97 LT1 EVAP Purge Solenoid Pressure Relief Plug Blowing Out
07-21-2015, 09:45 PM
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97 LT1 EVAP Purge Solenoid Pressure Relief Plug Blowing Out
Ok I've searched and read a lot of different places, but I can't find anyone else who has had the problem I'm having with my 97 LT1.
I'm on my 3rd EVAP solenoid. Each time, the plug on the back side of it blows out, and the solenoid sticks open. The original solenoid, and now 2 consecutive new BWD solenoids. All did the same thing. I'm assuming this plug on the back is doing what it's supposed to- blowing out as a failsafe because pressure is building up where it shouldn't when the solenoid is closed. The mystery to me is, why and how is pressure making its way all the way up to the intake manifold?
The line from the vacuum sensor (between the solenoid and the canister) holds vacuum all the way back to the canister. I blew pressure through the line before vacuum testing it, to clear out any potential charcoal bits.
The canister is new.
The gas cap is new. (And holds pressure, it always has too much pressure, so I've been releasing it every time I drive the car.)
The vacuum sensor is new.
The lines from the canister to the tank are new.
I did not replace the vacuum purge solenoid which sits in the line which goes from the canister to the tank. I have ordered a new one (as well as another new evap solenoid), but want to actually understand how it all works before I start putting on more parts.
I've read conflicting information regarding how the entire system works in general. I understand that the evap solenoid on the intake is opened by the computer in order to vent fumes from the canister. I understand that the vacuum sensor tells the computer whether or not purge has happened, which is how the computer knows the evap solenoid isn't working. I understand that the canister has charcoal in it which absorbs fumes or whatever, until the evap solenoid allows vacuum to evacuate the canister.
What I do not understand is the role the purge valve between the canister and the tank plays, or what the 3rd line (which goes to open air) is for on the canister. The canister has 3 lines. One to the intake, one to the tank, and one to open air.
I also do not understand how there can be so much pressure in the tank even when the evap solenoid at the intake has popped its plug and is essentially a 2nd line going to open air.
Can someone explain to me how and when the canister is supposed to hold pressure or vacuum, and how the purge valve between the canister and the tank affects that pressure or vacuum?
Or speculate as to how pressure is building up in the line that goes to the intake?
Or explain women to me?
I'm on my 3rd EVAP solenoid. Each time, the plug on the back side of it blows out, and the solenoid sticks open. The original solenoid, and now 2 consecutive new BWD solenoids. All did the same thing. I'm assuming this plug on the back is doing what it's supposed to- blowing out as a failsafe because pressure is building up where it shouldn't when the solenoid is closed. The mystery to me is, why and how is pressure making its way all the way up to the intake manifold?
The line from the vacuum sensor (between the solenoid and the canister) holds vacuum all the way back to the canister. I blew pressure through the line before vacuum testing it, to clear out any potential charcoal bits.
The canister is new.
The gas cap is new. (And holds pressure, it always has too much pressure, so I've been releasing it every time I drive the car.)
The vacuum sensor is new.
The lines from the canister to the tank are new.
I did not replace the vacuum purge solenoid which sits in the line which goes from the canister to the tank. I have ordered a new one (as well as another new evap solenoid), but want to actually understand how it all works before I start putting on more parts.
I've read conflicting information regarding how the entire system works in general. I understand that the evap solenoid on the intake is opened by the computer in order to vent fumes from the canister. I understand that the vacuum sensor tells the computer whether or not purge has happened, which is how the computer knows the evap solenoid isn't working. I understand that the canister has charcoal in it which absorbs fumes or whatever, until the evap solenoid allows vacuum to evacuate the canister.
What I do not understand is the role the purge valve between the canister and the tank plays, or what the 3rd line (which goes to open air) is for on the canister. The canister has 3 lines. One to the intake, one to the tank, and one to open air.
I also do not understand how there can be so much pressure in the tank even when the evap solenoid at the intake has popped its plug and is essentially a 2nd line going to open air.
Can someone explain to me how and when the canister is supposed to hold pressure or vacuum, and how the purge valve between the canister and the tank affects that pressure or vacuum?
