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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
let me start off by saying I do see the other thread about this issue and have read it and all other threads relating to this issue. I did not think it was right to cloud his post with my separate questions so i made my own...
I am having an issue with signficant pressure released at the gas cap, as well as a fuel smell when parking in my garage. If related, i also have a very hard time getting this car to take fuel from the pump. Ie it stops every 2 dollars or so.
The only other point id like to make in case its relevant is that I last night, released the pressure before going to bed and when I tried again this morning, there was less, but additional pressure from the cap. The engine never ran between the two times I opened the cap.
I have already changed the UFO fuel tank vent valve over the rear axle as that part is now easily available.
I have also moved the vacuum line on my charcoal cannister to a vacuum line that always has vacuum vs the original setup where it has vacuum only at speeds. I read in another thread this would help, it didnt. Thats why you see a capped line in the cannister photo.
I now believe the issue to lie within the EVAP purge system and the cannister. i think that the issue must be with either the valve on the top of the cannister, or the one in the line from the tank to the cannister. I have attached a photo of both as well as video showing the pressure relase
Can anyone help me to diagnose the EVAP system properly so I can figure out what is causing the pressurization?
Am i right to be scared to drive this car right now?
Thank you Canister Extra check valve? Is this part Dorman 994-093?
how can I verify operation of these parts so I know which to replace, and am I on the right track here?
thanks
Last edited by 87irocz28350; 06-19-2024 at 03:10 PM.
Reason: lost half the post
Indeed sounds like your evap system is not working. The problem you are experiencing is pretty typical for these cars. I also get extreme pressure in my tank but I eliminated the EVAP system. As such the pressure has to go somewhere.
Your purge solenoid is computer controlled, not vacuum, hence the two wire connector. Either the solenoid is bad or its not getting the clue from the computer to open at cruise. Changing the vacuum source wont do anything to help, and could possibly cause problems if it decides to start working again. Grab a factory service manual, it should have a very detailed troubleshooting guide on the evaporative emissions system as it is federally mandated that it works and works properly.
Your purge solenoid is computer controlled, not vacuum, hence the two wire connector. Either the solenoid is bad or its not getting the clue from the computer to open at cruise. Changing the vacuum source wont do anything to help, and could possibly cause problems if it decides to start working again. Grab a factory service manual, it should have a very detailed troubleshooting guide on the evaporative emissions system as it is federally mandated that it works and works properly.
Correct you are about the operation of it. Thanks for the pointer. It looks like by grounding the diagnostic connector you can get it to open to test its operation when not moving.
In case anyone needs this in the future, and so you can see my test. I will first verify all vacuum hose routing, then run the test on the right and report back.
Thanks.
It does not say how exactly I can test the "tank pressure control valve" which is that saucer looking thing in my second photo. It did show me how its intended to operate. Am I right that I apply vacuum and it opens the flow from tank to canister, and when i remove vacuum it closes it ? is that the best way to test. thanks
Last edited by 87irocz28350; 06-19-2024 at 09:58 PM.
I would think that the round thing is just a vacuum operated diaphragm. It might be dual action, open with vacuum and allow vapors to pass through it. Could be there to prevent vapors from escaping should the purge solenoid stick open and the engine is off. You can get a small 12v vacuum pump off Amazon for cheap, it's a life saver for trying to figure out vacuum operated devices with the engine off.
let me start off by saying I do see the other thread about this issue and have read it and all other threads relating to this issue. I did not think it was right to cloud his post with my separate questions so i made my own...
thanks
You are chasing your tail. The UFO valve at the tank is an over-pressure/under-pressure device. Air in as the fuel is consumed. Fumes out if the CCP system is compromised. Now this is from memory, too lazy (too hot actually) to look at the FSM, but over-pressure on that valve is like 1 psi. Which is above the CCP vent control valve cracking pressure.
CCP system: the disc valve holds pressure in the tank. And opens once the tank pressure exceeds, oh, about 0.75 psi? Again, too hot to check the FSM.
So pressure in the tank is normal.
