Does your garage smell of gas after a ride?

Last update: 1/18/10
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After taking a ride and parking the car I would notice a strong smell of gasoline in my garage a few hours later. I found and fixed a few small seepages in my fuel system but could never get rid of the really strong smell that started a few hours after a ride.

It was so bad that I was leery of flipping the garage light switch ON.  After a few days the smell would more or less go away.

Source of problem
As you might have suspected the source of the smell was due to my vented fuel cell. Why it only occurred after a ride and didn't smell as soon as I parked the car is somewhat of a mystery. I suspect that since the boot ("trunk") isn't covered that the fuel cell itself was getting warmed by the sun while I was driving around and it took awhile for the heat to cause the fuel to evaporate enough that I could start to smell it.  (I'm still investigating where my gas goes when I'm NOT driving the car.  I think I've found that there is still a leak (about 1 qt. per month) when the fuel pressure is below 20 psi or so.  Gory details will be forthcoming once I find/cure the problem.)

The gas smell solution was actually rather simple.  Install an fuel evaporator canister system.

How does a charcoal canister gas fume trapping system work?
In case you aren't familiar with how these things work, here is a simplified description of the operation.

Older cars without emission controls used what's called a "vented" gas tank. i.e. the filler cap usually had a small vent in it so air could enter the gas tank to replace the fuel as it was used. On the other hand, gas vapors could escape through the vent and smell. This is similar to a lawn mower fuel system still used now days.

Cars designed to meet emission requirements  use a "sealed" gas tank so it is not able to vent gas fumes directly out of the tank to the surrounding air. A vent tube is provided to vent the fumes into the evaporator canister.  The fuel tank also has a liquid separator so raw fuel can't be vented through the vent tube. The separator may be built into the tank or can be external to the tank. The mass of hoses/pipes you see around some fuel tanks are usually part of the fuel separator system.

A canister which has activated charcoal pellets in it is used to temporarily absorb and store the gas fumes. When the engine is running the canister is connected by various hoses and valves to a source of vacuum from the engine to draw fresh air through the canister. This causes the charcoal pellets to give up the gas fumes which are normally drawn into the engine intake system. This drawing of the air through the charcoal pellets in the canister is called "purging" the system.

On the first generation of using the canisters, car and truck manufacturers sometimes just used an arrangement that allowed the intake system to constantly purge the canister. A restriction was placed in the vacuum line to the canister to limit the amount of air bled into the intake system. This vacuum leak could cause various problems including stumbling on take off etc.

Modern cars with fuel injection use the ECU (Engine Control Unit) to not only manage the fuel injection, ignition, etc but it also control the purge cycle. These systems work very well and don't cause any engine problems.

Various methods are used to limit when the purge takes place. These include water temperature sensors, the ECU can sense the speed of the engine etc etc.

Considerations in using a fuel evaporator canister on a Locost:
If your donor car includes a fuel evaporator canister system, I'd transfer the whole system to your car. It doesn't add much weight and the purge actually allows you to burn ALL the gas (including the fumes) that you buy.

Most Locost builders are going for simplicity and probably aren't going to have a fuel separator. You can simulate the separator by mounting the canister so the top is an inch or so above the top of your filler vent. And don't overfill your tank.

The main problem is how to control the "purge" cycle timing.

Basically you can connect a hose to a vacuum port on the intake system and run it to the canister. Somewhere in the hose between the intake system and the canister you should have a restriction to limit the amount of air/fumes drawn into the intake system. A small solid connecting tube with a 1/32" air passage through it would be a starting point. I'd just solder a small copper tube full of lead and then drill the small hole through the solder.

When you use a motorcycle engine there might not even be vacuum ports on the intake. Later model California fuel injected motorcycles DO have evaporator canisters installed and do purge properly. If you have one of those engines you only need to get the system working properly with the sealed gas tank you now use. If you have a non-CA bike engine you will have to improvise a vacuum system.

Where I got the vacuum on my BEC for the purge:
On my Suzuki GSXR-1000 engine there is an emission system called "PAIR". PAIR is a form of exhaust pipe air injection system. Other motorcycles may have a similar system. On the first generation automotive emission systems an air pump was used to supply the air.

The Suzuki PAIR system uses the vacuum that exists for a short time on the exhaust pipe side of the exhaust valve when the valve is first closed. Each exhaust port has a small hole cast/drilled in the head that connects the underside of the exhaust valve to a reed valve that acts to allow the vacuum to pass into a small collection chamber. The chambers are all connected to the actual PAIR valve (controlled by a vacuum port on the #4 throttle body). I used this exhaust induced vacuum as my purge source.

As part of the present engine control unit (ECU) there is a vacuum system that a sensor is connected to. I didn't want to use this system because it would upset the functioning of that sensor. So in my case, it was easier to use the exhaust PAIR system and just burn the gas fumes and not use them to power the car.

I am in the process of installing a Megasquirt ECU to control my fuel injection. Because this system will have a wide band oxygen sensor in the exhaust system downstream from the PAIR system, I can not continue to use the PAIR valve as the purge vacuum source. The oxygen sensor would indicate an incorrect air-fuel ratio because of the fumes or air coming from the carbon canister.

