Persistent gasoline smell from my MK4 - Solved!

[lgordon]

I’m trying to chase down a fuel smell coming from my MK4 and would really appreciate some advise!

When I was at go cart stage with a few gallons of fuel in the tank neither my wife or I noticed any gasoline smell in my garage. A few weeks after my car was complete, except for getting it registered, I filled the tank and started smelling gasoline, especially strong when it sat in my closed garage overnight. It’s coming from somewhere near the gas tank but I can’t specifically locate from where. I can’t spot any leaks either at the tank or any of the fuel pluming. I also checked around the sender and fuel pump hanger covers, nothing. The smell is essentially unchanged now that I’ve driven a bit and the tank is only 3/4 full.

I tried changing the filler tube gasket at the tank. I took the precaution of first siphoning out 5 gallons of fuel so it wouldn’t spill on the floor. I used engine oil to lubricate both the new Ford OEM gasket ( F4ZZ-9072-DA) I bought and the filler tube before inserting. I have the fuel filler tube inserted in the tank so that the rolled bead is about 1” away from the tank. That allowed me to have the filler tube fairly straight and visually centered in the gasket with no apparent distortion. At first that seemed to solve the problem but when I put the 5 gallons of gasoline back in the tank the smell came right back.

I siphoned 5 gallons out again two days ago and have kept my garage closed since then. Even my wife with her more sensitive nose can’t smell any gasoline aroma now, with the tank less than half full.

At this point I can only think of two possibilities. 1) The alignment of the fuel filler tube might be extremely critical. Even though the filler tube appears to be entering the tank gasket perpendicular to the tank there could be enough angle to comprise the gaskets sealing ability. 2) the other possibility I can think of is that there could be a leak in the weld seam between the upper and lower halves of the fuel tank.

I’m thinking that one way to find out where the leak is would be to use a fluorescent dye in the fuel tank so that I could spot the leak with a black light. One of several brands is: Genuine GM Fluid 88861206 4-in-1 Fluorescent Dye - 1 oz. https://www.amazon.com/dp/B00BK7MDOI/ref=cm_sw_r_cp_tau_2kP2EbDF6TNK6

I was also wondering if a gasket sealer could be used on the filler tube-fuel tank gasket? Such as:
Permatex 85420 Permashield Fuel Resistant Gasket Dressing & Sealant, 2 oz Tube https://www.amazon.com/dp/B007VIGCJW/ref=cm_sw_r_cp_tau_3mP2Eb9F6PVRS

Should I try polishing the fuel filler tube where it goes through the gasket? Just pull the filler tube out again and try to be much fussier about getting the filler tube lined up straight down and perpendicular into the tank?

Any advice would be very much appreciated!

[JohnK]

If it's just a smell of gas and you're not seeing a leak, it's possible that you're just smelling gas vapors escaping from the vent tube. Have you installed a charcoal canister? It's a pretty popular (and cheap and easy) mod that a lot of folks have done, and I plan to do on my build for exactly this reason. A quick search on the forum should turn up how folks have done it. It's likely that you're smelling it more now, since the weather is warming up and the gas in the tank is vaporizing more readily.

[edwardb]

Since you asked, I haven't found the filler tube alignment particularly critical. With the Ford OEM gasket and the tube reasonably straight, I doubt that's the issue. Certainly could be vapor from the vent line and if you don't have a charcoal filter, would be a place to start. I use them and have never had any odor. But others have reported no odor even without the charcoal filter. If the tank were leaking would seem you'd see the evidence plus maybe the level would go down. Although agree it wouldn't take much.

[Big Blocker]

Only four places the tank can leak: the filler tube gasket, the sending unit O-ring, the fuel pump O-ring or the welded seams. You made no mention if you checked the fuel lines at the pump fittings, the vent line, the return line or if you are even running a charcoal filter on the vent. My guess is the non-filtered vent line . . . possibly left open during install.

That being said, In all my years as a FORD mechanic, I have NEVER seen a gas tanks welded seams leak. The filler tube "alignment" is NOT critical at all and can be quite a bit off of 90° perpendicular.

Carbon filters are easily made from PVC pipe and charcoal purchased from a pet store in the fish tank department. There are several posts about how to construct one and get it plumbed into your vent line - gas smell issue solved.

Doc

[BEAR-AvHistory]

Its worth spending the time to build a charcoal canister. Some PVC pipe & end caps + fish-tank charcoal. I use the charcoal filter material that comes in little cloth bags. Open the cap push in the bag & close it up.

