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Gas tank overpressurization

ljobbins

NAXJA Forum User
NAXJA Member
Location
SD County
Today I drove quite a long ways but the last 50 miles was up a mountain from sea level to about 6000 ft. I did not drive fast or really hard. It’s kind of a gradual incline obviously since it takes 50 miles to go 6000 ft. But anyways at the top I noticed a lacking of power followed by a really loud fuel pump followed by a severe gas smell. I pulled over with the car still running opened my door and immediately saw fuel pouring out of the fuel door. I turned off the car and opened the fuel door and there was a crazy amount of pressure from the fumes blowing past the cap. I opened the cap and it sounded and felt like opening the drain plug on an air compressor. It hissed out fumes for about a minute and I felt the tank and it was hot and sounded like it was boiling. I could also hear air coming from the vents on top of the tank so they aren’t completely closed. This is the first time I have had this happen. I was scared that the tank was close to a dangerous level of pressure with gas fumes inside. The tank was about half full when it happened.

So any ideas on what caused it? Is it a random ok thing? Should I look for a clog in the return line? Because of the loud pump, could it have somehow started pumping too hard and created too much pressure too fast for normal relief? Or...?
 
What year? There are several possibilities based on that needed info!
 
88 with the 4 hole fuel injectors swapped. Ax15, all of cruisers tips done minus swapping heads, ALL electrical wiring redone and replaced last year. No other performance mods or anything to the engine. Thanks
 
vent clogged? pretty good elevation change
 
So any ideas on what caused it? Is it a random ok thing? Should I look for a clog in the return line? Because of the loud pump, could it have somehow started pumping too hard and created too much pressure too fast for normal relief? Or...?

The loud pump is caused by cavitation. I have noticed the same while driving a few thousand feet elevation higher than where I purchased fuel. Most of the phenomenon you describe are related to the fuel blend your local gas station sells.

The answer I don't have is why your gas cap vented to atmosphere.
 
Gas cap vents because it probably was replaced. The vents to the canisters could be plugged but it sounds more like your pump is going out and got really hot, to the point of boiling the gas. That kind of heat and thermal expansion will cause a lot of pressure that will easily overwhelm an evap system. First thing I'd do is pull that pump and inspect it.
 
How would I test it? I mean obviously it works to some extent, but what am I looking for or whatnot? I think i'll drop the tank and check the vents and blow air through the line to make sure its not clogged as well. If i'm going to replace the fuel pump, is there a recommended brand? Thanks guys.
 
The beauty of the xj is that you don't have to drop the tank for a pump change. The pressure, return, electrical and evap all are on the cap which is right at the front of the tank. Look for any lines pinched or cracked. Also check the hard lines. Change you're filter too. A plugged filter can make your pump work really hard.
 
Well the anti spill vent caps are on the top so that is why I would drop the tank. And also not sure what I would look for on the pump to see if it's bad?
 
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