Now that it's very hot out here in Vegas, I'm noticing a significant fuel odder. After checking extensively for leaks, and finding none, I started looking at the EVAP charcoal canister on the fire wall. It appears that after a hot drive, the car has a bunch of fumes coming out of the fresh-air intake tube connecting to the bottom of the canister. There is no wet fuel in or around, but I can definitely see wavy fumes wafting out of the tube under the car (I can catch them with my hand). I always thought that was tube was ONLY a fresh air intake (one way) and that fumes should not be able to come out this way. Does anyone know how to fix this?

94 Civic CX
B18C swap
No liquid leaks
No loss of mpgs
No loss of performance

***EDIT 08-02-2017*** Solved!!!! see post #10 below

 

extend the hose so it vents further under the car. I ripped mine out completely and plugged the vent line to the tank but that's my situation. extending/rerouting the hose should work for you unless there is a crank on the can it's self.

 

The stock hose extends pretty far under the car as it is. This is a new problem on a 20yr old car. I would think something must not be functioning correctly.

 

For those that search this problem in the future I found the following link. Another person in Las Vegas had the exact same symptoms as I did with his 92 Accord (now I have it on two cars 94 Civic & 89 CRX). The problem seems to point at the EVAP 2-way valve on the fuel tank. I popped mine off the 94 Civic and cleaned it out with some QD electronics spray cleaner (safe for rubber & plastic). Seems to help with the 1st warmer day. We'll see when I drive it Tomorrow as it will be ~105 outside.

This valve is on the side of your fuel tank underneath a plastic cover. It is accessible from under the car without dropping the tank EGs & EFs. I'm not expecting much by simply cleaning the valve. Replacing it is only about $40, so I may go that route next.

http://www.justanswer.com/honda/2hhr...las-vegas.html

#2 in the following pic:

 

Thanks for the update.

 

Cleaning the 2-way valve has not changed anything on the EG.

My next option is to swap in a larger OBD1 charcoal canister. EX EG's & some Del Sol B16's came with the same larger ToyoRoki brand canister found in all 94-95 Integras. My 94 CX came with the smaller Tennex brand canister, and I have a feeling it might just be getting overwhelmed. Who knows. I have a used Toyoroki on the way right now.

Should be here in a day or two, and I'll report back once I try it out. If it works on the EG, perhaps there is a way to adapt one of these canisters to the EF.

Toyoroki 90B73Q canister 1.3 lbs


Tennex TWV76A canister 1.0 lbs

 

Got both canisters out and measured them for reference....

Tennex: 533 grams
Toyoroki: 628 grams

I'm really hoping this helps. When I run the AC, this car gets pretty stinky at the stoplight. I'll report back tomorrow.

 

Okay beefier canister didn't help. Smells exactly the same. Glad I only wasted $15.

I'm pretty sure it's the 2-way valve then. I'm guessing it's not opening soon enough, thereby causing too much pressure inside the gas tank. Then when the valve finally blows open, so much vapor comes out all at once, it overwhelms the charcoal canister with fumes before the throttle-body can consume them via the purge hose.

I disconnected the evap hose from the throttle body, and there really is very very little draw from the motor (on both cars). When you pop it off there is no audible hiss (over the normal motor noise) and no change in idle from an open vacuum source. I guess this system is supposed to draw from the charcoal canister quite slowly.

I'm wondering if years of me topping off the fuel tanks (they say don't do that) has finally caused me problems with these two-way valves.

 

Just to update.....My findings after talking with the Honda shop foreman are that this can be quite normal in the summer. It's the very reason the government mandated sealed EVAP systems in 1998. The system simply gets overwhelmed in high heat of summer and cannot flow enough of the fumes into the throttlebody to keep them from escaping via the fresh air vent.

We'll see how bad it is again as it gets hot out here.

***EDIT: Changed 1996 to 1998. That's when Honda added the "Vent shut" solenoid to the charcoal canister to control the flow of fresh air and prevent fumes escaping. 1996 was the year Honda changed the canisters (in North America) to use direct manifold vacuum to purge the canister (instead of the weak passive draw from the throttle body nipple found on 1995 and earlier). The 96-97 canister still had an open/unregulated fresh air port.

 

Solved!!!!

So this summer (2017) the gas smell was getting worse and worse. It was happening at lower ambient temperature both with and without AC operation. I took apart the EVAP system and attempted to clean the pipes out. I even bought a new 2-way valve thinking the old one may have been building too much tank pressure and blowing out too many fumes at once. Nope!

In the end getting a new OEM charcoal canister was the answer. Apparently if you top off your gas tank (which I always did since 1999), you run the risk of fowling your charcoal canister with liquid fuel. Over time, either the capacity or flow of the canister is reduced (not sure which). Since installing the new OEM canister, I haven't had any fuel smell whatsoever. Fortunately the TENNEX canister for my 94 CX was still available through Honda for about $60. They still have some left too at this time (I think about 30). The only other EG canister I could find that was still available was from the 95 EX Sedan. For some reason different years & trims have different part numbers. But I have a feeling they are all interchangeable with a little effort. Even the one I recieved was a little different from my original one (the port on the bottom was different angle).

DO NOT TOP OFF YOUR FUEL TANK!!!!

 

I may need to look into this. My 2000 LS does this on very hot days.

 

Good info! I get this from time to time as well, gonna have to price out a canister for then DB.

 

Great info.

Isn't this a similar problem to what 94 Civic Si was experiencing?

 

Good info. I'll wait for it to click from now on. the obd1 canisters are what I need for my specific ecu/engine setup anyways.

 

His was a little different. He was blowing gas fumes because he had an OBD2 EVAP solenoid hooked up to an OBD1 ECU. Those two systems work in exact opposite ways. This caused his EVAP flow to the engine to close once the engine was up to temp (which eventually overflows the canister of fumes from normal fuel heating).

My system was hooked up correctly (OBD1 solenoid w/ OBD1 ECU), but my canisters had no capacity to contain fumes I guess.

I did purchase parts and try his setup on my car (OBD2 solenoid & canister w/ OBD1 ECU) but found the exact same problems he had.....vacuum leak when cold....no evap flow when warm.

 

That is awesome news! And yes, wetting the charcoal media in the can will ruin it. You are lucky $60 was the price. Other vehicles are a lot more, w/ no aftermarket options...

I know some folks have tried cutting open the can and replacing the charcoal with charcoal used for fish tank air filters.

Any chance you want to cut your old can open and show us what the media looks like?

Good memory mate!

Yep! Now I have the purge diaphragm hooked direct to manifold vacuum (bypassing the OBD2 solenoid) so there is vacuum on the diaphragm any time the engine is on. The purge line is connected to my throttle body so vacuum is purging the can any time engine speed is above idle.

This works great - no gas smell in the cabin, no stumbling idle.

Thanks for figuring out these key differences for me!

Now all I need to do is figure out why my IAB is not functioning to give me long runners below ~5200 RPM.