In the canister side of the CCP system, it is completely open to the atmosphere. Yep, no pressure can/should build in the canister. See that little fitting with the strange cap over it, that is wide open to the inside on the canister, Allows air in during purge, and air out during tank venting. Even has 'AIR' molded into the top of the canister.
Correct you are about the operation of it. Thanks for the pointer. It looks like by grounding the diagnostic connector you can get it to open to test its operation when not moving.
In case anyone needs this in the future, and so you can see my test. I will first verify all vacuum hose routing, then run the test on the right and report back.
Thanks.
It does not say how exactly I can test the "tank pressure control valve" which is that saucer looking thing in my second photo. It did show me how its intended to operate. Am I right that I apply vacuum and it opens the flow from tank to canister, and when i remove vacuum it closes it ? is that the best way to test. thanks
where is the manual from? I have the book but would like digital access
You are chasing your tail. The UFO valve at the tank is an over-pressure/under-pressure device. Air in as the fuel is consumed. Fumes out if the CCP system is compromised. Now this is from memory, too lazy (too hot actually) to look at the FSM, but over-pressure on that valve is like 1 psi. Which is above the CCP vent control valve cracking pressure.
CCP system: the disc valve holds pressure in the tank. And opens once the tank pressure exceeds, oh, about 0.75 psi? Again, too hot to check the FSM.
So pressure in the tank is normal.
In the canister side of the CCP system, it is completely open to the atmosphere. Yep, no pressure can/should build in the canister. See that little fitting with the strange cap over it, that is wide open to the inside on the canister, Allows air in during purge, and air out during tank venting. Even has 'AIR' molded into the top of the canister.
RBob.
I think you misunderstood the post. Some pressure is normal, yes. Please watch the video I posted if you need confirmation that this is beyond that amount.
Thanks to your replies in other posts I did already know that the canister itself does not hold pressure. However, there is a vent line that runs from the fuel tank, to the canister. There is then an ECM controlled vacuum solenoid on the top of the canister that allows it to purge. If that never happened, would the result not be abnormal pressure built in the tank until the UFO valve releases it (which would smell)
I have owned other thirdgens. None have had this significant pressure, a long with a significant gas smell upon parking. I doubt they stank up garages from the factory.Based on my observation it would seem that the tank is holding pressure and venting out the UFO valve, which is what I smell when parking.
There's a lot of posts of people who have abnormal levels of pressure including fuel spraying out of their gas caps and hearing their tanks snap back to shape.. all the way up to cracked tanks after ignoring it long enough. To say I'm chasing my tail and that it's normal is inaccurate in my opinion. I'm just trying not to die.
I also have issues where the tank does not want to be filled. Are they related? No idea. However to say there's nothing wrong is not true. This isn't how this car came out of the plant.
You seem very knowledgeable. How do I test the disc valve you speak of. Stands to reason if that was not opening at the .75psi or whatever it is, pressure could build.
Thanks
Last edited by 87irocz28350; 06-24-2024 at 01:07 AM.
I was able to run the above test sequence on my car.
It looks like the canister purge solenoid is working as designed when commanded by grounding the diagnostic connector.
My next theory, is that my water temperature my never be getting to the 176 degrees required for the ECM to start purging. I have an ALDL cable and WinALDL so I am going to read the ECT and see if that tells me anything useful. If all conditions for evap purge are met besides the vehicle speed and throttle position, I will drive it and report back.
Im thinking there is a chance on all the short drives Ive done the tank has had barely any time to purge, or may never purge. PO wired the fan to a non ecm controlled temp switch, and it runs almost immediately after the engine starts up.
How do I know that the vent line running from the tank, to the canister is not clogged. Can I blow it out from the canister side? Can I get to it to blow it out from the tank side without dropping the tank?
Thank you all
Last edited by 87irocz28350; 06-24-2024 at 01:03 AM.
I was able to run the above test sequence on my car.
It looks like the canister purge solenoid is working as designed when commanded by grounding the diagnostic connector.
My next theory, is that my water temperature my never be getting to the 176 degrees required for the ECM to start purging. I have an ALDL cable and WinALDL so I am going to read the ECT and see if that tells me anything useful. If all conditions for evap purge are met besides the vehicle speed and throttle position, I will drive it and report back.
