EVAP: I need to know how it works....
06-14-2007, 11:17 AM
#1
EVAP: I need to know how it works.... Hey everyone.
Ive been trying to get some little things straight on my 87 swap car. I just got my fuel level gauge working. Found out I had to disconnect the purple fuel level sender wire from the PCM. Then the autometer gauge will work properly. However, now the PCM doesnt have a fuel level reading.
Here is what I need to know.
Does that wire need to be hooked up for EVAP to function correctly? If it does...when exactly does the PCM decide to vent the tank? Is it at pre-determined values from the sender? Or is it some weird algorithm. Basically, if the PCM needs that fuel level signal for evap to work, I need to know if there is a way to trick it into working. Whether it be with a resistor to simulate fuel level, or by tuning.
Any info would be GREATLY appreciated!
Justin
Ive been trying to get some little things straight on my 87 swap car. I just got my fuel level gauge working. Found out I had to disconnect the purple fuel level sender wire from the PCM. Then the autometer gauge will work properly. However, now the PCM doesnt have a fuel level reading.
Here is what I need to know.
Does that wire need to be hooked up for EVAP to function correctly? If it does...when exactly does the PCM decide to vent the tank? Is it at pre-determined values from the sender? Or is it some weird algorithm. Basically, if the PCM needs that fuel level signal for evap to work, I need to know if there is a way to trick it into working. Whether it be with a resistor to simulate fuel level, or by tuning.
Any info would be GREATLY appreciated!
Justin
06-14-2007, 11:31 AM
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the pcm looks at Pressure,level, road speed and throttle angle plus EGR to see if its on. It then decides to vent or not. you can just delete the code though if your state does not require emissions compliance for your engine swap.
Originally Posted by ghettocruiser
Hey everyone.
Ive been trying to get some little things straight on my 87 swap car. I just got my fuel level gauge working. Found out I had to disconnect the purple fuel level sender wire from the PCM. Then the autometer gauge will work properly. However, now the PCM doesnt have a fuel level reading.
Here is what I need to know.
Does that wire need to be hooked up for EVAP to function correctly? If it does...when exactly does the PCM decide to vent the tank? Is it at pre-determined values from the sender? Or is it some weird algorithm. Basically, if the PCM needs that fuel level signal for evap to work, I need to know if there is a way to trick it into working. Whether it be with a resistor to simulate fuel level, or by tuning.
Any info would be GREATLY appreciated!
Justin
Ive been trying to get some little things straight on my 87 swap car. I just got my fuel level gauge working. Found out I had to disconnect the purple fuel level sender wire from the PCM. Then the autometer gauge will work properly. However, now the PCM doesnt have a fuel level reading.
Here is what I need to know.
Does that wire need to be hooked up for EVAP to function correctly? If it does...when exactly does the PCM decide to vent the tank? Is it at pre-determined values from the sender? Or is it some weird algorithm. Basically, if the PCM needs that fuel level signal for evap to work, I need to know if there is a way to trick it into working. Whether it be with a resistor to simulate fuel level, or by tuning.
Any info would be GREATLY appreciated!
Justin
06-14-2007, 12:33 PM
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if you put fuel under vacum it lowers its boiling and vaporization point. if it wasn't vented the fuel would boil and evaporate off.
Originally Posted by 2002_Z28_Six_Speed
What's the purpose of the gas tank vent?
06-14-2007, 02:03 PM
#5
Im not sure on that....atleast I dont think thats the whole story.
I thought EVAP was for evacuating the gasses that build when gasoline sits in a container. It vents this pressure up to be burnt in the motor, instead of venting to atmosphere (hydrocarbons..?)
When gas warms up, it starts to evaporate, and will pressurize the tank. In the old days it was just vented through a tube. Now to reduce the evaporative emissions, its pumped up though the intake to be burnt.
I dont have EGR or AIR or anything else. Just the EVAP system. What I need to know is, will it still function without the PCM knowing the fuel level... Thats basically it. I definetly cant re-connect the sender wire to the pcm. I know I can turn the codes off...but then what? Is the EVAP system not doing anything? If it isnt doing anything, there is no sense in me having it and all its associated parts on my car. Ill just vent the tank. But Ide like it to function. Especially since I wired it, plumbed it, and all that jazz.
J.
I thought EVAP was for evacuating the gasses that build when gasoline sits in a container. It vents this pressure up to be burnt in the motor, instead of venting to atmosphere (hydrocarbons..?)
When gas warms up, it starts to evaporate, and will pressurize the tank. In the old days it was just vented through a tube. Now to reduce the evaporative emissions, its pumped up though the intake to be burnt.
I dont have EGR or AIR or anything else. Just the EVAP system. What I need to know is, will it still function without the PCM knowing the fuel level... Thats basically it. I definetly cant re-connect the sender wire to the pcm. I know I can turn the codes off...but then what? Is the EVAP system not doing anything? If it isnt doing anything, there is no sense in me having it and all its associated parts on my car. Ill just vent the tank. But Ide like it to function. Especially since I wired it, plumbed it, and all that jazz.
J.
06-14-2007, 02:13 PM
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The only way you could do this would be to find a way to build a voltage following circut with a few opamps. on input in and 2 outputs out. the Gm 4th gen ls1 dash send the Fuel guage datae on class 2 serial communications.
