TurfBurn
08-30-2004, 02:38 PM
Just some useful information for the general forum populace. These things cause a lot of CEL's for whatever reason. And some people wonder about removing this whole system. So here you go.. hope its helpful.
http://www.findarticles.com/p/articles/mi_m0BQA/is_2_80/ai_71847187
or here is the content:
Codes for evaporative emissions system leaks have been a problem since the conception of OBD II. Now out of warranty, these vehicles are showing up for repair in the aftermarket. These codes get blown off as a loose gas cap 90% of the time. Technicians often say, "Just tighten the gas cap, clear the codes and hope it doesn't come back." You might get away with that a few times but what if the car comes back for the third time with the same code? Whether the gas cap was really loose or not, the code was set for the same reason ...the evap system didn't hold vacuum when the POM tested it.
Evap leak codes do not indicate an electrical fault such as an open or a short-they are the result of a failed functional test, meaning the components did not perform properly when the PCM ran a test on the evap system. If, for any reason, the PCM did not see that the system held vacuum during the test, it will set a code for either a small or large leak.
This article focuses on the 1996-1998 Mazda Protege, but all Asian vehicles function basically the same ... they just use different components. All utilize a purge control valve to apply engine vacuum to the system, all have a solenoid valve to seal the charcoal canister from atmosphere, and all use a pressure sensor to monitor the vacuum on the system. The Protege uses a duty controlled purge solenoid, a canister drain cut valve (CDCV), a tank pressure control valve (TPCV), and a fuel tank pressure sensor (FTPS).
An evaporative emission system test is like sucking on a straw. Put your finger over the end of a straw and then suck on it until it collapses, then seal the other end with your tongue -- it will stay collapsed until you release your finger. Your finger is the canister drain cut valve, and you are the purge valve when you apply vacuum on the straw with your mouth and tongue. Instead of a pressure sensor, your senses tell you that there is vacuum on the straw Pretend there is a tiny hole in the straw so it slowly loses vacuum and won't stay collapsed-that is a small leak. If there is a big crack in the straw and it never even tried to collapse (e.g.: no vacuum)-that would be a large leak. If you under stand this, then you understand evaporative system testing.
Testing is simple if you know what the PCM does. All you have to do is simulate that process, using a voltmeter, two jumper wires and two suitable pins to backprobe the PCM terminals (paper clips work well).
To Test:
1) Remove the center console. The PCM is under the center of the dash just in front of the shifter.
2) Hook up a voltmeter to the FTPS signal wire (terminal "3-K" on the Protege). The sensor will read approximately 2.5v at 0 inch vacuum.
3) With the key on/engine off, place one of the jumper wires into the back of the PCM terminal which is the ground for the CDCV and TPCV (terminal "3-0"). The PCM controls the ground for both solenoids at the same time-they are wired together. Ground the wire just like the PCM does, tap it -- listen for the CDCV clicking in the left rear wheel well. If no clicks, check CDCV operation.
4) Place the second jumper wire into the back of the terminal for the Purge Control Solenoid (terminal "l-R "). The PCM is controlling the ground for this solenoid as well- and it will be jumped to ground just like the CDCV and TPCV
5) Start the engine and let idle. Jump terminal "3-0" to groundleave grounded.
6) Tap terminal "1-R" to ground for a few seconds while monitoring the FTPS voltage. If there are no leaks, vacuum should be applied and the FTPS voltage should drop-approximately 0.lv for every 0.1 inch of vacuum applied The PCM will only apply about 0.8 inch of vacuum. It usually only takes a second if there are no leaks. This will read about 1.7v on your meter.
7) After you see the FTPS voltage drop to about 1.7v, release the ground on the purge solenoid (terminal "l-R") but leave the CDCV and TPCV grounded. The vacuum should come up slightly, level off, and then should hold until the ground is released on the CDCV. The FTPS voltage should level off at about 2.0v and hold until the CDCV ground is released. If you don't get these results, there's a problem.
Examples of a failed test:
1) The FTPS voltage never drops. This would indicate a large leak. Possible causes: a CDCV that didn't seal the canister or a TPCV that didn't open up to allow the vacuum to be applied to the FTPS.
2) The FTPS voltage dropped but then slowly came back up to 2.5v. This means a small leak, like the pin hole in that straw Check for a cracked hose, a loose hose connection or the infamous loose gas cap.
To test the system for leaks:
1) Testing is done with the vehicle on a lift, in the air, with the engine idling.
2) Ground both jumper wires (terminals "l-R" and "3-0")-leave grounded. This should be applying full engine vacuum to the evap system through the purge solenoid.
3) Follow the vacuum hoses from the purge solenoid to the gas tank to see where you are losing the vacuum (listen for the hissing noise).
The most common failure is the CDCV. If it isn't sealing the canister, pinch the hose off going to the CDCV from the canister to see if you start pulling vacuum on the system. Also check for a cracked charcoal canister. All of these components are at the rear of the vehicle except for the purge solenoid.
