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I have a strange problem with the fuel tank / evap in my 986S.
It varies in severity, but most of the time it will not take fuel in any significant amount without burping it back (backs up the neck).
Basically i have to add fuel for a few seconds, listen for it to begin to back up, let it subside, and continue. Dozens of times. Of at least a few.

Let's begin with some basics:

1.) the relay opens the filler seal - a) i *can* fill it and b) i hear the relay click
2.) there are no evap codes - in fact no codes at all
3.) I put a small hose down the filler neck with the fuel nozzle to vent it manually - no effect (maybe i submerged it?.... dunno)
and i should mention this vent hose also would have detected any physical blockage - it was basically a snake.....
i have not put a bore scope down...yet
4.) As one adds fuel, it gets less severe (e.g.: as it fills up it gets easier to get fuel in)
5.) sometimes -- and this seems to depend on temperature, it works normally or nearly so.
6.) it is NOT simply a matter of shutting off the nozzle. The fuel will, in a delayed reaction, come up the filler neck and spill out, as if under pressure.
6a.) ... even with a physical vent in place

I have not checked the entire venting apparatus since my wheel well liner has turned to stone... but I will, but if it was not venting i would expect an evap code.

has anyone heard of such an oddball situation? Any thoughts having to do with the strange shape of the tank?

TIA,

Grant

Grant gee-lenahan-at-vee-eff-email-dot-net
I believe it probably is a malfunctioning or partially obstructed vent valve - the one that opens when the fuel nozzle goes into the fuel filler.

After measuring the tank and the filler neck, i concluded that my physical vent that I snaked down ( a long way) probably was not long enough. That's a very long path that the fuel follows from cap to tank! I also concluded that the lack of a code/CEL means nothing, because a blocked or partially opening valve does not result in a venting of excess vapor to the atmosphere - which is all the EPA cares about. Car runs? Meh. And this thing is ooooold.

I wish i could determine better if it were good; but i don't have the diagnostic equipment to do so. I did pull it, and tried to blow through it. I could, but the flow was not huge. I don't have a reference to say if it is normal or not.

I did clean things as well as i could - the ground wire, the valve's exposed inlet and exit (with their little filter screens, buried deep). I did find that there is a manual work-around to a failed switch/sensor/solenoid - a little plastic tab on the side of the filler neck. I will try that. However, if the valve is internally restricted, it matters not if the solenoid or my screwdriver opens the valve - it will still have restricted flow. We shall see.

Could one of the lines be clogged? Sure. How to test? I dunno, without dis-assembling half the car. I have become very good at removing the fender liner though. M<ade tougher by plastic (the noun) that is 18 years old and not very, well, plastic (the adjective). I supposed i could put a manual vent from the tank lid to a manual valve - e.g.: a capped line or stopcock. Last ditch.

G

Grant gee-lenahan-at-vee-eff-email-dot-net
Also, the lines that go to the vent valve can get clogged.

I replaced the valve on my car at about 185k miles. It was really not that hard at all. But my wheel well liner is only made out of soapstone so it wasn't that bad.

This article was helpful:
[www.pelicanparts.com]

There are also several YouTube videos.

I first blew out the lines.
I actually had the valve out twice - once to clean it / test it (inconclusive) and once to put the stuuuupid magnetic sensor back in.

First time took a couple hours start to finish, 2nd time 30 minutes or so :-)

Which line(s) did you clean out? Where do i access it?

TIA,

Grant

ps: i do need to test and see if my cleaning fixed it. I've been away and the tank is full...

Grant gee-lenahan-at-vee-eff-email-dot-net
Purge valve line
Boxsterra - 3 weeks ago
#3 in this diagram.



There's another one that goes from the bottom of the valve all the way to another valve located under the driver's side manifold.

#3 in this diagram


... from the valve to the storage canister. And in your case that was a problem, eh?

Appreciate it

Grant gee-lenahan-at-vee-eff-email-dot-net
Yes
Boxsterra - 3 weeks ago
I think I have it right but my recollection is vague. The second line goes from one valve (in the wheel well) to another valve (under the intake manifold).

My symptom was totally different, no problem starting but just an annoying hooting sound on startup (not the starter bendix). I theorized that it might have been due to a clogged line causing a pressure buildup. It turned out to be a stuck valve (the one under the intake manifold).
So, as I think I told you,I removed the switch. I can't say I found anything wrong. However, I did blow through it, with low pressure compressed air both directions, and cleaned it with some electronics cleaner, and dried it as well as I could. I re-assembled everything, and today, went and tested it at the gas pump. It took 2 gallons no problem. This is six times more than it would typically take in one gulp.

Fixed? Does it make a difference that it was 46° out?

For the record, I had the same experience with my other (street )car — where dis-assemby, assembly and “no trouble found” was just what the doctor ordered. That was three years ago.

I guess I'll cross my fingers but this does not give me a warm and fuzzy feeling.

I like to find smoking guns.

I may clean that vent line "just because I can".

Thanks,

G

Grant gee-lenahan-at-vee-eff-email-dot-net
Unsatisfying
Boxsterra - 1 week ago
I know that feeling when you know there's a problem so you are happy to find it and unhappy for it to "fix itself". I suspect the valve is intermittently working, though blowing out the lines may very well have fixed the problem. Many have reported that.
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