The canister is sized according to or relative to the volume of the fuel tank. The larger the fuel tank, the larger the vapor canister. It is about capturing the gasoline vapor (as the ambient temperature and road/parking lot temperature increases, causing the gas tank to heat up and vaporize the gas) and holding it till you start the engine. The PCM, ECM then allows engine vacuum to purge the canister of raw gasoline vapor and NOT allow it to vent to the atmosphere. Your little canister is not properly sized for the fuel tank of the Fiero. Thus, raw vapor will vent to the atmosphere.
I'm trying to wrap my head around what is going on in this system. It is a closed system, so flow can't be too much. The whole purpose of the system, as I understand it, is to allow for expansion and contraction due to temperature changes and to prevent a vacuum to form as fuel is used in a closed system. That is about 4 or 5 liters of air displaced every 30 minutes . If all it is doing is absorbing fuel vapors from air, that isn't much fuel, or am I missing something?
As others have chimed in and pointed out, a lot of expansion takes place in the tank. Another observation I made that clued me into the vent line being plugged, was the occasional crumple sound the tank would make as those gases expanded and were released upon removal of the cap and an important other point that was pointed out above, is canister saturation. This is general information that some have learned the hard way; When the gas pump handle automatically shuts off indicating the tank is full on modern cars, STOP filling. Trying to top off the tank further can result in fuel saturating and ruining the canister, which more often than not, is located on top of the fuel tank, which can be a very expensive repair for those who need, or want the engine light off after startup. The EVAP solenoid is a commonly failing part on modern GM cars and when replacing it doesn't clear an EVAP code, it usually means there's trouble at the canister.
Look up a simple EVAP diagram on how the system works for more insight.
[This message has been edited by Joseph Upson (edited 07-30-2020).]
Here is a good video that shows all the components, and how they work Take a look at that canister and how much active charcoal is in here. I have this link set to start at this point, but this guy goes into detail throughout the whole system. Hope this helps to get your head around it. I would find a place to add in the canister from the donor car, or possibly replace the Fiero expansion tank with the modern canister. The Fiero expansion tank is doing only part of the job these charcoal canisters are designed to do in more modern systems.
So the take-away is that a charcoal canister that is too small will not have the charcoal surface capacity to absorb sufficient vapors, resulting in vapors being released into the atmosphere?
So the take-away is that a charcoal canister that is too small will not have the charcoal surface capacity to absorb sufficient vapors, resulting in vapors being released into the atmosphere?
Yes. It is also true that raw fuel vapor is the most harmful to the atmosphere. Nothing that comes out of the tailpipe is worse except for the unburned fuel. But I am not getting all tree hugger on you, any raw fuel vented out can smell awful in a garage and may even be hazardous.
[This message has been edited by Rickady88GT (edited 07-30-2020).]
So the take-away is that a charcoal canister that is too small will not have the charcoal surface capacity to absorb sufficient vapors, resulting in vapors being released into the atmosphere?
A fuel tank isn't a closed system; if it were closed, you wouldn't need a charcoal canister. No vapours could escape.
To avoid pressure buildup, a fuel tank is vented to the atmosphere. Naturally, this causes fuel vapours to escape via the vent. In modern cars, a charcoal canister is placed inline with the vent line, to adsorb the fuel vapours. The air continues to pass freely through the canister, equalizing the pressure with the outside.
At some time when the engine is running, the canister will be purged of fuel it had adsorbed. The engine will suck gasoline-laden air from the canister, removing gasoline from the charcoal.
Now that the charcoal has been purged of gasoline, it is ready to again adsorb fuel vapour the next time the car is parked.
The gasoline is adsorbed onto the surface of the charcoal granules.
The gasoline is not absorbed inside the bulk of the granules.
Ok, but exactly where is the vent to the atmosphere? Here is my issue. The original canister has a "soft bottom" . I assume that is where it vents through. On the original car configuration, the purge seems to be controlled by engine vacuum with a diaphragm on the top of the canister. Also, in the original configurations, the tank vent is 3/4" and goes directly from the tank to the top of the filler neck. This means that vapors, during filling of the tank, exit to the atmosphere without being absorbed because the canister is not in play when fueling. The swap engine I am using is a 2013 impala 3.6l. On that car, the canister purge is controlled by the ecm and an electrically operated purge valve. The impala canister does not have a vent. I assume the vent is elsewhere in that system. It seems to me that neither the Fiero canister nor the impala canister will operate properly on my swapped car unless I modify the canister or ad a vent somewhere.
Since the introduction of OBD-II, you can't just vent the canister with a simple hole.
OBD-II requires the system be regularly pressure-tested to detect any leaks, which could allow for fuel vapour to escape.
Now there's normally a solenoid inline with the canister vent. When the ECU decides to test the system for leaks, it will (temporarily) close the vent solenoid, and see if pressure builds up.
Since the introduction of OBD-II, you can't just vent the canister with a simple hole.
OBD-II requires the system be regularly pressure-tested to detect any leaks, which could allow for fuel vapour to escape.
Now there's normally a solenoid inline with the canister vent. When the ECU decides to test the system for leaks, it will (temporarily) close the vent solenoid, and see if pressure builds up.
