ls1nova71

iTrader: (4)

Does anybody know for sure how the purge solenoid works? Until recently I was under the impression that the fuel tank pressure sensor needed to be hooked up, but now I'm not sure. Will the purge solenoid work by it's self? And if so, how do you hook it to the charcoal canister? The canister i have has 3 ports on it, one says 'fuel tank', pretty straight forward, the line it was hooked to goes to the tank, the other two say 'PCV' and 'carb'. The one labled 'carb' I'm thinking would be the one that would go to the purge solenoid. The 'PCV' one, was originally T'd into the PCV hose that went to the carb and valve cover mounted PCV valve. Should I T it into the line going from the fitting right behind the throttle body to the right valve cover? It seems to me it would just make a big vacuum leak. Or I was thinking I could drill a hole in either the air cleaner box or the air intake going to the throttle body, but not sure since it would be after the MAF if that would be a good idea. Anybody have any thoughts?

ls1nova71

iTrader: (4)

Nobody has done this?

mantycarguy

The factory evap system works as such. The purge sol/valve was hooked up to a port on the left side of the throttle body behind the throttle blades which provided a constant vacumn to the valve. As hot fuel returned to the tank the pressure in this closed system would rise, causing the fuel tank pressure sensor to tell the pcm to activate the purge valve. Vacumn then pulled these vapors into the engine to be reburned. A vent valve on the other end of the system would also allow fresh air in during this process. The idea was to maintain a neutral condition/ 0psi per say. All vapors were routed to a carbon canister to separate any liquid fuel from being drawn into the engine. Furthermore the system does its own monitoring via the form of EVAP. During these tests The purge valve is opened and the vent valve is closed thus pulling a vacumn of approx. 15 inches. The pcm monitors this vac. for a predetermined period of time to see if it can maintain this reading through the fuel tank sensor. Once it passes the test, normal function can resume. If it fails, check engine light is illuminated and no further tests are run. Normal purge and vent valve operation still remain functional. In conclusion, without a fuel tank pressure sensor there is no way for the pcm to know when to purge the system of excess vapors.

flame

iTrader: (13)

The tank pressure sensor is only used for the evap leak test. The purge works fine without it. Plug the port on the can that was pcv and hook the carb port to the purge solenoid and from there to the intake.

mantycarguy

Flame I agree for the most part except in the event of a stuck purge valve the pcm uses this information to open the vent valve to prevent the tank from collapsing.

ls1nova71

iTrader: (4)

So if it will remain functional, it would work? Does it rely on any other sensors? I would think it would. Or does the PCM just purge it at randomly set intervals?

mantycarguy

It primarily relies on quite a few different sensors for operation along with run time. As flame says It will probably function ok without the fuel tank sensor. You just wont have the extra safety measure in event of stuck open purge valve You would need to have a vented gas cap to allow air in also.

ls1nova71

iTrader: (4)

I think I'll just give it a shot. Pretty sure I have a vented gas cap just by design of them never sealing very well! No way I could put the pressure sensor in it and have it work because of that cap anyway, not to mention I don't have a vent valve or a place to put one.

garys 68

iTrader: (1)

Do a google of GM evap controls and go for the tech pdfs.
Just reread your post, you're using a charcoal canster for a carb. It has an inlet for fumes from the carb bowl. That would be the carb port, cap it. Guessing the air inlet on yours is on the bottom.
The pcv line did T into the pcv line or attached to the valve. It is line to hook up to the purge solenoid.

flame

iTrader: (13)

The vent valve is on the fresh air side of the canister and is a normaly open solenoid. The only time it closes is to do the evap leak test.

ls1nova71

iTrader: (4)

Ok, another question. What would happen if I just 'T'd it into the hose that goes from just behind the throttle body to the right valve cover? If i just cap the small line that went to the carb, hook the PCV hose up like I'm thinking, and the line to the tank will it vent the tank right? That's prertty much the way it was originally. i was working on a truck at work last night and noticed it was set up this way, no purge solenoid, just vacuum off the intake. It was a 1990 2.5 S-10 set up.

garys 68

iTrader: (1)

One function of the purge solenoid is to only open when the engine can compensate for the vacuum leak or additionalfuel caused by air flowing through the canister (closed loop). I think it also uses pwm to control the amount.