Or speculate as to how pressure is building up in the line that goes to the intake?
Or explain women to me?
Last edited by 350350; 07-21-2015 at 09:50 PM.
07-22-2015, 10:08 AM
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re: 97 LT1 EVAP Purge Solenoid Pressure Relief Plug Blowing Out
I don't have a 97 factory manual, only the 96 factory manual. The 96 manual does not show a "solenoid" in the line from the tank to the canister. It shows a mechanical, self-actuated pressure control valve. Do you have a reference that shows the purge system solenoid on a 97?
I know that there is a solenoid in the line for the LS1 engines, but that appears to be there so the PCM can close it to isolate the tank from the canister, and pull a vacuum on the tank to run tests for leaks. Maybe they introduced that in 97.... don't know.
I've never heard of a pressure relief plug on the solenoids, but maybe that's what it is.
The entire fuel tank is protected by a pressure/vacuum relief valve ("fuel tank vent valve") at the rear of the car:
http://shbox.com/1/fuel_pump_wiring.jpg
That keeps the tank pressure from exceeding 5 kPa (0.73psi). As far as the canister is concerned, it is vented to atmosphere ("air" connection) and should never build up any pressure. Are you sure you have the lines connected correctly to the canister?
The factory manual shows the line from the tank connects to the nipple on the cylinder on top of the canister (#1). There is no hose connected to the center nipple (#2). The purge tube to the front of the car connects to the third nipple (#3).
Final thought.... have you experienced any popping (backfiring) into the intake manifold? That might actually build more instantaneous pressure than could be present in a correctly connected EVAP system.
I know that there is a solenoid in the line for the LS1 engines, but that appears to be there so the PCM can close it to isolate the tank from the canister, and pull a vacuum on the tank to run tests for leaks. Maybe they introduced that in 97.... don't know.
I've never heard of a pressure relief plug on the solenoids, but maybe that's what it is.
The entire fuel tank is protected by a pressure/vacuum relief valve ("fuel tank vent valve") at the rear of the car:
http://shbox.com/1/fuel_pump_wiring.jpg
That keeps the tank pressure from exceeding 5 kPa (0.73psi). As far as the canister is concerned, it is vented to atmosphere ("air" connection) and should never build up any pressure. Are you sure you have the lines connected correctly to the canister?
The factory manual shows the line from the tank connects to the nipple on the cylinder on top of the canister (#1). There is no hose connected to the center nipple (#2). The purge tube to the front of the car connects to the third nipple (#3).
Final thought.... have you experienced any popping (backfiring) into the intake manifold? That might actually build more instantaneous pressure than could be present in a correctly connected EVAP system.
07-22-2015, 11:43 AM
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re: 97 LT1 EVAP Purge Solenoid Pressure Relief Plug Blowing Out
I haven't had any backfiring through the intake at all. Running smooth for quite some time now. *knocks on wood*
I think you may be onto something with the possibility that I put the hoses back on the new canister incorrectly. That would seem to make more sense than anything else. I'll check that and get back to you.
I'm probably using some partially incorrect terminology too, and that isn't helping. I have the factory 97 service manuals, but for the life of me, as far as I can tell, they do not include the fuel system, tank, or hose routings for the evap canister. My 95 manuals had all of that but I sold them, and like you said, I'm not certain the 97 is the same.
The valve I'm referring to between the canister and the tank is called a 'purge valve' depending on who you ask. My parts catalog (Advance Auto Parts) lists it as a purge valve anyway. It is strictly mechanical, it is not a solenoid.
I will also check the tank vent valve that you mentioned while I'm under there. I remember that from when I put the new fuel pump in a couple of years ago.
Thanks, I'll keep you posted!
I think you may be onto something with the possibility that I put the hoses back on the new canister incorrectly. That would seem to make more sense than anything else. I'll check that and get back to you.
I'm probably using some partially incorrect terminology too, and that isn't helping. I have the factory 97 service manuals, but for the life of me, as far as I can tell, they do not include the fuel system, tank, or hose routings for the evap canister. My 95 manuals had all of that but I sold them, and like you said, I'm not certain the 97 is the same.