Im thinking there is a chance on all the short drives Ive done the tank has had barely any time to purge, or may never purge. PO wired the fan to a non ecm controlled temp switch, and it runs almost immediately after the engine starts up.
How do I know that the vent line running from the tank, to the canister is not clogged. Can I blow it out from the canister side? Can I get to it to blow it out from the tank side without dropping the tank?
Thank you all
What if your canister is plugged/saturated? If the tank was overfilled to many times, as in fuel coming out the full tube, then raw unburned gas could have made its way to the can.
Im thinking there is a chance on all the short drives Ive done the tank has had barely any time to purge, or may never purge. PO wired the fan to a non ecm controlled temp switch, and it runs almost immediately after the engine starts up.
The tank never gets purged via the purge solenoid and engine vacuum. That is only directed to the canister. If the canister doesn't get purged, sooner or later you will be getting fuel fumes while driving. As the charcoal becomes saturated and raw fumes exit the canister (BTDT).
The tank purges itself into the canister via the vapor control valve (the small one near the canister). It is based on pressure in the tank to overcome the valve and allow fumes into the canister.
How do I know that the vent line running from the tank, to the canister is not clogged. Can I blow it out from the canister side? Can I get to it to blow it out from the tank side without dropping the tank?
You can blow it out from the engine end. Be aware that there is a restriction in the line at the tank. So a healthy volume of compressed air will pressurize the line. Remove the gas cap and you can usually hear it hissing as air is fed in. Can also feed in some air, stop the air but hold the nozzle in place for 15 - 20 seconds. Then when removed the line should have de-pressuized by then.
Can also spray some solvent into the tube and run it through via compressed air. This should get rid of any varnish buildup on the restriction.
The tank never gets purged via the purge solenoid and engine vacuum. That is only directed to the canister. If the canister doesn't get purged, sooner or later you will be getting fuel fumes while driving. As the charcoal becomes saturated and raw fumes exit the canister (BTDT).
The tank purges itself into the canister via the vapor control valve (the small one near the canister). It is based on pressure in the tank to overcome the valve and allow fumes into the canister.
You can blow it out from the engine end. Be aware that there is a restriction in the line at the tank. So a healthy volume of compressed air will pressurize the line. Remove the gas cap and you can usually hear it hissing as air is fed in. Can also feed in some air, stop the air but hold the nozzle in place for 15 - 20 seconds. Then when removed the line should have de-pressuized by then.
Can also spray some solvent into the tube and run it through via compressed air. This should get rid of any varnish buildup on the restriction.
RBob.
thanks for all this
what do you recommend I look into here then as the smell definitely isn’t coming from the canister. When I park and smell fuel I have put my face into the canister area and there’s 0 smell coming from it. It smells like it comes from behind you when you pull into the garage. Hence my assumption that I’m smelling the pressure venting out the UFO
The tank purges itself into the canister via the vapor control valve (the small one near the canister). It is based on pressure in the tank to overcome the valve and allow fumes into the canister.
I think you misunderstood the post. Some pressure is normal, yes. Please watch the video I posted if you need confirmation that this is beyond that amount.
I've watched the video, that is nothing. Can get a lot more volume on a really hot day and a nearly empty tank. Think of the volume of the empty portion of a tank.
You seem very knowledgeable. How do I test the disc valve you speak of. Stands to reason if that was not opening at the .75psi or whatever it is, pressure could build.
Need to put a small amount of pressure on the vapor control valve from the tank side. From the '92 FSM, TBI section: 0.8 - 1.1 psi and the value should open.
what do you recommend I look into here then as the smell definitely isn’t coming from the canister. When I park and smell fuel I have put my face into the canister area and there’s 0 smell coming from it. It smells like it comes from behind you when you pull into the garage. Hence my assumption that I’m smelling the pressure venting out the UFO
It may be from the UFO, it may also be from the gas cap. I've seen a brand new '92 where on a hot day the factory OEM gas cap would not fully tighten and seal the tank.
Could also have a leaking fuel line or a leaking gas tank. Filler neck to tank joint cracked (common issue).