I am in the process of posting articles how I am adapting my car to use the Megasquirt. In one of those articles I describe how I drilled the remaining three throttle bodies to create a second vacuum system for the purge. When I'm finished the Megasquirt ECU will control the purge.

Preparing the fuel tank/cell to be used as a sealed system:
The fuel tank or fuel cell you use needs to be set up so that there is a vent tube that a small rubber hose can be slipped over. This vent tube is connected to the evaporator canister "tank" tube.

Racing fuel cells do not normally have a separator and the "vent" in some may really be a one way valve to allow air to enter the tank but fumes and expanding air in the tank can not escape. A flexible fuel cell can end up looking like it's pregnant if too much pressure builds up inside!   This is not good!

On the Jazz fuel cell that I am using the filler cap has a small circular flexible flap used as the one way (inbound air only) valve inside the "gas cap". I removed it so my cap can pass air/fumes in both directions. I then fabricated a small copper adapter to go from the vent to a rubber hose. This is described under the pictures that follow.

To see an enlarged view of most pictures, left click on a picture or right click and select "View Image".

Pictures and details of how to modify and install the canister system.
Canister side

This is a stock 1990s Honda charcoal evaporator canister from the junk yard.

I found that the Honda units are quite small and have two mounting surfaces on them. This allows you to select the mount that angles the tubes that are best for your installation.

You also need to get the metal mount and the bottom vent tube (not shown). At the bottom a piece of  1" diameter air vent tube about 6" long is used to keep dirt and water out of the canister.

Canister top

This is the top view of the canister. The tube in the center is connected to the fuel tank.

The top of the small round area is actually a vacuum operated valve that allows the tube underneath it to draw the fumes from the canister when vacuum is applied to the angled vacuum valve (the tube running off at a 60 degree angle).

This valve will be bypassed and the angled tube can be cut off since it isn't used after the modification..

Purge parts

The purge control valve cover can be removed on the Honda by applying a steady pressure under the outside edge of the cover. It will suddenly pop loose and can be re-installed when the modification is done.

The aluminum looking part is the center of the rubber valve that is next lifted off the top of the canister. Notice which way it is installed so it will seal around the edge when you replace it.

The spring won't be used and can be added to your spring collection. Mine is stainless steel.
Valve mod

Notice that I cut away a small part of the plastic valve seat at the lower end of the purge tube. This allows the tube to be able to draw fumes out of the canister without the purge valve being activated. You could just run a drill down the length of the tube and go through the far wall of the valve seat.

I used a pair of small wire cutters to hack away some of the plastic so the rubber valve could not seat properly when it was re-installed.

Replace the rubber seal and the cover.

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Modification of the canister mount

Mount close

The next thing to make is the actual metal mount for the canister. Once you see how the canister is mounted on the donor car you will recognize this metal piece.

Normally the mount is spot welded to the firewall on Honda cars. This particular mount was a bolt on type from large piece of a car I could not identify. I sawed off the extra metal so this was all that was left of it.

The mount ends up vertical when mounted on tube "W2".
mount drawing

You will have to enlarge this drawing to see it clearly.

I used this drawing to mark my mount when drilling/filing the slots for the hose clamp.

I drilled a line of 1/8" dia. holes between the two dimensioned holes on each angled line and then used a small file to finish the slots.

I spray painted it black when I was done filing.
Mount side

This another view of the mount showing how I shaped the hose clamp to go around tube "W2".

The clamp sides are actually 1" apart to account for the thickness of the rubber that I wrapped around the tube .

I don't like to drill holes in frame tubes!

Here is the finished mount on tube "W2". I wrapped two turns of inner tube around the tube to help hold the mount in position.

The canister is just pushed down into the "V" groove which holds it in place.

The mount is positioned vertically.

Canister finished

I've mounted the charcoal canister onto the mount in this picture. You can see the other mounting area on the canister that I didn't use.

The hose on the left goes through a 2 way valve to the tank vent (picture shown later). I added the 2 way valve after this picture was taken.

Notice that the hose is routed higher than the top of the canister. This is done to keep any liquid fuel out of the canister.

The hose from the right side of the canister goes to the PAIR valve (the next picture describes the PAIR valve) at the front of the car.

The small orange one way check valve was later moved to the front of the car to use the volume of the green tube to smooth out the vacuum pulses coming from the PAIR valve.

There is a ~1/2" diameter "vent" tube connected to the bottom of the canister that is open to the air. During the purge, fresh air is drawn into the canister through this hose.
PAIR valve

This is the Suzuki GSXR-1000 PAIR valve system. Each square cover has two one way reed (check) valves that only allow the vacuum under the exhaust valves to pass to the PAIR valve. The round object between the two covers is the vacuum operated PAIR control valve.

The smaller "U" shaped hose connects to #4 intake throttle body and has vacuum on it when the engine is running. The engine vacuum controls the PAIR valve operation but doesn't lean out the fuel mixture to #4 cylinder in the process.

