i have been having some idle problems but that is fixxed now.... but i just noticed that there was nothing connecting to either of these two, should they connect? i think the one on the firewall comes from the gas tank, and the one on the throttle body is pulling a vacuum.

if it matters, the car is an 89 DX and the engine is a jdm b20.

 

I think the port on the throttle body goes to the charcoal canister.
Then the nipple on the firewall goes from canister to gas tank.

 

no, the fuel return on on the drivers side of the car, over by the break booster.

 

the car runs and i drive it everyday. nothing come out from the nipple in the picture, but some times i smell a gas vapor?

 

The line is the vent for the gas tank, hence the reason for smelling gas. A line runs from there to the charcoal canister like stated above. And from the charcoal canister to the nipple on the throttle body there should be another line. Is your charcoal canister missing?

I have seen people that have removed the canister run a line straight from the gas vent line straight to that nipple on the throttle body. I do not know if it affects mpg or performance running it like this though.

 

no i do not have the charcole canister anymore its long gone. would it be safe tho to just connect the 2?

on my old 90 si, it was the same way but i never smelt gas coming from that line.

 

Cap the throttlebody one and leave the vent on the firewall alone.

 

I connected the 2 when I removed my charcoal cannister. No need to pollute.

 

Do you realize what you are doing?
You are pulling fuel tank fumes into a vacuum port on your throttlebody all the time now.
"No need to pollute", but you remove the EVAP system.
Now you are making your engine run rich most of the time.... "no need to pollute" he says.

EVAP system turns on and off to allow the vapors back into the engine when they can actually be used and burned up properly.

 

Not exactly. That port only sees vacuum when engine is running and when the throttle is partly open, it's a ventury type vacuum port. If you look inside the TB, that port opens up just before the butterfly on the non-vacuum side.

Connect the two or cap the two, and problem solved.

 

" when engine is running and when the throttle is partly open"

Most of the time then, right?
But whatev's though.

 

That's how the EVAP works, it doesn't get constant engine vacuum.

 

I know how it works.
If your solution was really that effective, then they wouldn't have a canister, valve, and solenoid between the throttle body and tank tube.
It's ECU controlled to allow the vapors into the engine, not throttle body vacuum controlled.
When an EVAP purge solenoid fails and sticks open, your engine runs Lean and possibly rough because there is now an uncontrolled vacuum leak to the gas tank. ECU tries to correct for O2 sending lean conditions and you now have an emissions failing engine.

 

He doesn't have a canister. Your point is mute.
OP, just plug the ports and move on with your life. It will be fine.

 

This is getting painful. I'm not arguing for arguments sake.
The best option is to cap the TB and vent the vapor line. I would say plug the line too, but I think that may pressurize the fuel tank - I know that plugging the line somewhere creates pressure, but can't remember where - makes engine run rich.
Running vapor line to TB will give you a lean condition and possibly a rough running engine especially noticable at idle.

Lastly, to beat a dead horse, my point remains and is not moot. Hooking the TB to the vapor line is not an effective way for reducing pollution. Obtaining the proper emissions equipment is the right way to do this.

 

4dr is right again! lol

Don't connect them together. Cap the TB, and put an open vent line on the one in the firewall. You will probably smell fuel vapors occasionally, but unless you want to reinstall the charcoal canister, then you will have to live with that

 

So the only issue, with connecting the nips, is running a little rich? Yeah I will keep them connected unless someone has some has some science that will prove I am destroying my car by connecting them.

By they way, I disconnected them to see if my smooth idle would get smoother. Drove around for a day and nothing changed :shrugs:

I'm going to pull my plugs to check for lean condition.



*edit* pulled plugs, no lean condition indicated by color.

Worst comes to worst I can put the purge solenoid on mid line.

 

Hmm.... Just did some research and it seems that pre1996 jdm motors didn't have evap purge solenoids. So even if I reinstalled my evap purge solenoid I doubt my PW0 ecu would even send a signal to the evap purge valve. Seems as if jdm motors pulled vacuum all the time. Can anyone confirm this?

 

I guess if I wanted to be thorough I could put one of these in between the nipples.

In-Line Air Dryer & Adsorber Filters | AirDryers.com

 

Hondata has confirmed it. Obd0 pin a6 matches up with obd1 pin a20 to add evap purge solenoid when creating obd0 to obd1 conversion harness. According to hondata link below the pw0/pr3 a6 has no function. Therefore the jdm pw0/pr3 ecu does not send a signal to the evap purge valve like the Usdm obd0 ecus. In conclusion, if I would have left my purge valve connected, it would have acted like a plug on the gas tank vent line because the ecu never would have sent the signal to open, thus proving that the jdm motors had vacuum all the time on the vent line.

www.hondata.com/techwiringpw0.html



So why can't you connect the 2 nipples?

 

You can, you absolutely can. The reason you can is because that is VENTURY vacuum not direct engine vacuum, big difference.

That port only sees vacuum ( about 5 in/hg) when the butterfly is open to no more than 5 degrees. Beyond that, vacuum drops out. Also , no vacuum when the throttle is closed and no vacuum when accelerating. So it's the perfect port for sucking fuel vapors into the engine when you are cruising.

This would not work if the port had direct engine vacuum where you get upwards of 20 in/hg of vacuum on a very constant rate.

 

The fumes from the fuel tank normally travel into the charcoal canister and get stored there. These fumes then get drawn out of the canister once the engine is started and up to temp. Once the motor is up to temp, the purge solenoid sends a vacuum signal to the canister (via the #7 hose) that allows the vapors to be slowly drawn into the nipple on the throttle body.

Here is the diagram for the Si. Purge solenoid and map sensor are on the fire wall. The line going to the tank is labeled "To two-way valve" because there is a 2-way valve on the fuel tank.



These older EVAP systems can still be overwhelmed. With hard working AC, and 110* summer temps, I typically get fumes coming out of the fresh air port on the canister. This is why they went to the sealed, pressure monitored systems for OBD2.

 

I'm thinking of doing this, instead of having a line vent into my engine bay. Can you tell me how long you've had it hooked up this way and is there any unusual side effects from it being this hooked up this way?