The valve I'm referring to between the canister and the tank is called a 'purge valve' depending on who you ask. My parts catalog (Advance Auto Parts) lists it as a purge valve anyway. It is strictly mechanical, it is not a solenoid.
I will also check the tank vent valve that you mentioned while I'm under there. I remember that from when I put the new fuel pump in a couple of years ago.
Thanks, I'll keep you posted!
08-07-2015, 09:44 AM
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re: 97 LT1 EVAP Purge Solenoid Pressure Relief Plug Blowing Out
I've tested every component now *except* the fuel tank vent valve. I can't find anywhere that tells me what PSI it should hold.
Between the tank and canister, there's a purge valve that basically just holds a few PSI before it allows flow in either direction.
All of the lines are routed properly.
So essentially, operating on only a loose understanding of the entire system, I can see that all of the components are working properly with the exception of now knowing how much pressure to test the vent valve at. With everything connected properly, there are two ways for pressure or vacuum to escape the tank: Through the purge solenoid to the intake manifold (which is the path that keeps blowing the plug out of my solenoid) or through the fuel tank vent valve. I have to assume that the vent valve (just ahead of the left rear wheel tethered to the rest of the fuel lines) should hold release pressure long before the plug blows out of the solenoid.
For now I just have to put it back together. If I could even know a wild speculative pressure to test the tank vent valve at, that'd help, but I can't find that anywhere. My best guess is between 5psi (the most that purge valve could possibly hold) and 40psi (pressure the pump holds). But I don't like troubleshooting on guesswork.
Honestly I think the system would work fine and not set a code if I just put a vented cap on the tank. The computer senses flow in the vacuum line near the manifold in order to decide whether or not the system is 'working properly'.
Hrmph.
Between the tank and canister, there's a purge valve that basically just holds a few PSI before it allows flow in either direction.
All of the lines are routed properly.
So essentially, operating on only a loose understanding of the entire system, I can see that all of the components are working properly with the exception of now knowing how much pressure to test the vent valve at. With everything connected properly, there are two ways for pressure or vacuum to escape the tank: Through the purge solenoid to the intake manifold (which is the path that keeps blowing the plug out of my solenoid) or through the fuel tank vent valve. I have to assume that the vent valve (just ahead of the left rear wheel tethered to the rest of the fuel lines) should hold release pressure long before the plug blows out of the solenoid.
For now I just have to put it back together. If I could even know a wild speculative pressure to test the tank vent valve at, that'd help, but I can't find that anywhere. My best guess is between 5psi (the most that purge valve could possibly hold) and 40psi (pressure the pump holds). But I don't like troubleshooting on guesswork.
Honestly I think the system would work fine and not set a code if I just put a vented cap on the tank. The computer senses flow in the vacuum line near the manifold in order to decide whether or not the system is 'working properly'.
Hrmph.
08-07-2015, 11:44 AM
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re: 97 LT1 EVAP Purge Solenoid Pressure Relief Plug Blowing Out
There is no pressure in the line. It is connected to a vacuum source at the throttle body. Valve should hold closed at the max vacuum the engine can pull, which would be about 5"Hg with closed throttle on a hard decel.
The pressure from the tank forces fuel vapor through the charcoal in the canister. The charcoal adsorbs the hydrocarbons, and any air vents out the vent on the canister. There should never be pressure in the canister.
The maximum pressure that the tank can hold, before the pressure/vent vacuum valve opens is 1 psi pressure and 1 to 2" Hg vacuum. Hence, no component in the fuel vent system should should ever see more than 1 psi.
When the purge valve open, vacuum from the intake manifold pulls air from the external vent on the canister, through the charcoal bed where it desorbs the hydrocarbons, and dumps the air HC mix into the intake manifold, where it is burned along with the normal air and fuel mix.
Could you post a photo of what you perceive to be a pressure relief plug in the solenoid?