Recall that your OP is about pressure in the tank, NOT excess fumes at the rear of the car...
I am having an issue with signficant pressure released at the gas cap, as well as a fuel smell when parking in my garage. If related, i also have a very hard time getting this car to take fuel from the pump. Ie it stops every 2 dollars or so.
This thread is starting to bounce around a bit. I would go back to post #1 (quote), followed by advice in #2 and #3.
Your first post sounds like an evap system problem. I would completely diagnose that whole system before looking elsewhere.
This thread is starting to bounce around a bit. I would go back to post #1 (quote), followed by advice in #2 and #3.
Your first post sounds like an evap system problem. I would completely diagnose that whole system before looking elsewhere.
And therein lies the problem. We went from too much pressure in the tank, to the presence of fumes at the back of the car.
Watch the video, anyone with a f-body of this vintage will attest that the volume of pressure is minimal. I get that every time I open the cap, cold, hot, lukewarm springtime.
The evap system is SUPPOSED to hold pressure in the tank, full stop.
And therein lies the problem. We went from too much pressure in the tank, to the presence of fumes at the back of the car.
Watch the video, anyone with a f-body of this vintage will attest that the volume of pressure is minimal. I get that every time I open the cap, cold, hot, lukewarm springtime.
The evap system is SUPPOSED to hold pressure in the tank, full stop.
RBob.
I agree. Mine does that. Before when the nylon line was welded shut it would literally blow the gas cap out of my hand and the air blast would be almost 8 seconds long.
And therein lies the problem. We went from too much pressure in the tank, to the presence of fumes at the back of the car.
Watch the video, anyone with a f-body of this vintage will attest that the volume of pressure is minimal. I get that every time I open the cap, cold, hot, lukewarm springtime.
The evap system is SUPPOSED to hold pressure in the tank, full stop.
RBob.
I don’t understand this comment at all. My original post says
“I am having an issue with signficant pressure released at the gas cap, as well as a fuel smell when parking in my garage. If related, i also have a very hard time getting this car to take fuel from the pump. Ie it stops every 2 dollars or so.”
at no point have I bounced from this being my issue except to answer questions asked by others.
Whether correct or not I (and quite a few others who have responded above you here and on plenty of other threads before mine) believe that a non functioning EVAP system could cause excess pressure in the tank. That excess pressure, could certainly smell like fuel from the safety UFO valve.
You seem hellbent on schooling me and everyone else on this board that the tank is supposed to hold pressure. I get it. I understand. My car should not make my garage stink like fuel. I have owned other thirdgens that had pressure, so I won’t say it shouldn’t have any. But none like the one I currently have, none that had issues taking fuel from a pump, and none that made my garage stink of fuel after every drive.
All of this is in my OP. I appreciate your help thus far, but if you have nothing else to add besides “tank should have pressure end of story” than I thank you, and need no more from your expertise here as we are clearly beyond that part of the diagnosis
Last edited by 87irocz28350; 06-25-2024 at 05:50 PM.
This thread is starting to bounce around a bit. I would go back to post #1 (quote), followed by advice in #2 and #3.
Your first post sounds like an evap system problem. I would completely diagnose that whole system before looking elsewhere.
hi thanks. Threads not really bouncing besides other peoples posts. I posted asking if this sounded like an evap problem. Which it does. I posted the test sequence for the evap system from the FSM. I successfully ran the test, and it passed with flying colors.
Now I’m wondering what to do next. Without being derailed by posts trying to tell me there’s no issue with a car with a clear issue, I have been trying my damndest to stay on the topic at hand, as it’s my only issue with this car.
the start of this video the guy literally says that he had pressure and smelt fuel from the back of his car, venting from the UFO, because of excess pressure. I will edit my comment once I finish the rest of the video. But how are we arguing about wether or not there is an issue with my car, and telling me I’m spinning
my wheels or bouncing around by talking about the pressure and the smell, when in the video here that’s the EXACT complaint, followed by the exact hypothesis I have. The excess pressure causes the UFO to vent, as designed, causing smell.
