- Jun 30, 2012
- 7,306
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I could use a favor, if anyone with access to their tech resources has a spare moment.
I'm working on another [insert many expletives] GM evap issue. I'm basically just wanting to know if they publish the specific specs regarding the logic used in running their evap monitor. Google has failed me.
Essentially, I need to know what values the PCM is looking for in regard to the fuel tank pressure sensor. When the canister valve is shut and the engine is pulling vacuum through the evap system, is there a certain FTP voltage at which the purge valve is then commanded closed? And what are the requirements for decay of said value once the system is sealed?
I have no proof of a bad FTP, but am running out of places to look for a problem. No leaks, no issues with the valves, but don't want to drop gas tank without being sure. Since the voltage seems to vary so incrementally (i.e. it's not a wide sweep from ~.5-4.5v in normal operations), it's hard to clearly deem it 'good' or 'bad' without knowing the exact criteria the PCM is looking for when running the monitor.
Thanks in advance.
And for those that have never had to deal with non-leak-related evaporative emissions issues on a GM- pray to the deity of your choice that it stays that way.:\
I'm working on another [insert many expletives] GM evap issue. I'm basically just wanting to know if they publish the specific specs regarding the logic used in running their evap monitor. Google has failed me.
Essentially, I need to know what values the PCM is looking for in regard to the fuel tank pressure sensor. When the canister valve is shut and the engine is pulling vacuum through the evap system, is there a certain FTP voltage at which the purge valve is then commanded closed? And what are the requirements for decay of said value once the system is sealed?
I have no proof of a bad FTP, but am running out of places to look for a problem. No leaks, no issues with the valves, but don't want to drop gas tank without being sure. Since the voltage seems to vary so incrementally (i.e. it's not a wide sweep from ~.5-4.5v in normal operations), it's hard to clearly deem it 'good' or 'bad' without knowing the exact criteria the PCM is looking for when running the monitor.
Thanks in advance.
And for those that have never had to deal with non-leak-related evaporative emissions issues on a GM- pray to the deity of your choice that it stays that way.:\
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