Questions and Answers
Gas Cap Strangeness
Q. Hi Vince, Here goes... today is September 6th, my truck ran great today and ran great yesterday but the day before and the day before that is was jumping like it was missing a spark plug but just for three miles or so then it stops and runs well for the rest of the thirty mile trip.
I have been documenting this for awhile and three months or so. Here is the strange thing is that every time I fill the tank up with gasoline at night always the next morning here we go again with that [missing/vacuum thing] for three miles again and then stops. Now the service engine soon light came on. I remember that the same light came on when I left the gas cap off. Then I put the gas cap on and three days it went off. So I took the gas cap off last night and there was this air that came out. Well this afternoon on the way home the service engine light went off. I was so happy!! Is that strange or what?
1997 Nissan truck, 4 cylinder, 65,000 miles.
A. Not so strange, the Evaporative Emissions System (EVAP) is part of the EFI system and as such is monitored by the ECU.
The evaporative emission system is used to reduce hydrocarbons emitted into the atmosphere from the fuel system. This reduction of hydrocarbons is accomplished by activated charcoal in the EVAP canister.
The fuel vapor in the sealed fuel tank is led into the EVAP canister which contains activated carbon and the vapor is stored there when the engine is not operating. The vapor in the EVAP canister is purged by the air through the purge line to the intake manifold when the engine is operating. EVAP canister purge volume control valve is controlled by engine control module. When the engine operates, the flow rate of vapor controlled by EVAP canister purge volume control valve is proportionally regulated as the air flow increases.
EVAP canister purge control valve shuts off the vapor purge line during decelerating and idling and under normal operating conditions the valve is usually open. EVAP shut valve shuts off the vapor charge line when fuel is being supplied to the fuel tank.
Since the Check Engine light came on, I would have the DTCs pulled from the computer and see what caused the light to come on.
Additional Information provided courtesy of ALLDATA