So how does the vapor get vented? Isn't the whole idea to prevent pressure build up in the fuel tank when the ignition is off? Is vapor routed through the canister, removing fuel vapor from air, then allowed into the atmosphere? Isn't that how the Fiero canister works?
not wanting to start a fight, but, I have an LS3 in my 88 coupe. I went to Archies to have it installed and even helped out with the install a little. One thing I remember is that we removed the expansion tank that sits above the pass rear wheel and the charcoal canister that was in the engine bay. The gas tank now vents thru the metal line/hose that led to the charcoal canister and i put a small air cleaner on it. I smell no "excess" gas coming out of it and have had no issues driving the car this way for 7 years. Yes I understand its not helping the environment venting the gas tank to the air, but from a driving point of view removing it does not seem to have effected the engine at all. Another guy in my local club has the same setup and he routed the line on his to a homemade charcoal tank made from some lawn sprinkler parts. It seems to work and it looks really cool.
For me, this is more a learning thing. The original Fiero setup is different from the setup on the 2013 impala. Making a hybrid of the two is interesting to me. It would be easier if I had a sketch of the Impala system.
Originally posted by Daryl M: Isn't the whole idea to prevent pressure build up in the fuel tank when the ignition is off?
Yes, we don't want the tank to become inflated.
quote
Originally posted by Daryl M: Is vapor routed through the canister, removing fuel vapor from air, then allowed into the atmosphere?
Yes
quote
Originally posted by Daryl M: Isn't that how the Fiero canister works?
Yes again.
With OBD-II, I suppose that vent solenoid is closed only long enough for the leak test to be performed. I don't think the pressure is held in long enough to cause problems. I don't know the specifics.
Sometimes, on an OBD-II car, when you unscrew the gas cap, you can hear a hiss.
[This message has been edited by pmbrunelle (edited 08-01-2020).]
With OBD-II, I suppose that vent solenoid is closed only long enough for the leak test to be performed. I don't think the pressure is held in long enough to cause problems. I don't know the specifics.
Sometimes, on an OBD-II car, when you unscrew the gas cap, you can hear a hiss.
Thanks for all of the good info. I'm learning a lot.
After more research I found a vapor canister that has a vent solenoid incorporated in the canister. It fits several 2012-2015 GM cars like the Buick Verano and Chevy Cruze, etc . Does anyone know if the vent solenoid is normally open or normally closed?
After more research I found a vapor canister that has a vent solenoid incorporated in the canister. It fits several 2012-2015 GM cars like the Buick Verano and Chevy Cruze, etc . Does anyone know if the vent solenoid is normally open or normally closed?
They should be failsafe. On the newer cars they have a purge and vent solenoid. If the battery goes dead, or the car is not run for extended times, the tank must still be allowed to let the gas expand and contract. The solenoids work to suck the fuel vapor out of the canister.
I recieved the Verano canister today. I checked and the vent solenoid is normally open, so I'm planning on wiring the vent solenoid to an ignition hot wire, so it is closed when the car is running and open when the car is not running. Does anyone see problems with this plan?
[This message has been edited by Daryl M (edited 08-05-2020).]
You're sure the Impala doesn't have a vent solenoid, somewhere? What does the Impala do to vent its canister?
Modern cars/ECUs are control freaks; take away something from their grasp, and they may throw a check engine light back at you.
Yes it does, but the ecm I am using has been modified to delete that function. Many functions were deleted so the ecm could be used as a stand alone with a manual transmission.
If your ECU doesn't do the leak test, then you never need to close the vent solenoid to test for leaks (by checking for pressure buildup). In that case, you don't need a vent solenoid at all.
I think that keeping the vent solenoid closed at all times during engine operation would cause a problem with purging. When you try to purge the canister, the engine won't be able to suck vapour from the canister if it's sucking from a dead-end. The vent would need to be open to get air to flow through the canister, pick up fuel vapours, and then be sucked into the engine.
[This message has been edited by pmbrunelle (edited 08-05-2020).]
If your ECU doesn't do the leak test, then you never need to close the vent solenoid to test for leaks (by checking for pressure buildup). In that case, you don't need a vent solenoid at all.
I think that keeping the vent solenoid closed at all times during engine operation would cause a problem with purging. When you try to purge the canister, the engine won't be able to suck vapour from the canister if it's sucking from a dead-end. The vent would need to be open to get air to flow through the canister, pick up fuel vapours, and then be sucked into the engine.
In that case, couldn't I wire it in tandem with the purge valve solenoid?
Yes it does, but the ecm I am using has been modified to delete that function. Many functions were deleted so the ecm could be used as a stand alone with a manual transmission.
You will not likely know the extent of the effectiveness of the changes to the programming until the system is up and running. Their are changes within changes to the modern PCMs in use, like the advent of global A which I understand has caused some tuning problems with swaps. More importantly, some functions are hard wired into the programming, particularly in the emissions department, where although a particular code has been turned off, it still reports in some way, for instance, disabling the EVAP code in some cases, may not ever set a code in the PCM, but I understand it will never show the test as having been completed also, which could set a red flag for someone needing it to register.
