Gas Fumes on F53 Chassis Rig

[TriMoot]

So here goes..hoping someone else has experienced this:

We have a 1997 Rexhall RexAir, 32' on a Ford F53 chassis with a 75 gallon gas tank and 38K miles.

We have heavy gas fumes in these two situations:

1. When putting gas in: If I fill it quickly, using the full volume ability of the hose, the fumes inside are intense and 1st appear in the bedroom and bathroom which are both in the back. If I fill it slowly we still get fumes but not as bad.

2. When pulling large and long hills (White Bird hill and the one coming out of Lewiston, ID) before we get to the top the fumes are very strong.

In both instances the O2 sensor or whatever it's called goes off and of course we no longer can keep our fridge cool until we get the fumes cleared out.

Just last night I took a strong light and crawled up and down the length of the motor home underneath hoping to find an obvious issue, perhaps a broken vent hose or any signs of leaks, unfortunately I didn't find any.

If anyone has experienced this or has any suggestions let me know.

Not that this matters, but the gas gauge doesn't work, never has since we've owned it which was just last November.

Also, I've replaced the fill hose as it was leaking. That was about 4 months ago.

Thanks in advance for any and all input.
Tri

[subford]

I was going to say the fill hose but you replaced that.
So I will say check the generator hose.
If that is OK check the the vapor lines going from the tanks rollover valve to the charcoal canisters.

[TriMoot]

Bill, thanks for the quick response. Hmm, ..."vapor lines ...rollover valve..charcoal canisters"..hmm, think I'm going to have to do a bit of research to find out what those are.

I did follow a line last night, on the line was printed, "Fuel Ventilation" and it lead to the generator which surprised me. So that wasn't the ventilation hose I was looking for.

There's so many of them. I think what I'll need to do is cut all the zip ties and let things come loose and then try and follow them again.

I did find a post this morning:
Here: RV.Net Open Roads Forum: Class A Motorhomes: Strong gasoline smell at tank ???

And Here: RV.Net Open Roads Forum: Class A Motorhomes: Follow-up on dropping gas tank

Talks very similar to what i'm experiencing and about lowering the gas tank..gulp.

Thing is, I kind of want to do that as I REALLY would like to get the gas gauge working, but I have somewhat bad arthritis in my thumbs, so thinking about all that work makes them ache even now!

Again, thanks for the input.
Tri

[TeJay]

Tri,
The fuel storage/fill systems as a result of emissions are somewhat complicated. The fumes are first separated by a fuel vapor separator then trapped into a vapor canister which is purged at a later time by drawing fresh air through the canister. The charcoal canister stores the vapors until they are purged.

These systems require very little maintenance and that's why most techs know very little about them. About the only service that is routinely performed is to replace a thin gauze filter on the bottom of the charcoal canister about every 30,000 miles and that may have changed.

Since your fuel gauge is not working your best bet would be to drop the tank, inspect all hoses looking for blockages, kinks, leaks, etc. Something is wrong not allowing things to work as designed. A good exam may be the only way to determine the exact issue.

TeJay

[subford]

Fuel Tank Venting
Fuel vapors trapped in the sealed fuel tank are vented through the orificed vapor valve assembly in the top of the tank (I called it a roll-over valve). The vapors leave the valve assembly through a single vapor line and continue to the carbon canister (located in the engine compartment or along the frame rail) for storage until they are purged to the engine for burning.

Canister Purging
Purging the carbon canister removes the fuel vapor stored in the carbon canister. With a purge port system, the vapors flow from the carbon canister to the throttle body. With an EEC controlled EVAP system, the flow of vapors from the canister to the engine is controlled by a EVAP Canister Purge solenoid valve. Purging occurs when the engine is at operating temperature and off idle.

[TeJay]

subford said it right. That's the complete system in a few good sentences. You are still charged with trying to figure out exactly what is not working. You may be able to access some of it without taking the tank out or not. The real issue is what or how are you going to diagnose what is not working??

The computer will purge the canister when it decides to do so. The fumes just leave the sealed tank and are stored in the canister. Visually inspecting the stuff is where I'd start because you can't run tests on anything. Well I don't know for sure about that last sentence but as long as I've worked on vehicles I've never read about or heard of anybody running tests on the system. Why? Because there is so little that goes wrong with it.

Here's a thought!! If vapors are leaving the tank maybe the gas cap is bad and not sealing the system. Inspect the gas cap. If it looks suspect just replace it.

TeJay

[TriMoot]

You know TeJay, THAT is a VERY good idea..duh! Don't know why I didn't do that right off the bat! I'm going to run out today (tomorrow) and buy one ASAP. I WILL report back if that's all is was. And then I'll let everyone take turns kicking me in the rear!

Thanks again folks!
Tri

[Brockx]

I read somewhere on this forum that the hose connection assembly on the top of the tank can become dislodged. If I really cram the tank on a fill-up (nose down attitude at the pump) I will get a little odor outside near the entry door.

[Lincolnut]

In your first post you said the fumes are real bad "while you are PUTTING Gas" in the coach and you have to do that with the gas cap off so how can the gas cap be part of the problem?

I think you must have a fill/vent line that is still not right on top of the tank that you may not be able to see until the tank is removed....my .02 and it may not even be worth that....

Mike

[TeJay]

Lincolnut,
You have a good point about the fumes while filling the tank. Sometimes I don't go back and read what an OP says. But it was just a thought. We also can't rule out certain items just because it does not appear to be connected. I've done that in the past and has come back to bite me. The worst is when a persons says, "Well I changed this or that so they can't be the problem." Three hours later we find a defective part was installed. Changing the cap is not an expensive deal. The gas cap just like the radiator cap has more than one function. The cap prevents venting of fumes but also allows air to enter as the fuel is burned. It's a sealed system with few parts to go wrong. Also with the age of his coach it's probably prudent.

It will be interesting to finally learn the fix.

TeJay

[Lincolnut]

TeJay,

You may be right and that gas cap does not cost much and could be a small part of the problem but I think he will find a vapor leak on top of the tank 'when' he has to drop the tank.........sorry but I think he will have to drop the tank......

Mike

[TeJay]

Lincolnut,

Yep I hate to agree (for the OP's sake) and that was my thought in post #4. To do this right (unless he's real lucky) the tank will have to come out. While he's there he can fix/change the fuel pump and get the gauge to work or at least eliminate anything in the tank as the possible cause.

TeJay

[mrv8outboard]

Just put it on a smoke machine and be done with it.

[chboone]

Below is a link to a discussion about dropping the fuel tank. There is a picture with the tank already dropped.

http://www.irv2.com/forums/f105/gas-...-210783-2.html

Chuck