COPYRIGHT 2001 Adams Business Media
COPYRIGHT 2001 Gale Group
http://www.findarticles.com/p/articles/mi_m0BQA/is_2_80/ai_71847187
or here is the content:
Codes for evaporative emissions system leaks have been a problem since the conception of OBD II. Now out of warranty, these vehicles are showing up for repair in the aftermarket. These codes get blown off as a loose gas cap 90% of the time. Technicians often say, "Just tighten the gas cap, clear the codes and hope it doesn't come back." You might get away with that a few times but what if the car comes back for the third time with the same code? Whether the gas cap was really loose or not, the code was set for the same reason ...the evap system didn't hold vacuum when the POM tested it.
Evap leak codes do not indicate an electrical fault such as an open or a short-they are the result of a failed functional test, meaning the components did not perform properly when the PCM ran a test on the evap system. If, for any reason, the PCM did not see that the system held vacuum during the test, it will set a code for either a small or large leak.
This article focuses on the 1996-1998 Mazda Protege, but all Asian vehicles function basically the same ... they just use different components. All utilize a purge control valve to apply engine vacuum to the system, all have a solenoid valve to seal the charcoal canister from atmosphere, and all use a pressure sensor to monitor the vacuum on the system. The Protege uses a duty controlled purge solenoid, a canister drain cut valve (CDCV), a tank pressure control valve (TPCV), and a fuel tank pressure sensor (FTPS).
An evaporative emission system test is like sucking on a straw. Put your finger over the end of a straw and then suck on it until it collapses, then seal the other end with your tongue -- it will stay collapsed until you release your finger. Your finger is the canister drain cut valve, and you are the purge valve when you apply vacuum on the straw with your mouth and tongue. Instead of a pressure sensor, your senses tell you that there is vacuum on the straw Pretend there is a tiny hole in the straw so it slowly loses vacuum and won't stay collapsed-that is a small leak. If there is a big crack in the straw and it never even tried to collapse (e.g.: no vacuum)-that would be a large leak. If you under stand this, then you understand evaporative system testing.
Testing is simple if you know what the PCM does. All you have to do is simulate that process, using a voltmeter, two jumper wires and two suitable pins to backprobe the PCM terminals (paper clips work well).
To Test:
1) Remove the center console. The PCM is under the center of the dash just in front of the shifter.
2) Hook up a voltmeter to the FTPS signal wire (terminal "3-K" on the Protege). The sensor will read approximately 2.5v at 0 inch vacuum.
3) With the key on/engine off, place one of the jumper wires into the back of the PCM terminal which is the ground for the CDCV and TPCV (terminal "3-0"). The PCM controls the ground for both solenoids at the same time-they are wired together. Ground the wire just like the PCM does, tap it -- listen for the CDCV clicking in the left rear wheel well. If no clicks, check CDCV operation.
4) Place the second jumper wire into the back of the terminal for the Purge Control Solenoid (terminal "l-R "). The PCM is controlling the ground for this solenoid as well- and it will be jumped to ground just like the CDCV and TPCV
5) Start the engine and let idle. Jump terminal "3-0" to groundleave grounded.
6) Tap terminal "1-R" to ground for a few seconds while monitoring the FTPS voltage. If there are no leaks, vacuum should be applied and the FTPS voltage should drop-approximately 0.lv for every 0.1 inch of vacuum applied The PCM will only apply about 0.8 inch of vacuum. It usually only takes a second if there are no leaks. This will read about 1.7v on your meter.
7) After you see the FTPS voltage drop to about 1.7v, release the ground on the purge solenoid (terminal "l-R") but leave the CDCV and TPCV grounded. The vacuum should come up slightly, level off, and then should hold until the ground is released on the CDCV. The FTPS voltage should level off at about 2.0v and hold until the CDCV ground is released. If you don't get these results, there's a problem.
Examples of a failed test:
1) The FTPS voltage never drops. This would indicate a large leak. Possible causes: a CDCV that didn't seal the canister or a TPCV that didn't open up to allow the vacuum to be applied to the FTPS.
2) The FTPS voltage dropped but then slowly came back up to 2.5v. This means a small leak, like the pin hole in that straw Check for a cracked hose, a loose hose connection or the infamous loose gas cap.
To test the system for leaks:
1) Testing is done with the vehicle on a lift, in the air, with the engine idling.
2) Ground both jumper wires (terminals "l-R" and "3-0")-leave grounded. This should be applying full engine vacuum to the evap system through the purge solenoid.
3) Follow the vacuum hoses from the purge solenoid to the gas tank to see where you are losing the vacuum (listen for the hissing noise).
The most common failure is the CDCV. If it isn't sealing the canister, pinch the hose off going to the CDCV from the canister to see if you start pulling vacuum on the system. Also check for a cracked charcoal canister. All of these components are at the rear of the vehicle except for the purge solenoid.
COPYRIGHT 2001 Adams Business Media
COPYRIGHT 2001 Gale Group