There's also the possibility that some other function may be disrupted as these systems are vast and it's very likely not many of the platform you are using have been used outside of their OE setting to know what problems may show up in a case like yours. The Fiero is probably the most transplanted car around so unknown problems may show up here. This info is from problems I've read about in more commonly modded platforms, particularly the Camaro. If the provider that made the changes to your PCM is applying a general approach used elsewhere, while at the same time having had little experience with your transplant vehicle due to low demand, you might be in for surprises. I'd set it up stock to minimize the potential for trouble.
When the purge valve is on (either ECU-controlled or hot-in-run), the vent needs to be open. When the purge valve is off (engine off), the vent needs to be open.
If you don't perform the leak test, the vent never needs to close, and as such a vent is not needed in this situation.
Another more "hard-wired" idea would be to set the purge valve to be hot-in-run, if your computer doesn"t control the purge valve anymore (this is not clear from your posts).
Purging all the time (including at idle) may be contraindicated however.
In a stock Fiero, purging occurs any time when ported vacuum exists. So at idle, the vacuum leak (containing unknown amounts of fuel) from the charcoal canister is closed, preventing it from screwing around with the idle mixture.
At greater loads, I think the variability introduced from the charcoal canister is less of a problem.
You could just try to get the Fiero canister working. It only needs two vacuum lines to work: 1 manifold vacuum line 1 ported vacuum line (may need to drill the throttle body for this)
When the purge valve is on (either ECU-controlled or hot-in-run), the vent needs to be open. When the purge valve is off (engine off), the vent needs to be open.
If you don't perform the leak test, the vent never needs to close, and as such a vent is not needed in this situation.
Another more "hard-wired" idea would be to set the purge valve to be hot-in-run, if your computer doesn"t control the purge valve anymore (this is not clear from your posts).
Purging all the time (including at idle) may be contraindicated however.
In a stock Fiero, purging occurs any time when ported vacuum exists. So at idle, the vacuum leak (containing unknown amounts of fuel) from the charcoal canister is closed, preventing it from screwing around with the idle mixture.
At greater loads, I think the variability introduced from the charcoal canister is less of a problem.
You could just try to get the Fiero canister working. It only needs two vacuum lines to work: 1 manifold vacuum line 1 ported vacuum line (may need to drill the throttle body for this)
It's a really simple non-computer setup.
The purge valve is still controlled by the ecm, according to the documentation I was given by the tuner. I may have not been clear about planning to wire the vent solenoid to the purge valve control circuit. I plan on using a relay in order to de-energise the vent solenoid when the purge valve is opened, and vice versa. Shouldn't that accomplish the goal of opening the vent when the purge valve is open and closing the vent when the purge valve is closed, while leaving the vent open when the ignition is off? Shouldn't that work?
Where did you order it from? Maker? Cores? Size? Depth? hp rating?
Does it sit in the lower pocket without modification or will you have to perform some BFH enhancements? (Edit: looks like the intake hose bung hits the pocket sheet metal...
Obviously you'll have to fab up some custom top and side mounts...
I'm not quite to this point yet, but it's coming very soon on the docket...
[This message has been edited by msweldon (edited 08-08-2020).]
It is a Northern Radiator kit #209663B I found on Ebay. The seller is a shop in Minnesota, Dillon Radiator. They finished it to my specs and sent it to me. Below is the manufacturer's site with specs. https://www.northernradiato..._ROW/16_INCH/209663B
This is where my evap canister ended up. It originally fits several later models from GM including the Buick Verano and Chevy Cruz., and now a Pontiac Fiero with an LFX.
Getting back to the radiator, what pressure cap should I use? The Impala donor car uses a 20 psi, but Fieros are significantly less than that. Any thoughts?
Modern cars use higher cooling system pressures to mitigate nucleating bubbles from micro-boiling events in the cylinder head cooling jackets. The cooling jackets in modern engines are pretty thin to promote quick warm up and require pretty high flow speed in order to carry enough heat away from the engine metal. Some micro-boiling is planned in, as the latent heat of vaporization does an excellent job of cooling. Lower system pressure will allow "more", but whether that's enough more to be more than the coolant flow can move out of the jacket and into the surge tank is a question you'll have to answer with practical experience.
Modern cars use higher cooling system pressures to mitigate nucleating bubbles from micro-boiling events in the cylinder head cooling jackets. The cooling jackets in modern engines are pretty thin to promote quick warm up and require pretty high flow speed in order to carry enough heat away from the engine metal. Some micro-boiling is planned in, as the latent heat of vaporization does an excellent job of cooling. Lower system pressure will allow "more", but whether that's enough more to be more than the coolant flow can move out of the jacket and into the surge tank is a question you'll have to answer with practical experience.
Will, if I go with this cap on the reservoir, do I need a cap with a relief valve on the radiator, or do I get a solid cap?
I would find a place to add in the canister from the donor car, or possibly replace the Fiero expansion tank with the modern canister. The Fiero expansion tank is doing only part of the job these charcoal canisters are designed to do in more modern systems.