[Desert Cobra]

I had a similar problem. Finally traced it down to the fuel level sensor gasket and seal on top of the Mustang gas tank FFR uses on the MK4 kit. Had to drop tank to access it. Still can't fill the tank full but 4/5ths works for me.

[GoDadGo]

Could it be your vent tube?

I ran mine above the tank along the frame which exists on the drivers side.

Instead of having a charcoal canister, I have a plastic fuel filter in the line which controls the air movement.

Fuel smell is minimal at best even without a charcoal canister.

[lgordon]

Thank for the responses! It’s really helpful to know the gasket/filler neck alignment isn’t terribly critical. I’ve already gone to significant effort to make sure it’s well aligned. I have checked the fuel line connections to the pump as well as all other connections in the fuel system. There are no leaks in the pluming, engine running or not. When the tank is mostly full there is always a gasoline smell in my garage.

Twice now I’ve siphoned out 5 gallons of fuel and there is no gasoline oder detectable so long as the tank is less than half full. I’ve run this test running the engine or not after lowering the fuel level. As long as the fuel level is low there is no smell.

Also I do have a carbon canister installed. It’s a canister that came from FFR along with my kit and Coyote/TKO600 package. I’ve attached a photo of the canister. I’ve checked and double checked the fuel vent connections. They are good. The two large openings with plastic screens molded in are open to air. The smaller connection on one side of the top is capped. The slightly larger connection, port, is connected to the tank vent tubing. One thing I’ve noticed is that the side of the canister with the two smaller ports is an empty chamber that about 25% of the canister’s total volume. I’m thinking maybe I should fill that chamber with activated charcoal. Does that make sense?

I didn’t think the amount of fuel vapor being generated inside the tank would be different with a partial vs full tank but maybe I’m wrong.

I’ll try building a PVC pipe carbon canister as other’s have done. Maybe that will work better than the Ford canister.

https://www.partsgeek.com/assets/dimage/fulln/07929120-1140849.jpg

[davekp]

I had a similar problem. Was the sender O-ring, sort of. The lock rings are 3 or 4 tabs. I had a 3 tab trying to work on a 4 tab tank. I think the 4 tab are '94 and '95 mustang. Anyway, the correct lock ring fixed it but I needed a thicker (3/16" I think) o-ring.
Problem solved.

[GThompson]

When you guys put charcoal canisters in do you also hook up a solenoid valve that uses engine vacuum to draw fresh air through the canister to pull the gasoline vapors into the engine to be burned? If not the fuel will eventually saturate the charcoal and you’ll have the fuel smell. I think that the solenoid generally stays open for 10-15 seconds on startup to clear out the fuel.

[j.miller]

Sender O-Ring.

[edwardb]

When you guys put charcoal canisters in do you also hook up a solenoid valve that uses engine vacuum to draw fresh air through the canister to pull the gasoline vapors into the engine to be burned? If not the fuel will eventually saturate the charcoal and you’ll have the fuel smell. I think that the solenoid generally stays open for 10-15 seconds on startup to clear out the fuel.

Haven't seen anyone set one up that way. Modern cars control the purge valve with the ECU. Even the crate Coyote doesn't have that function active or include the valve with the engine. You're right. At some point the charcoal will get saturated and need to be replaced. With the homemade version, it's easy. The aquarium charcoal is cheap. The one in my 20th Anniversary Roadster is in its fourth season with no gas smell. So either it's not saturated yet. Or it's not really doing anything. :confused:

[cnutting]

Had a similar problem, it was the sender o-ring. Gas woud pool in that area if i filled the tank. I had the old style square seals, Tony at FFR sent me o-rings, and that solved the problem.

[dhuff]

Could it be your vent tube?

I ran mine above the tank along the frame which exists on the drivers side.

Instead of having a charcoal canister, I have a plastic fuel filter in the line which controls the air movement.

Fuel smell is minimal at best even without a charcoal canister.

Similarly, my vent is through a crank case filter on the passenger side up as high as possible in the wheel well. Very minimal or no gas smell.

[davekp]

Time to bite the bullet and drop the tank. Since it only happens on a full tank, the issue IS at the sender.

[cnutting]

Before you drop the tank, pop open one of the access panels in the trunk floor, check for residue.

[lgordon]

Does anyone know what the part number / source is for a correct fuel sender O ring? It is time to bite the bullet!

