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Evap canister & Purge control valve

11-29-2006, 06:15 PM
Hi, and thank you to everyone reading this post.
I recently had my 1998 Altima diagnosed by a dealer because "service engine" light was on. They told me that I need to replace evap canister and purge control valve (i believe they are both related to emission control system). I understand that the evap canister prevents evaporation of volatile organic compounds from being released into the atmosphere and that the purge control valve controls the feeding of this evaporated material back into the engine. I tried to research on the effect of this problem to the car (ie. if I do not fix it) and potential damages, but only thing mentioned was that the gas mileage will drop due to evaporated fuel? Does anyone know what may happen to the car if I do not fix the problem (besides passing emissions and low mileage). I plan to get this repaired soon, but does defective evap canister and purge control valve present potential serious damage to the car/engine if not repaired right away? Should I not be driving the car until I repair the problem?
Thank you in advance for all replies and comments.

11-30-2006, 09:16 AM
This was the information I found...

The evaporative emission control system is designed to prevent the escape of fuel vapors from the fuel tank and fuel system into the atmosphere. Components include a charcoal-filled vapor canister (to store the fuel vapors), a purge valve (for routing the vapors back to the engine) and various vapor hose connections.

The evaporative emission control system requires no maintenance and seldom causes problems. But if the purge control valve leaks, it can create a rich fuel condition that increases carbon monoxide emissions, causes surging and causes poor idle. Air leaks in the purge-control valve vacuum plumbing have a leaning effect on the fuel mixture and can cause lean misfire, idle problems and elevated hydrocarbon emissions."

11-30-2006, 12:05 PM
i'm assuming they told you that you needed both because the charcoal in the canister had broken loose and been sucked up to the purge valve? if thats the case, then yes, you need both. the charcoal will clog the valve or keep it from closeing completely. if it is stuck open, then yes, you can have a vaccum leak, which can cause idle or other problems. if you're not having any problems, then i would recommend disconnecting the purge valve so it cant operate until you decide to fix it. the check engine light is already on so its not gonna change anything

11-30-2006, 01:15 PM
Thank you for your reply nissandoc.
Does this mean that there are no other possible problem besides idling that could develop from this? Also, I am confused on how disconnecting the purge control valve will change from what it is now. If I physically remove the purge valve, wouldnt the system still have the same problem (ie. vacuum leak you mentioned). Thank you again for your help.

11-30-2006, 01:36 PM
if you disconnect the electrical connection, the ecm wont be able to control the valve(open\close). if you remove it, the hoses will need to be plugged, better to just disconnect the electrical connection. you can remove the canister side hose from the valve and at idle, if you dont have vaccum pulling on the inlet tube, its fully closed. simply disconnect the electrical connector. no more worries until you fix it. but when you do, if you see the charcoal pellets in the hoses. be sure to blow them out with compressed air from front to back with all the hoses disconnected. good luck.

11-30-2006, 07:08 PM
Thank you nissandocfor your suggestion.
So are you saying that these loose charcoals can get pulled into the intake and possibly build up in the engine (since the vapor leads there) or am I just misunderstand?
I guess I will pick up a repair manual and find where the canister and valve is and see if I can disconnect the valve from the ecu as you suggested.

12-01-2006, 07:53 AM
its possible that they will get pulled into the engine. most likely will just get pushed out the other side. never seen any engine damage from this. if you dont find the charcoal pellets in the system then you most likely wont need to replace the canister.

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