GBalthropXJS@aol.com wrote:
I have tested the much-maligned Rochester valve located at the
charcoal canister in front of the left-front wheel well, and it opens
when the slightest vacuum is applied to the vacuum port, releases
pressure (no vacuum applied to vac port) when 1.5 p.s.i. is applied,
and vents vacuum when the slightest vacuum is applied to the tank side
(~ 1 In.Hg.). This testing done with a Mityvac Silverline Plus 4050.
So I’m now looking for other possible explanations for excessive tank
pressure, and all I’ve found so far is the fact that in the recall,
the tech left the 2 p.s.i. valve between the vapor pipe and the vapor
separator in the boot (valve located next to separator on right side
of fuel tank).
That’ll probably do it. Since the 2 psi vent valve and the Rochester
valve are thereby connected in series, the pressure will have to rise
to the total before any venting occurs. When the engine is off,
you’d have to build pressure to 1.5 + 2 = 3.5 psi for it to vent, or
vacuum to 1 + 2 = 3 psi. When running, even with the Rochester valve
full open as it should be, you’ll still need to exceed the 2 psi
required by the vent valve to get any venting. That will cause a
whoosh, and the apparent size of the whoosh depends on how full or
empty the tank is; on a full tank it’ll be an itty bitty whoosh, but
with a nearly empty tank it’ll be a big whoosh.
The specific question I have is: How does the Vapor Separator
function?
It’s an empty metal can with several tubes going into the bottom.
One of these tubes actually extends up inside the can to near the
top; this is the one that connects to the line to the carbon
canister. The vents from the top of the fuel tank connect to the
others. When something comes up the line from one of those vents, it
may be air, it may be fuel vapor, it may be a mist of vapor and
liquid droplets, or it may even be liquid. In the can, all the
liquid will obviously settle to the bottom of the can and drain down
one of the vent lines back to the tank. Only gaseous components –
air or vapor – will escape through the tube opening near the top of
the can.
Also, are there any known failure modes of the separator (other than
external leakage of fuel which is NOT occurring in my case), or any
tests for operation/obstruction of the separator?
As far as I know, the only known problem is the generation of rust
particles. This thing is as likely to put rust particles in the fuel
system as anything else. While I was lining my fuel tank, I lined
this vapor separator too. Not easy to do, you’ve gotta pour stuff in
through one of the tiny tubes, shake it all around, pour it back out.
Finally, is there a specific attachment relationship between the tank
tube fittings and the separator tube fittings which is known?
Yes. The line to the carbon canister MUST be connected to the tube
that extends to near the top of the separator. If you don’t know
which one that is, take a piece of wire and turn a tiny hook on the
end and insert it into each tube and see how far in it hooks on the
end of the tube. All but one will end right at the bottom of the
vapor separator. The one will extend several inches inside. Mark
that one somehow so you won’t forget.
Both
mine (85 and 89) have the fittings as follows: Vapor pipe from
canister goes to Forward fitting on separator; Upper Left fitting on
tank goes to Rear fitting on separator; Upper Right fitting on tank
goes to Right fitting on separator; Bottom fitting on tank goes to L
fitting on separator; All locations are as viewed from vehicle rear &
forward is toward front of vehicle.
Perhaps it should be pointed out that the vapor separator on the
convertible is apparently a completely different animal. On the
coupe, the can is upright within the right side flying buttress. On
my '83, it actually had a wedge in the mount, as though they were
REALLY picky about the angle at which it was mounted, although I
can’t fathom why, pretty much anything close to this-end-up should do
it. On the convertible, the vapor separator is supposedly a long
skinny can designed to lay horizontally above the tank near dead
center of the car. The function remains the same, though; within
this little can, the opening to the carbon canister is at the top
center and all the openings to the tank are at the bottom.
Without knowing the internal configuration of either the tank
fittings, or the separator fittings, it is impossible to understand
the system, so if anyone has any info on either, it would be much
appreciated.
The vent fittings from the tank are actually pretty easy. There’s
supposed to be a vent connection from the high point in any corner.
IIRC, there’s one at the top left corner of the tank, one from the
top right corner, and one from the filler neck.
Now, there’s a recall that added a vent from the surge tank. In the
original configuration, the surge tank was vented into the main tank,
and only about halfway up the main tank. Hence, if the main tank was
more than half full, the vent was immersed. Can this hurt anything?
I don’t see how – but since there was a recall, I presumed it must
somehow. Perhaps it caused suction problems for the fuel pump, like
maybe it needed a clearer vent to deal with the suction flow pulses.
The recall involved replacing the pickup tube with a new one, the
only difference being that the new one had a barb for a vent
connection mounted in the disc. The original vent was left alone,
just another vent was added. A hose from this new barb was routed up
to the vapor separator and teed into a vent line up there.
I didn’t actually purchase the new pickup tube. You could just
modify an existing one, but I didn’t do that either. Instead, what I
did was tee into the existing vent line from the surge tank to the
main tank and run a vent line from there all the way up to teed into
one of the vent hoses into the vapor separator. Everything always
worked fine for me that way, although I can’t say I ever noticed a
problem BEFORE I did that.
– Kirbert
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