So I yanked my problematic stock evap canister, and replaced it with a $45 Duralast VC-120 GM canister. Works great, I get good vacuum at the green test port when the purge valve on the intake is open.
So some background on 100 series evap system OBD checks - The ECU will regularly test the integrity of the evap system by closing the vent VSV on the intake, and opening the VSV on the canister (the "LA4" test). This open VSV connects the tank vent and the evap charcoal side (going to intake) while it is open and allows some pressure to build in the system, and that is read by the evap pressure sensor on the canister. Since it normally sees intake vacuum, as long as the evap pressure sensor reads atmospheric pressure or better, it should be happy, and not throw a code. If it does not sense pressure, it assumes there is a leak and throws a code
SO... to make a long story longer... I left the VSV on the canister plugged in, but only hooked to the pressure sensor. That way, the ECU sees it is there, and the VSV operates as it should when the ECU decides to do a test. All it sees is atmospheric pressure, since the other two ports on the VSV are not hooked to vacuum/vent lines.
Here's the odd thing - The VSV gets kinda hot. Not burning, melting hot ... but uncomfortable to the touch. It's not hooked to anything but the electrical connector and and evap pressure sensor. I've swapped it for another known good one I have, and that one gets hot, too.
I realize this is sort of an obscure and somewhat esoteric tech question. But I thought maybe someone might have a good idea why it would heat up? The VSV's are basically just a solenoid that operates when the ECU grounds it and closes the circuit. The solenoid is not cycled repeatedly, it's just turned off, or turned on, and left in that state until the test is over, or key power is removed. The canister VSV is normally closed, and the intake vent VSV is normally open when key power are on.
Figure it'll be good for some conversation, anyway.
And yes, I will post a write-up on how to set this up at some point in the near future.
Thanks!
Mark
So some background on 100 series evap system OBD checks - The ECU will regularly test the integrity of the evap system by closing the vent VSV on the intake, and opening the VSV on the canister (the "LA4" test). This open VSV connects the tank vent and the evap charcoal side (going to intake) while it is open and allows some pressure to build in the system, and that is read by the evap pressure sensor on the canister. Since it normally sees intake vacuum, as long as the evap pressure sensor reads atmospheric pressure or better, it should be happy, and not throw a code. If it does not sense pressure, it assumes there is a leak and throws a code
SO... to make a long story longer... I left the VSV on the canister plugged in, but only hooked to the pressure sensor. That way, the ECU sees it is there, and the VSV operates as it should when the ECU decides to do a test. All it sees is atmospheric pressure, since the other two ports on the VSV are not hooked to vacuum/vent lines.
Here's the odd thing - The VSV gets kinda hot. Not burning, melting hot ... but uncomfortable to the touch. It's not hooked to anything but the electrical connector and and evap pressure sensor. I've swapped it for another known good one I have, and that one gets hot, too.
I realize this is sort of an obscure and somewhat esoteric tech question. But I thought maybe someone might have a good idea why it would heat up? The VSV's are basically just a solenoid that operates when the ECU grounds it and closes the circuit. The solenoid is not cycled repeatedly, it's just turned off, or turned on, and left in that state until the test is over, or key power is removed. The canister VSV is normally closed, and the intake vent VSV is normally open when key power are on.
Figure it'll be good for some conversation, anyway.
And yes, I will post a write-up on how to set this up at some point in the near future.
Thanks!
Mark
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