jahajazz

iTrader: (2)

For the LS-series EVAP system, I am attempting to figure out exactly what the PCM needs to maintain functionality.

Physically, I know there are three components to the system:
The Vapor Canister, connected to the fuel tank and containing fuel evaportated vapor from the tank.
The Purge Valve Solenoid, which allows fuel vapor from the canister into the manifold when commanded by the PCM.
The Vent Valve Solenoid, which allows air back into the canister when commanded by the PCM.

My question comes in regards to what signals the PCM needs to operate the system.

I know there is a pressure sensor which can be retrofit in the vent line from the tank.
There are also other sensors which are used to determine when the valves are actuated.
Some of these are the throttle position sensor, the engine tempurature sensor, and the vehicle speed.

Is the fuel tank level required for the system to operate? Or more specifically, for those who have sucessfuly adapted this system, did you wire the fuel level sensor to the PCM?

Thanks for any information you can provide,
Jahajazz

flame

iTrader: (13)

If all you need is to be able to purge the vapours then just hook your original vent line from the canister to the purge solenoid and you're done. The rest of the parts are only required when the pcm performs the leak test on the fuel system. The vent solenoid is normally open and only closes for the test. You would require the fuel level sensor, tank pressure, vent solenoid, purge for that to function.

jahajazz

iTrader: (2)

My goal is to have the system function in terms of purging vapors, I do not really care about the self test functionality. I know the fuel tank pressure sensor can be tuned out, does that mean the PCM will not attemp any of the self test funtionality if this sensor is removed from the tune?

flame

iTrader: (13)

Hasn't caused me any problems in the three summers of driving my swap

jonathan_ed3

iTrader: (4)

I know this is an old thread, but it specifically applies to what I'm wanting to do.

I want to use my existing evap cannister, hook it to the LS1 purge solenoid, and purge the fuel vapors using the LS1 PCM to do so.

What specifically needs to happen in regards to the PCM tuning to turn off the self diagnostic procedure, but maintain the purge functionality of the solenoid?

The purge solenoid is normally CLOSED and OPENS via the PCM. So obviously it still needs PCM control to function properly.

Can anybody share insight on this?

69 Ghost

Fuel level sensor needs to be wired to the PCM

Russ K

iTrader: (1)

The purge valve will function properly once the the PCM is in closed loop. The vent valve & fuel tank pressure sensor are only used to test for a vapor leak (loose gas cap). Then just disable the evap vent, fuel tank pressure sensor & evap leak codes in the PCM.

Did this on a 1968 Chevelle LS3 swap, works great.

Russ Kemp

jonathan_ed3

iTrader: (4)

Thanks for contributing to this thread.

I want to make sure I'm digesting this properly.

So you're saying you can tune out the evap vent, fuel pressure sensor, and evap from the PCM, but it will still control the actual purge solenoid on the intake manifold?

Under what conditions is the purge solenoid commanded to open if you delete the other functions in the PCM?

jonathan_ed3

iTrader: (4)

And do you have an actual evap canister in your car? Or is it just a vent line from the gas tank?

Russ K

iTrader: (1)

Yes.

The evap purge valve stays closed until the the PCM enters closed loop. That's when the fuel trims are active.

Russ Kemp

Russ K

iTrader: (1)

Yes, I mounted a canister from a 1997 Tahoe under the hood & used the stock 5/16" fuel line for a vent line from the tank to the canister.

Russ Kemp

jonathan_ed3

iTrader: (4)

This may be something I need to do more research on, but do the additional valves on the actual canister itself contribute to successful evacuation of fuel vapors?

Or is everything aside from the purge solenoid on the intake manifold and the canister merely for leak testing?

So for this to function in the way you describe, the charcoal canister itself is always "open", in that it always has a supply of fuel vapors pushed to the purge solenoid.

Then the PCM commands the purge solenoid open, which allows the vapors to be sucked into the motor and burned off.

There's no valves on the actual canister that also need to open in conjunction with the purge solenoid itself, aside from those necessary for the PCM to perform its self testing?

jonathan_ed3

iTrader: (4)

What role does the evap vent valve play in this overall function? Doesn't it need to be commanded open and closed via the PCM in conjunction with the purge solenoid for proper total system operation?

Russ K

iTrader: (1)

The vent valve only closes when the evap leak test is run. It's not used for the actual operation of the evap system.

Russ Kemp

Russ K

iTrader: (1)

There are no additional valves. Only the purge valve draws the fuel vapors from the canister once the engine is in closed loop fueling.

Correct

The canister stores the fuel vapors until the engine is in closed loop fueling.
Then the pcm opens the purge valve to draw the fuel vapors into the intake manifold.

Correct

Correct

jonathan_ed3

iTrader: (4)

Russ, thank you for all the posting. I apologize if I'm being dense, but I want to make sure I understand all of this. If I can get mine to work like yours, it'll be extremely easy. All I'll have to do is wire up my purge solenoid and then perform the necessary PCM functions you described.

Does the PCM not need input from the fuel tank pressure sender, the throttle position, and the speed sensor to calculate how much flow to provide at the purge solenoid?

If it doesn't have this info, how does it know when, and to what extend to purge the canister?

What happens if the purge solenoid opens under WOT? What does closed loop fueling mean?

Do you know under what conditions your particular setup is purging and how often?