The PAIR valve routes the exhaust vacuum to the medium sized hose at the top of the valve. This hose connects to the front end of the green vacuum purge hose. The other end of the green hose connects to the  tube on the evaporation canister at the back of the car.

The orange check valve in the previous picture is now connected in line to the upper hose just out of camera view. It is positioned so air can flow through it towards the PAIR valve.

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Modification of the Jazz fuel cell cap

Jazz vent

This is the stock Jazz fuel cell filler cap.

The vent is located under the small metal cover at the 11 o'clock position.

If your cap is hard to remove, try rotating it to each of the 120� positions. I found that it was much easier to remove the cap at one of other positions. It also helps to file the metal tabs of the cap so they are a little shorter.
Jazz pin

This is the cap with the metal cover removed. The four small holes are the actual vent(s).

Notice that I have started to remove the metal pin that holds the cap parts together. The pin can be started out of the levered handle with a paper clip.

Vent rubber

 This is the underside of the filler cap once the locking mechanism has been removed.

Note the circular rubber valve at the 10 o'clock position.

The cavity in the cap serves as a (very) small fuel separator.
Jazz rubber removed

Just get your finger nail or a thin screwdriver tip under the rubber edge, lift the rubber up and gently pull the valve out of the plastic cover.

The four vent holes are now open to the outside world.   Air can flow in and gas fumes can flow out to the evaporator system.
Vent tube

This is the new vent cover I made that goes on the outside of the filler cap.

It is made from a 1/2" plumbing copper tube "end cap". I drilled a small hole horizontally near the top and soldered in the small vent tube. The hole in the center is counter sunk for the new #12-32 thread flat head screw that holds the assembly onto the fuel cap.
Vent parts

Also shown here is the rubber gasket made from a piece of inner tube. It fits around the raised part where the four vent holes are. It has a large enough diameter so the 1/2" cover rests on the rubber which seals the system.

The countersunk screw will seal onto the copper end cap due to the smooth surfaces.

Vent new

Here is the new sealed vent assembly on the filler cap.

The hose goes to the "Tank" port on the 2 way valve. Try to mount the 2 way valve as high as possible to keep liquid gas from reaching the charcoal canister.

There is a description of the 2 way valve in the next section.
Tank done

Here's all the hoses connected up. While it's hard to see in this picture, the top of the 2 way valve is about 3" above the fuel cap.

The vent hose is routed so the highest point is ~4" above the tank. This hopefully will keep liquid gas from entering the canister.

There is a description of all the labeled items at
How to modify the GSXR Suzuki fuel pump for a fuel cell

Does it work?
But of course!

After the first short ride around the block I had a strange new smell in the garage. Not quite gas, but definitely a musty petroleum product smell that I didn't have before.

After thinking about it for awhile I realized that the stale gas fumes from the Honda car in the junk yard had probably saturated the canister and the vapors in my fuel cell were pushing them out the bottom vent of the canister.

I took the car for a longer ride and that ended all the smells. Now I can turn the garage light ON without hiding behind the door.   ;-)

After a few weeks I again started noticing a very faint smell of gas now and then several hours after a ride. It seems  that I have a strange situation of a slow seepage/leak that only happens when the fuel pressure in the gas line is below 20 psi or so. I'm investigating that now.

(I later found a small seepage at one of the fuel line clamps.)

4/22/09 update:
Once in awhile I -still- smelled a faint whiff of gas fumes so I installed a "2 way valve" from a 1989 Honda CRX . This valve is placed in line with the hose from the fuel tank vent and the canister. It allows fresh air through the canister to enter the fuel tank with very little restriction but causes the fuel vapors in the fuel tank to build a little pressure (probably on the order of a lb or so) before they are vented into the canister.

This helps to not saturate the canister with fuel fumes.  The addition of this valve has gotten rid of the last bit of fuel smell I was having.

On a Honda CRX  the 2 way valve is located on the left side of the car just in front of the rear tire area. I suspect that other Honda Civics etc will have the same valve.

After you remove the left rear tire, look under the car towards the front of the fender well opening and you will see a plastic cover that has to be removed. Once that cover is removed (no easy task in itself) look near the right side of the fuel pump for a circular disk with two small hoses connected to it. That's the 2 way valve.

It's not the easiest thing to get at but it was worth the time to remove it from the car.

The next two pictures show the 2-way valve after it was mounted on my car.
2 way left

This is the left side of the 2-way valve. The hose connected to the red cover goes to the vent on the fuel cell.

On the left side of the 2 way valve you can see the short piece of aluminum angle that is used as the mount for the valve.

There is the word "Tank" cast onto the red cover. Make sure you don't connect the hoses in reversed order!
2 way right

This picture shows the right side of the 2-way valve and how it is connected to the canister. The short black hose goes to the tube on the canister that used to go to the vent on the fuel cell.

In affect the 2 way valve is connected in series with the vent hose from the fuel and the canister.

The short hose also cushions the 2 way valve so it doesn't vibrate or move around on the somewhat flimsy aluminum mounting bracket I made.