The pressure from the tank forces fuel vapor through the charcoal in the canister. The charcoal adsorbs the hydrocarbons, and any air vents out the vent on the canister. There should never be pressure in the canister.
The maximum pressure that the tank can hold, before the pressure/vent vacuum valve opens is 1 psi pressure and 1 to 2" Hg vacuum. Hence, no component in the fuel vent system should should ever see more than 1 psi.
When the purge valve open, vacuum from the intake manifold pulls air from the external vent on the canister, through the charcoal bed where it desorbs the hydrocarbons, and dumps the air HC mix into the intake manifold, where it is burned along with the normal air and fuel mix.
Could you post a photo of what you perceive to be a pressure relief plug in the solenoid?
08-07-2015, 12:15 PM
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re: 97 LT1 EVAP Purge Solenoid Pressure Relief Plug Blowing Out
Here's a picture of the solenoid... the boss on the far left of this picture is where the plug pops out. It is press fit into the boss. No adhesive, just a press fit. It takes only fingernail pressure to pull it out.
From the parting lines on the solenoid, I don't think the plug is a manufacturing feature. When the plug is out of the hole, you can see daylight straight through the solenoid. 3 solenoids in a row (the original GM solenoid, and two new BWD solenoids) all 3 popped this plug out. It takes approximately one tank of gas for this to happen.
http://shop.advanceautoparts.com/wcs...3_pri_larg.jpg
Below is the fuel tank vent valve in front of the left rear wheel. I took this off and blew pressure through it. It will allow flow in both directions, but it takes significantly more than 1psi for it to release pressure. Vacuum goes straight through (toward the tank).
http://i67.photobucket.com/albums/h2...tInstalled.jpg
The tank module has 4 lines. 2 fuel, one to the canister, and the 4th line goes to the vent valve. Is this just an emergency-type safety in case the tank does for some reason pressurize to a dangerous level?
I agree completely that the system should never see pressure into the line that goes to the solenoid/intake, but I can't come up with any other explanation for that plug popping out frequently.
From the parting lines on the solenoid, I don't think the plug is a manufacturing feature. When the plug is out of the hole, you can see daylight straight through the solenoid. 3 solenoids in a row (the original GM solenoid, and two new BWD solenoids) all 3 popped this plug out. It takes approximately one tank of gas for this to happen.
http://shop.advanceautoparts.com/wcs...3_pri_larg.jpg
Below is the fuel tank vent valve in front of the left rear wheel. I took this off and blew pressure through it. It will allow flow in both directions, but it takes significantly more than 1psi for it to release pressure. Vacuum goes straight through (toward the tank).
http://i67.photobucket.com/albums/h2...tInstalled.jpg
The tank module has 4 lines. 2 fuel, one to the canister, and the 4th line goes to the vent valve. Is this just an emergency-type safety in case the tank does for some reason pressurize to a dangerous level?
I agree completely that the system should never see pressure into the line that goes to the solenoid/intake, but I can't come up with any other explanation for that plug popping out frequently.
08-07-2015, 01:11 PM
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re: 97 LT1 EVAP Purge Solenoid Pressure Relief Plug Blowing Out
How much pressure does it take to pop the plug out of the solenoid?
Do you have the lines connected to the solenoid correctly:
Courtesy of Shoebox
http://shbox.com/1/evap_sol.jpg
You mention "and not set a code"..... are you getting a code? Or is that just speculation in the event you use a vented fill cap?
The 1 psi max is right from the test procedure for the pressure/vent valve, 1996 factory manual, page 6C-7:
"Slowly apply pressure to vent valve. The valve should open at approximately 1 psi. If not, replace the vent valve."
The vent valve is there to prevent the tank from being damaged due to over-pressure or high vacuum. It should not control the pressure in the tank. That is controlled by a pressure control valve in the line from the tank to the canister.
Do you have the lines connected to the solenoid correctly:
Courtesy of Shoebox
http://shbox.com/1/evap_sol.jpg
You mention "and not set a code"..... are you getting a code? Or is that just speculation in the event you use a vented fill cap?
