have no specific advice on the pressure and its possible relation to stalling, except to relate personal experience.

My location gets into the 100s all summer (but certainly not like AZ). My gas cap is always pressurized, even more so on the hottest days (even on cold days in winter). It's a Road Runner, but is that so different than a 66 Charger system?

There is no stalling issue with my pressure situation. So I would just wonder if the stalling is not connected to the gas cap and caused by other issues (carb, fuel pump, or ?).

[chiefmiller]

It runs fine once I relieve the pressure off the tank. I do mean it's a lot of pressure. I check the cap to see if it's working on the cap itself and the relief valve is working fine. Not sure what's going on.

[Tilar]

If there is that much pressure on the tank that it stalls out, then it must be flooding through the carb. A possible solution is to try a different brand of fuel cap or install a pressure regulator that limits the pressure to the carb. You can buy one that you can set to 5ish pounds.

[ODZKing]

I have a 67 and on the way down to Carlisle this year on Thursday, tempuratures were in the 90's and one bank sign even said 102.  About half way, we stopped for fuel and in removing the fuel cap, "whoosh".  It is an original cap and does not do it normally but it did that day.  I'm told after asking numerous people it is fairly normal to have some pressure but not enough to blow it off into your hand.
I had no issueson the trip but that fact that you relieve the pressure and it runs is suspect.  Do you immediately start it or does it sit for a while? Is it possible the small bit of fuel line from the sender is cracked and it is trying to suck air as well?

[chiefmiller]

It only happens when it gets hot (at least 95 degrees or more). It still runs, but it wants to stall at higher rpms. So I just back off the throttle. The car never stalls out or quits on me, but acts if no fuel is getting to the carb. Now I've replaced the fuel pump and fuel filter. On another note the car does not stall at any time when its cool outside if you call cool under 85 degrees. Chief

[Tilar]

If that's the case, it sounds more like a vapor lock issue to me.

[chiefmiller]

I agree, but how to I fix it? I thought the cap would take care of that.

[resq302]

Vapor lock could be cuased by numerous things.  First, I would check the fuel line and how it runs inside the engine compartment.  We had a problem with our 70 el camino SS 396 like this and it turned out that the line that we got from the repro line company was actually the incorrect year.  Once we got the correct routed line, our vapor lock issues went away.  All this transpired back in 2006 when we were invited out to the Eastern Concours d'Elegance show with the elky.  It was over 100* there that day and had to do a parade of the cars where they stop each car on the red carpet and talk about the car.  Once that we done, we ended up winning and having to go through that parade again.  After that was all said and done, we loaded the car up onto the trailer and headed home an hour and a half away.  Once we got home, the car would not start.  Pushed the car out of the trailer and let it sit overnight only to have it fire right up the next day.  Simple stupid things are always the hardest to fix it seems.

Also, like someone else said, if you have a minor crack in the rubber line by the sending unit, you could be sucking air which could also cause the problem you aer describing, especially at higher rpms when you are flowing more fuel.

[chiefmiller]

Thanks for the information. I'll check on both.

[Tilar]

Want an old time fix for vapor locking to test this? Take 3 clothes pins and fasten them to the fuel line between the fuel pump and the carb.



Now to explain this, The clothes pins will absorb and disipate the heat from the fuel line which will stop the fuel from boiling which is what a vapor lock is. Fuel boiling inside the carb or the fuel lines.