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Discussion Starter · #1 ·
Today I coasted down my hill into my driveway and my trooper (89 4ZE1 MUA5) died just before I parked. After that it cranked but wouldn’t start. I didn’t notice anything obviously wrong under the hood so I thought I’d remove the gas cap and try to start it. There was more pressure released when I opened the gas cap than i normally observe (I had half a tank if it’s relevant). With the gas cap off the car started right up.

Any ideas what caused this and what might be wrong?

Also noticed my rad is leaking… great.

Thanks

Mike
 

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Discussion Starter · #4 ·
Thanks for the info. that makes a lot more sense. Is there something that would have caused that? Anything I can check?

mike
 

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Gas cap shouldn't really have an effect on this. (if the system is working properly) That is supposed to be a closed system. The cap should be sealed and the system should "vent" through the charcoal cannister. When parked, the cannister is supposed to collect any vapors. on starting, a valve should open causing the vapors to be sucked into the intake and be burned. Somehow, at that point, the tank is also vented through the cannister. You might want to double check all the hoses going to the cannister for correct routing. Dennis
P.S. I have seen some systems where there IS pressure when the fuel cap is cracked open.https://www.carparts.com/blog/what-does-a-vapor-canister-do/
 
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could have over filled the tank or got fuel in the vapor line, getting to the canister, clogging it. not common, but does happen. Also the cap is suppose to vent when pressure gets too high but again, the vapor is suppose to go through the vapor canister FIRST...then the cap will release pressure if it gets that high...vacuum, cap wont vent, nor will the canister......as Dsuzu said, check the lines and even pull them off and remove the charcoal canister, see if it has fuel in it or the lines are wet inside.
 

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as mentioned,. the tank has to vent to allow air in as fuel level decreases. if not, picture a full tank (this little air volume) with fuel level dropping as it's consumed. pressure is inversely related to volume, so as fuel decreases the area between gas and top of tank increases.....but because there is no vent allowing air in to equalize pressure with ambient air pressure, the air pressure in tank decreases to a point of a vaccum. So there is a tug of war between fuel pump suction pressure and gas tank pressure, eventually as gas level decreases the pump can not overcome negative pressure in tank and there is no flow to engine.

modern emissions include a sealed gas cap and valve to equalize pressure in tank to reduce what's called evaporative emissions (prevents gas from evaporaing into atmosphere). All you need to do is drill small hole in cap (not legal) or check vent line for clog or electrical valve which is likely failed in closed position.

good luck, may the force be with you
 

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Yup, as has already been stated, sounds like the system is clogged somewhere. Might need to drop your fuel tank to check the valves and such o_O:unsure:
 
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