[rich grsc]

Thank for the responses! It’s really helpful to know the gasket/filler neck alignment isn’t terribly critical. I’ve already gone to significant effort to make sure it’s well aligned. I have checked the fuel line connections to the pump as well as all other connections in the fuel system. There are no leaks in the pluming, engine running or not. When the tank is mostly full there is always a gasoline smell in my garage.

Twice now I’ve siphoned out 5 gallons of fuel and there is no gasoline oder detectable so long as the tank is less than half full. I’ve run this test running the engine or not after lowering the fuel level. As long as the fuel level is low there is no smell.

Also I do have a carbon canister installed. It’s a canister that came from FFR along with my kit and Coyote/TKO600 package. I’ve attached a photo of the canister. I’ve checked and double checked the fuel vent connections. They are good. The two large openings with plastic screens molded in are open to air. The smaller connection on one side of the top is capped. The slightly larger connection, port, is connected to the tank vent tubing. One thing I’ve noticed is that the side of the canister with the two smaller ports is an empty chamber that about 25% of the canister’s total volume. I’m thinking maybe I should fill that chamber with activated charcoal. Does that make sense?

I didn’t think the amount of fuel vapor being generated inside the tank would be different with a partial vs full tank but maybe I’m wrong.

I’ll try building a PVC pipe carbon canister as other’s have done. Maybe that will work better than the Ford canister.

https://www.partsgeek.com/assets/dimage/fulln/07929120-1140849.jpg

That's your clue right there. It has to be an o-ring leaking or a faulty fuel tank seam. In fact if it was fuel vapor from the tank vent, it would be worse with a half tank than a full one. I have never used any type of vapor canister and have not had an issue. If you replace the o-rings, be sure to lube them with engine oil and be sure you have the correct locking ring.

[BEAR-AvHistory]

I run a no pollution controls configuration with open breathers on a modified Gen I Coyote crate engine. Legal in NC per NCDMV regulations.

Got 4 years on my homemade canister before it needed changing. When I bought the charcoal it came 3 bags to the box. After some searching finally found the box with the two remaining bags. About 10 minutes to change the bags. Have a year on bag 2, no smell.

FWIW the garage is part of the house but not air-conditioned or heated. During Carolina mid-summer temperatures its quite warm which would accelerate evaporation.

[NAZ]

I thought the smell of gasoline and exhaust fumes were part of the attraction of these cars.

[Norm B]

Haven't seen anyone set one up that way. Modern cars control the purge valve with the ECU. Even the crate Coyote doesn't have that function active or include the valve with the engine. You're right. At some point the charcoal will get saturated and need to be replaced. With the homemade version, it's easy. The aquarium charcoal is cheap. The one in my 20th Anniversary Roadster is in its fourth season with no gas smell. So either it's not saturated yet. Or it's not really doing anything. :confused:

Well now you have. I set up a purge system using parts scavenged from my 95 donor. The charcoal canister is located in the right rear fender next to the filler and a small line runs up to the engine bay. The solenoid valve is activated through a relay by the brake light circuit. When the ignition switch is in run and the brakes are applied the valve opens. I put a restriction in the line between the valve and the manifold vacuum port on the carb (now Sniper unit) to limit the airflow and not overly affect idle speed or tune. I couldn't detect a change in idle with the carb and idle speed doesn't move with the Sniper. The IAC reading does move from 7 to 5% when the brakes are applied at idle. Don't know how much of this is due to the purge air and/or the power brake booster. Never have to worry about the canister getting saturated and the garage smelling like gasoline.

Norm

[davekp]

Does anyone know what the part number / source is for a correct fuel sender O ring? It is time to bite the bullet!

Call Breeze.

[D Stand]

If no luck with calling Breeze, I have one spare you can have. Even if it is just used to go source a few at local parts store before dropping the tank. I am just north of you in Bothell.

[lgordon]

Thank you to everyone who responded to my call for help! The problem was at the fuel level sender. Once I pulled the sender and the o-ring gasket out it was obvious that the paint around the o-ring had deteriorated and was bubbled and flaking off. I cleaned the mating surface on the tank well using a wire brush and CRC brake cleaner removing all traces of paint. I used one of the Ford rectangular cross section o-rings I already had and put a film of Permatex Permashield gasket sealant on top and bottom.

What made the job super easy was a getting a lock ring wrench from eBay. https://www.ebay.com/i/362841233602?chn=ps It took about one minute with a hammer and vice to reshape the wrench to give it more upward reach. Then, even though I have a dropped box in my trunk it was literally a three minute task to remove the sender access cover, lock ring, and pull the sender out. No dropping the tank and no hammering on it.