The 1 psi max is right from the test procedure for the pressure/vent valve, 1996 factory manual, page 6C-7:
"Slowly apply pressure to vent valve. The valve should open at approximately 1 psi. If not, replace the vent valve."
The vent valve is there to prevent the tank from being damaged due to over-pressure or high vacuum. It should not control the pressure in the tank. That is controlled by a pressure control valve in the line from the tank to the canister.
08-07-2015, 02:10 PM
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re: 97 LT1 EVAP Purge Solenoid Pressure Relief Plug Blowing Out
According to shoebox's pic, I do have the vacuum hoses correct on the solenoid. I am also confident the hoses are correct on the canister, they are clearly marked on the canister itself, and I traced each hose to be certain I was connecting the right ones in the right places.
I don't know how much pressure it takes to pop the plug out. I put it all back together this morning because I need to drive it for a few days. If (when) it pops again, I'll take the solenoid back off and test how much pressure it takes to pop it out.
I wanted to be sure we're talking about the same valve for the 1psi test that you quoted. The tank vent valve is the white one in the pic above. The one I'm calling the 'purge valve' is a black valve with 3 ports (2 on the canister side and 1 on the tank side) that is in the hose which runs from the tank to the canister. The purge valve opens easily at 1psi. Here's a pic...
Canister Purge Valve - Duralast (PV134)
If the tank vent valve and the purge valve both open at 1psi, what would make the vapor head to the canister and not just out the vent? If in fact the tank vent valve does also open at 1psi, then mine is definitely bad. I didn't put a gage on it but I could not blow on it hard enough to get air to pass through it with my lungs. I had to use compressed air to get it to open. In theory, shouldn't the tank vent valve require more pressure to open than the purge valve, so that under normal operation the vapor goes to the canister?
When the plug pops out, I get a 'no flow' or 'improper flow' code. Essentially it's a huge vacuum leak at that point, so when the solenoid opens, it's just sucking air in through that hole in the back of the solenoid. I was thinking that with a vented cap, vacuum would pull through the solenoid as it was supposed to and the vacuum sensor would relay to the computer that flow is happening as required. That's speculation on my part. I'd prefer it to work properly but I'm at a loss for what's not working right.
Thanks for reading through this and helping out by the way. I appreciate your help.
I don't know how much pressure it takes to pop the plug out. I put it all back together this morning because I need to drive it for a few days. If (when) it pops again, I'll take the solenoid back off and test how much pressure it takes to pop it out.
I wanted to be sure we're talking about the same valve for the 1psi test that you quoted. The tank vent valve is the white one in the pic above. The one I'm calling the 'purge valve' is a black valve with 3 ports (2 on the canister side and 1 on the tank side) that is in the hose which runs from the tank to the canister. The purge valve opens easily at 1psi. Here's a pic...
Canister Purge Valve - Duralast (PV134)
If the tank vent valve and the purge valve both open at 1psi, what would make the vapor head to the canister and not just out the vent? If in fact the tank vent valve does also open at 1psi, then mine is definitely bad. I didn't put a gage on it but I could not blow on it hard enough to get air to pass through it with my lungs. I had to use compressed air to get it to open. In theory, shouldn't the tank vent valve require more pressure to open than the purge valve, so that under normal operation the vapor goes to the canister?
When the plug pops out, I get a 'no flow' or 'improper flow' code. Essentially it's a huge vacuum leak at that point, so when the solenoid opens, it's just sucking air in through that hole in the back of the solenoid. I was thinking that with a vented cap, vacuum would pull through the solenoid as it was supposed to and the vacuum sensor would relay to the computer that flow is happening as required. That's speculation on my part. I'd prefer it to work properly but I'm at a loss for what's not working right.
Thanks for reading through this and helping out by the way. I appreciate your help.
Last edited by 350350; 08-07-2015 at 02:12 PM.
