Retaining EVAP on a 96/97 LS swap

[0xDEADBEEF]

Ok, i guess its better than having no EVAP at all. But it's probably better if i can find a way for it to work with the electronics that I have, preferably without swapping in a 98 tank and adding sensors. How does yours work? Are all of the sensors and connections just in place to look good for the inspection guy, but none of them actually work since you deleted it from the PCM? (even though they could work if signaled to).

It's just for appearances. It would work if the PCM tells it to, but I don't think it ever does. The inspectors in my state have no way to test it and it doesn't smell of gasoline or having fueling issues, so I never went beyond that.

 

[slow_c1500]

Wouldn't the emission readiness on the scanner say "not ready" since you tuned the EVAP out of the PCM (or maybe your state is only visual inspection)? And you have no issues with pressure building up inside the gas tank?

 

[0xDEADBEEF]

Wouldn't the emission readiness on the scanner say "not ready" since you tuned the EVAP out of the PCM (or maybe your state is only visual inspection)? And you have no issues with pressure building up inside the gas tank?

I turned off the MIL in the tune, but the actual logic in the PCM is still there. I don't recall if the inspector actually plugged into the OBD2 port. We only had to worry about it that one year and then it hit 25 years old and was exempt after that.

You could wire in a resistor to fake a nominal reading, but I think in the time to do that you could have just as easily have added the pressure sensor. It doesn't have to be in the tank. You could put it inline to the evap canister.

 

[slow_c1500]

I guess adding the pressure sensor wouldn't be too annoying then, if it doesn't have to be in the tank. Don't the LS harnesses also have a fuel level sensor that it needs for the EVAP, or it this sensor for something else, and I wouldn't need to add it?

 

[0xDEADBEEF]

I guess adding the pressure sensor wouldn't be too annoying then, if it doesn't have to be in the tank. Don't the LS harnesses also have a fuel level sensor that it needs for the EVAP, or it this sensor for something else, and I wouldn't need to add it?

I don't know, it could just be for the gauge. You could possibly split the signal off your tank's sensor so the PCM can see it and the gauge can still work, assuming they aren't opposite.

 

[slow_c1500]

I think your right, it's just to feed the NBS gauge. For 96-97, the sender wire goes straight from the fuel tank to the gauge, so I wouldn't need to add that sensor or really do anything. I think to make the EVAP fully functional, I need to swap to a 98 or newer canister since the 96-97 canister doesn't have a place for the extra connections. As well as adding the tank pressure sensor.

 

[L31MaxExpress]

Purge solenoid is the only part you need. It will start purging the canister as soon as the PCM goes into closed loop.

That is unless you are in CA, then it is better to just put the stock engine back in your truck and buy a vehicle with the powertrain you want. A 4.8L or 5.3L is a step backwards from the 5.7L when they have to stay stock anyway and run on the stock tune. Change 1 parameter in that LS PCM and you will fail smog in CA's referee process.

 

[slow_c1500]

With all due respect to the small block, the vortec injection system sucks donkey balls and I want to get away from it as soon as my truck needs a new motor. Also there's not gonna be any distributor problems on LS engines so I see this as an absolute win.

Thanks for the info about the purge solenoid though. So would I just delete the other unused EVAP-related functions (tank pressure, vent valve) from the PCM along with VATS? (I am relocating states or registering in south dakota, i am not concerned about the requirements)

 

[L31MaxExpress]

With all due respect to the small block, the vortec injection system sucks donkey balls and I want to get away from it as soon as my truck needs a new motor. Also there's not gonna be any distributor problems on LS engines so I see this as an absolute win.

Thanks for the info about the purge solenoid though. So would I just delete the other unused EVAP-related functions (tank pressure, vent valve) from the PCM along with VATS? (I am relocating states or registering in south dakota, i am not concerned about the requirements)

That is the way to make the PCM work. In a swap environment "pre 1973" delete everything not used.

 

[slow_c1500]

Awesome. Just out of curiosity, what exactly does the other EVAP connection do? (I believe it is called the vent valve), and why isn't it needed?