No more fuel smell!

129795129794

[stack]

That is a cool tool

stack

[RBachman]

Dittos on that. I've always used a couple screw drivers and they always seem to slip on me, LOL.
That is a cool tool

stack

[Peeker]

Did you end up doing the charcoal filter? I bought my kit partially assembled and the previous owner had one already installed.

[rich grsc]

So much for following the manufactures installation recommendations.

[silver_pilate]

So much for following the manufactures installation recommendations.

Yeah, the blurb about using a "fuel safe sealant" in the build manual really needs to be changed if it hasn't already. I did the same thing first time around and had a leak. Using a lubricant for installation is the way to go!

[lgordon]

129844My Coyote/TKO package came with what looks like an OEM canister and steel bracket so I installed it. I have no idea how it compares to the home made versions.

[phileas_fogg]

Yeah, the blurb about using a "fuel safe sealant" in the build manual really needs to be changed if it hasn't already. I did the same thing first time around and had a leak. Using a lubricant for installation is the way to go!

Yup. I used the "sealant" the first time too. And it leaked.


John

[JohnK]

Yup. I used the "sealant" the first time too. And it leaked.


John

Thanks for the heads-up about this everyone. I've assembled my tank but haven't put it in the car yet. I installed the square-profile o-rings with Permatex Permaseal, which is their "fuel resistant gasket dressing and flange sealant". Sounds like I should clean that stuff off and just dress the o-rings with oil before putting the tank in the car.

[lgordon]

The Permatex PermaShield worked well for me. Make sure you clean the depression where the o-ring seats! When I initially installed my tank I put oil on the o-ring but I didn’t remove the paint from where the seal sits. Bad! The paint deteriorated and was bubbling and flaking off resulting in lots of gasoline smell in my garage.

If you remove all of the paint from where the o-ring sits it’s probably ok to just use oil.

[Fman]

Yeah, the blurb about using a "fuel safe sealant" in the build manual really needs to be changed if it hasn't already. I did the same thing first time around and had a leak. Using a lubricant for installation is the way to go!

I just checked my build manual again, there was no mention that I can see about using any sealants or lubing o-rings in fuel level sending unit, vent or fuel pump. Did I miss something in the manual? My tank is not installed yet so now would be the time to go back and add some type of sealer. Any recommendation at this point?

[lgordon]

Where I saw the recommendation of using a sealant on the o-ring was in Factory Five’s video on installing the fuel tank. https://youtu.be/ybGdqmVyDV4

I compared the SealAll sealant the video showed with Parmatex’s PermaShield. For me SealAll set up way to quick and since it sets hard I was concerned about how difficult it might be to remove the sender later if needed. PermaShield is designed for parts that might need to be removed and reinstalled later.

[rich grsc]

I just checked my build manual again, there was no mention that I can see about using any sealants or lubing o-rings in fuel level sending unit, vent or fuel pump. Did I miss something in the manual? My tank is not installed yet so now would be the time to go back and add some type of sealer. Any recommendation at this point?
Well in post #18, I did say use engine, in post #28 I did reference manufacturers recommendations, engine oil. But why would Ford have a clue about how to assemble a fuel tank. So go ahead and glue it it place.

[Fman]

Where I saw the recommendation of using a sealant on the o-ring was in Factory Five’s video on installing the fuel tank. https://youtu.be/ybGdqmVyDV4

I compared the SealAll sealant the video showed with Parmatex’s PermaShield. For me SealAll set up way to quick and since it sets hard I was concerned about how difficult it might be to remove the sender later if needed. PermaShield is designed for parts that might need to be removed and reinstalled later.

I sent email to Dan at FFR regarding using a sealer, he got back to me today and mentioned if your having troubles seating the O ring to use a lubricant on it but a sealer was not necessary. Now I am really confused. I had a bad experience using a sealer on sending unit gasket with another vehicle, it ended up dripping into the fuel tank and caused all kinds of problems with clogging the fuel lines/filter.

I might just roll the dice and hope I have a good seal.

[silver_pilate]

Maybe that's where I saw it as well.

[Mark Reynolds]

It is a dry seal. There is no need to lube the square cross section o-ring. The o-ring DOES need to be located in its shallow groove in the tank. The sender or fuel pump sits on top of it so there is no sliding of the surfaces that touch the o-ring that could cause the o-ring to roll up. My guess is that in the original installation the o-ring was not completely in the groove.