08-07-2015, 09:19 PM
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re: 97 LT1 EVAP Purge Solenoid Pressure Relief Plug Blowing Out
This gives a good schematic as well as description of the overall operation of the system.
| Repair Guides | Emission Controls | Evaporative Emission Controls | AutoZone.com
After re-reading your last reply, I'm certain my tank vent valve is bad. I'm trying to find another one. Will report back what I find when I get one. I'll test it and compare it to the one I take off.
| Repair Guides | Emission Controls | Evaporative Emission Controls | AutoZone.com
After re-reading your last reply, I'm certain my tank vent valve is bad. I'm trying to find another one. Will report back what I find when I get one. I'll test it and compare it to the one I take off.
08-07-2015, 10:17 PM
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re: 97 LT1 EVAP Purge Solenoid Pressure Relief Plug Blowing Out
GaryDoug tested his pressure/vacuum vent valve, and it opened for pressure and vacuum as stated in the shop manual. You should use a pressure gauge and the pressure side of something like a my-t-vac to apply the test pressure.
I'm going to try applying pressure and vacuum to the charcoal canister to see how it responds.
I'm going to try applying pressure and vacuum to the charcoal canister to see how it responds.
Last edited by Injuneer; 08-07-2015 at 10:20 PM.
08-09-2015, 11:40 AM
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re: 97 LT1 EVAP Purge Solenoid Pressure Relief Plug Blowing Out
I took my 94 canister, which is no longer installed in the (track) car, and applied low pressure air flow to the tank connection (#1 in the diagram above), while plugging off the purge line connection (#3 in the diagram above). The very low pressure caused air to flow out of the air vent tube (#2 in the diagram), preventing the buildup of pressure in the system. I could still smell the gasoline fumes coming out of the air vent, even though its probably 10 years or so since the canister was removed from the car, with about 80,000 miles on it.
I remember several years ago someone coming on here, and challenging my description of how the canister operated, and how the vent valve protected the tank from pressure and vacuum. He actually got quite nasty and offensive. I think that was what caused GaryDoug to check the operation of the tank vent valve, and he verified the description in the factory manual.
The mystery just deepens. Given the fact there is a vent on the canister, I can't see how it is possible to pressure the line to the purge solenoid at the engine. I looked for my purge solenoid, hoping I could measure how much pressure it takes to pop the "plug" but I couldn't find it.
08-09-2015, 08:03 PM
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re: 97 LT1 EVAP Purge Solenoid Pressure Relief Plug Blowing Out
Ok so... I have nothing helpful to add! I can only add more mystery...
I pressure tested my tank vent valve... just as you said, it opens at approximately 1psi. It allows very little air to flow through it though, so if you put a lot of pressure on it, it can build up to about 5psi because it can't bleed out a high volume of air. Which makes sense... it's a low pressure relief valve so it shouldn't ever see any real volume of air.
I also located the last BWD solenoid that popped its plug. I reinstalled the plug, and pressure tested it. I can put over 10psi to the solenoid without popping the plug out. I tried it at least a dozen times, and each time without fail the vacuum line will blow off of the solenoid's vacuum port before the plug blows out of the back of the solenoid. I am completely baffled. Essentially, it's impossible to blow the plug out of the solenoid (keep in mind this is a defective solenoid which has had the plug removed and re-inserted) by pressurizing the vacuum line. The vacuum line can't hold onto the nipple tight enough.
I will test my canister exactly the way you did yours, above, and report back what I find. It is a new canister, but it's not out of the realm of possibility that it could be defective.
I still can't figure out why the tank itself holds so much pressure. Sometimes when I take the cap off, it whooshes for several seconds. That must be more than 1psi inside the tank, right? The only part of the system I have not visually inspected is the tank module itself, where the lines go inside the tank. It seems unlikely that anything could be blocking the vent from the inside of the tank. ?!?
There has to be a reason that 3 solenoids in a row lost that plug. That's way too many to be coincidence. What else could cause it to fall out?
If I test the canister and get the same results that you did on yours, and blow air through both the tank-to-canister hose and the tank vent valve hose, and they are unrestricted, what else can I possibly test/inspect? If I don't find anything wrong with those tests, I'll just put it back together and hope for the best.