im very grateful for the help from everyone so plz don’t get that twisted I’m just very confused by that sentiment
edit: sounds like from this video he HAD my exact issue, and FIXED it by changing the purge valve which is the circled valve in my 2nd photo of OP. Thanks for this. This may prove to be the most helpful information yet. Much appreciated
Last edited by 87irocz28350; 06-25-2024 at 06:38 PM.
the start of this video the guy literally says that he had pressure and smelt fuel from the back of his car, venting from the UFO, because of excess pressure. I will edit my comment once I finish the rest of the video. But how are we arguing about wether or not there is an issue with my car, and telling me I’m spinning
my wheels or bouncing around by talking about the pressure and the smell, when in the video here that’s the EXACT complaint, followed by the exact hypothesis I have. The excess pressure causes the UFO to vent, as designed, causing smell.
im very grateful for the help from everyone so plz don’t get that twisted I’m just very confused by that sentiment
edit: sounds like from this video he HAD my exact issue, and FIXED it by changing the purge valve which is the circled valve in my 2nd photo of OP. Thanks for this. This may prove to be the most helpful information yet. Much appreciated
I think I said it before but check that nylon control line, it's referred to in the video. It's the one that goes under the TB. If it's burnt or welded shut from the heat, that entire system is shut down. That's what happened to mine.
I think I said it before but check that nylon control line, it's referred to in the video. It's the one that goes under the TB. If it's burnt or welded shut from the heat, that entire system is shut down. That's what happened to mine.
thanks. Will do. Is this the one that feeds the vacuum to this?, it routes under the air cleaner and all.
This might be dumb, but take out the air cleaner to see it right ?
thanks. Will do. Is this the one that feeds the vacuum to this?, it routes under the air cleaner and all.
This might be dumb, but take out the air cleaner to see it right ?
Are you TPI or TB, I may have missed that part. Either way I think it's the same idea. It's a small vacuum line. You can just trace it back to the source and make sure it's sound.
Are you TPI or TB, I may have missed that part. Either way I think it's the same idea. It's a small vacuum line. You can just trace it back to the source and make sure it's sound.
TBI. So again this is the vacuum line that feeds the evap canister? Yeah?
Yes. It's the vacuum line that controls the canister. Not the one that pulls the vapor
sorry one last question. This confused me haha.
I have one vacuum line. It runs to the solenoid ontop of the canister.
im not sure what you mean by “the one that pulls the vapor” perhaps you mean the vacuum line that feeds the purge solenoid but on my setup that’s just Ted off the from same line going from tank to canister (which is the solenoid I’m replacing) see picture 2 in my original post
Last edited by 87irocz28350; 06-26-2024 at 01:12 PM.
I have one vacuum line. It runs to the solenoid ontop of the canister.
im not sure what you mean by “the one that pulls the vapor” perhaps you mean the vacuum line that feeds the purge solenoid but on my setup that’s just Ted off the from same line going from tank to canister (which is the solenoid I’m replacing)
Your can is different that the TPI ones. Looks like the smaller line that goes to the solenoid in your picture is the one you want to verify.
I think the difference is in the year, VS the TPI/TBI.
pre 89? was vacuum controlled canister and mine is (I believe so far) ECM activated but still vacuum controlled
thanks for ur time
No worries. It's ECM controlled but that small line is controlled by the ECM. Mine was burnt and welded shut so when the ECM called for it to open, nothing happened. I chased that issue for years. And my gas cap would blow itself out of my hand. It was a grenade every time I had to fill the tank.
Is this purge valve a one way valve? By that I mean, does it only flow one way, from the tank to the charcoal canister? The little tube on top is actuated by vacuum.
Is this purge valve a one way valve? By that I mean, does it only flow one way, from the tank to the charcoal canister? The little tube on top is actuated by vacuum.
that is my understanding and also that it’s not unheard of for them to be stuck closed a.k.a. nothing making it from tank to canister even when commanded open. My new one arrives tomorrow. I’m hoping that this fixes my issue.
that is my understanding and also that it’s not unheard of for them to be stuck closed a.k.a. nothing making it from tank to canister even when commanded open. My new one arrives tomorrow. I’m hoping that this fixes my issue.
06-19-2024, 02:56 PM
