Miata gas fumes part II - P0453, failure of gas tank pressure sensor? Pressure relief solenoid?

Ok, picking up from my last post on this; fuel filler and vapor hose replaced, and the car still gets nasty gas fumes, BUT, they only happen anymore on my trips to Mt. Lemmon.

At about 5500 feet or so, fumes come on like gang busters.

New to the process since changing out the filler neck hoses is that following the gas fumes, the car will now die within about two miles of the gas fumes hitting.

It is definitely fuel related.

First time it happened, car sputtered, but would run smooth at higher rpm (4500+, IIRC); turned the car around, back down the hill, runs fine everywhere else, no issues no gas fumes.

Second time was today, after cleaning the purge solenoid to see if maybe it was hanging up (and with 12v applied, functions fine). Same thing as first time, bad fumes above 5500ft, died, like died died, completely. Coasted backwards down the road to swing the car around, and once nose down, I thought I'd "bump start" it - which actually worked, car fired, so tempting fate I turned back around to go to the top of the mountain. Car ran fine all the way up, all the way down, no issues, no gas fumes.

Prior to the run up, the boy puts his OBDII reader on it, code P0453, which is the vapor/purge system (however they call it). Never had a CEL or anything. Upon putting the car back together, no more code. "self cleared"?

Today, at the bottom of the mountain, I did get a CEL, but not sure where the boy's OBDII tool is,so not sure if it's the same code or I have a new one.

Anybody else experience this? Is it likely one of those two sensors? The little purge tank up front getting gassed, putting too much fuel in the canister at the rear?

Madness.

Bump. None of y'all have ever had fumes issue NOT related to filler hoses?

How much gas in the tank? Full? half-full? Near empty?

Amount in tank matters not at all. Next step is to re-route the vent hoses at the bottom so that the tank is "always vented" and run the car back up the hill.

If it doesn't vaporize then, it tells me either bad sensor or bad solenoid (or so I think).

The other part of this is that some have said aftermarket exhaust may be heating the gas tank causing the pressure build, but my thought is I'd smell it all the time if that were the case, and it only happens anymore on my runs up the mountain, and always at the same point on the drive.

We'll see.

The "pressure build" is compounded by a "pressure fall" on the outside of the tank. The change in atmospheric pressure is enough to crush an empty soda bottle last opened at Mt Lemmon's 9,000 foot altitude. Frankly, the bottle will crush itself even if exposed to 6,000 - 7,000 feet.

I was hoping Keith would chime in, since they're in CO, and maybe he's heard of it, it's common, etc... but I should think if the tank is able to vent, pressure changes equalize at venting, right?

That solenoid opening isn't very large (appears to open about half the diameter of the tube), but would think to vent it wouldn't need much anyway.

Just curious...As a stopgap, did you try opening the fuel cap to equalize the pressure? It's not a cure but changes could put someone on to the solution.

I have done that, and I don't notice pressure out of the gas cap. The aroma is definitely strongest on the side of the car with the vent hoses (i.e. passenger side).

As I think about that, maybe it's excess gas in the return line hitting the canister. As I read, there's a "percolation" canister up the front half of the car, which all I've read on Miata.net says is not charcoal filled (that's the rear of the car).

That lends credence to the "aftermarket" exhaust heating the gas tank, which fuel would heat up "quicker" at higher altitudes. That said, why, upon getting the car to refire and driving it the remainder of the way up the mountain and all the way down do I not experience the fumes?

Perhaps stopping the car for a few minutes allows things to cool sufficiently? Excess gas in the canister evaporates?

Or either canister is cracked. Certain cars are known for it. Not sure if your Miata is one of them.

Update: During my search on Miata.net someone had mentioned aftermarket exhaust seeming to be the culprit of his fuel aroma therapy - too much heat on the gas tank causing vapor expansion; on mine, I've done some fitting and welding of cheapo hot rod shop tubing after the resonator, and it is not going to hold heat like the factory stainless. Man was that gas tank warm!

So I got some of the El-cheapo autoparts store "titanium" exhaust wrap, applied liberally to the exhaust.

I drove up Mt. Lemmon yesterday, and behold, NO gas fumes! It was cooler than usual, but not significantly so (maybe 10 degrees from my last trip?), but it'll be warm this weekend so I'll go again.

Bottom line, I think the cheap thin exhaust tubing I used behind the resonator was throwing off a lot of heat and cooking the gas tank too much, exacerbated by altitude.

Yeah the temp was different but Mt Lemmon was just as tall. I think we're done here.

In reply to OldGray320i:

That's good to know. I haven't had fumes in my NB since I replaced the fuel filler hose, but I did ditch the heat shield when replaced the muffler. Maybe that was a mistake. Good thing it's still in the barn.

In reply to Woody:

Not sure muffler area was complicit (though I wrapped the tubing there too...), it was the tubing coming out of center resonator which is directly underneath the gas tank.

Also keep in mind that after I finally swapped the filler hose, this only happened at a change in altitude, and at about a mile or so up.

You're probably fine (famous last words - keep that sheild!).