I think I read that thread where the guy was arguing with you about the vent valve and purge valve. He was trying to say it held something like 60psi as I recall. Sure, a tire holds 50psi max and the fuel injection system runs at about 45psi, but the tank should normally hold 60psi? That's crazy. That's where I stopped reading that thread!
I pressure tested my tank vent valve... just as you said, it opens at approximately 1psi. It allows very little air to flow through it though, so if you put a lot of pressure on it, it can build up to about 5psi because it can't bleed out a high volume of air. Which makes sense... it's a low pressure relief valve so it shouldn't ever see any real volume of air.
I also located the last BWD solenoid that popped its plug. I reinstalled the plug, and pressure tested it. I can put over 10psi to the solenoid without popping the plug out. I tried it at least a dozen times, and each time without fail the vacuum line will blow off of the solenoid's vacuum port before the plug blows out of the back of the solenoid. I am completely baffled. Essentially, it's impossible to blow the plug out of the solenoid (keep in mind this is a defective solenoid which has had the plug removed and re-inserted) by pressurizing the vacuum line. The vacuum line can't hold onto the nipple tight enough.
I will test my canister exactly the way you did yours, above, and report back what I find. It is a new canister, but it's not out of the realm of possibility that it could be defective.
I still can't figure out why the tank itself holds so much pressure. Sometimes when I take the cap off, it whooshes for several seconds. That must be more than 1psi inside the tank, right? The only part of the system I have not visually inspected is the tank module itself, where the lines go inside the tank. It seems unlikely that anything could be blocking the vent from the inside of the tank. ?!?
There has to be a reason that 3 solenoids in a row lost that plug. That's way too many to be coincidence. What else could cause it to fall out?
If I test the canister and get the same results that you did on yours, and blow air through both the tank-to-canister hose and the tank vent valve hose, and they are unrestricted, what else can I possibly test/inspect? If I don't find anything wrong with those tests, I'll just put it back together and hope for the best.
I think I read that thread where the guy was arguing with you about the vent valve and purge valve. He was trying to say it held something like 60psi as I recall. Sure, a tire holds 50psi max and the fuel injection system runs at about 45psi, but the tank should normally hold 60psi? That's crazy. That's where I stopped reading that thread!
08-10-2015, 07:12 AM
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re: 97 LT1 EVAP Purge Solenoid Pressure Relief Plug Blowing Out
When you pressure tested the EVAP purge solenoid, did you apply the pressure to the line for the tank connection, or the line for the throttle body connection?
Another question might be why is the tank generating such a heavy vapor load? Vapor is generated by heat, and heat could only come from - 1) overheating fuel pump; 2) - fuel lines running too close to exhaust components; 3 - heat shields missing between exhaust components and the tank.
Still doesn't explain why the vent valve does not relieve the pressure.
Another question might be why is the tank generating such a heavy vapor load? Vapor is generated by heat, and heat could only come from - 1) overheating fuel pump; 2) - fuel lines running too close to exhaust components; 3 - heat shields missing between exhaust components and the tank.
Still doesn't explain why the vent valve does not relieve the pressure.
08-11-2015, 12:03 PM
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Re: 97 LT1 EVAP Purge Solenoid Pressure Relief Plug Blowing Out
The solenoid I tested was defective in 2 ways- it was stuck in the open position, and the plug had also been popped out of it and pushed back in. I tried applying pressure to both ports, with the same results. When the plug is removed, you can literally see directly through the entire solenoid, out the lower vacuum port, so I know that there is a clear path for the pressure to apply to the plug.
I took it apart this morning and tested everything near the canister:
The fuel tank vent valve opens for pressure or vacuum at about 1psi. (This valve is designed with snap-type tabs which allow it to be disassembled, cleaned, and inspected. It's essentially a diaphram and a spring. I cleaned it and retested it.)
The purge valve can also be (carefully) disassembled and cleaned/inspected. I took my old one apart. Also a simple diaphram and spring. This is new in my setup so I tested it one last time. 1psi to open with vacuum or pressure.
Applying pressure to the tank vent line allows air to flow freely out the fill neck with the cap removed. Applying pressure to the purge valve line also allows air to flow freely out the fill neck with the cap removed. No restrictions.
I tested the canister with the same results you got from yours- pressure applied to either the tank or purge ports results in air coming out the vent (center) port.
I have absolutely no idea why the plug keeps popping out of the solenoid.
My car is mostly stock with all of the heat shields in their original locations. Stock exhaust manifolds, and in fact it has an SLP Loudmouth cat-back on it, so there is no muffler directly beneath the tank as a stock car would have. However, I do have a Racetronix 255gph fuel pump in it. I chose this pump even though I do not need its performance, because it was essentially the same price as a stock pump and I just can't stand to put stuff back together stock. So this could heat the fuel some. The car also has a 160 degree thermostat for its programming, and runs at a nice cool 180 most of the time. On a hot day in stop and go traffic it might creep up to 200. But in general, under hood temps are near or below what a stock car would run.
One thing that I have learned through all of this is that both the vent valve and the purge valve flow a very small volume of air. It would take time to bleed off any significant amount of pressure. My initial (incorrect) assumption that pressure was popping the plug out led me to releasing the tank pressure after every drive, by removing the gas cap. That's when I'd experience the huge whoosh of air. I wonder if I wasn't giving it enough time to bleed out properly through the valves which are designed to bleed off pressure slowly, leading me to believe that it was actually 'holding' a lot of pressure. I'll experiment with checking the pressure under the gas cap both immediately following a drive, and then with letting the car sit for a couple of hours after a similar drive. This big 'whoosh' was mentioned in other places I read about people having trouble finding the root of EVAP system problems, and I wonder if they were also misleading themselves.
For now though I'm just going to drive the damned thing!!! I'll report back how it goes...
At least I understand now how the entire system is supposed to work.
I took it apart this morning and tested everything near the canister:
The fuel tank vent valve opens for pressure or vacuum at about 1psi. (This valve is designed with snap-type tabs which allow it to be disassembled, cleaned, and inspected. It's essentially a diaphram and a spring. I cleaned it and retested it.)
The purge valve can also be (carefully) disassembled and cleaned/inspected. I took my old one apart. Also a simple diaphram and spring. This is new in my setup so I tested it one last time. 1psi to open with vacuum or pressure.
Applying pressure to the tank vent line allows air to flow freely out the fill neck with the cap removed. Applying pressure to the purge valve line also allows air to flow freely out the fill neck with the cap removed. No restrictions.
I tested the canister with the same results you got from yours- pressure applied to either the tank or purge ports results in air coming out the vent (center) port.
I have absolutely no idea why the plug keeps popping out of the solenoid.
My car is mostly stock with all of the heat shields in their original locations. Stock exhaust manifolds, and in fact it has an SLP Loudmouth cat-back on it, so there is no muffler directly beneath the tank as a stock car would have. However, I do have a Racetronix 255gph fuel pump in it. I chose this pump even though I do not need its performance, because it was essentially the same price as a stock pump and I just can't stand to put stuff back together stock. So this could heat the fuel some. The car also has a 160 degree thermostat for its programming, and runs at a nice cool 180 most of the time. On a hot day in stop and go traffic it might creep up to 200. But in general, under hood temps are near or below what a stock car would run.
One thing that I have learned through all of this is that both the vent valve and the purge valve flow a very small volume of air. It would take time to bleed off any significant amount of pressure. My initial (incorrect) assumption that pressure was popping the plug out led me to releasing the tank pressure after every drive, by removing the gas cap. That's when I'd experience the huge whoosh of air. I wonder if I wasn't giving it enough time to bleed out properly through the valves which are designed to bleed off pressure slowly, leading me to believe that it was actually 'holding' a lot of pressure. I'll experiment with checking the pressure under the gas cap both immediately following a drive, and then with letting the car sit for a couple of hours after a similar drive. This big 'whoosh' was mentioned in other places I read about people having trouble finding the root of EVAP system problems, and I wonder if they were also misleading themselves.
For now though I'm just going to drive the damned thing!!! I'll report back how it goes...
At least I understand now how the entire system is supposed to work.
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