I don’t think OBD1 will flag a bad carbon cannister or will
it?
Is there easy test to check if it is full of liquid or
working correctly?–
John 90 XJ40
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Hi John,
On your 1990 model, there is a purge control valve in the plumbing near
the intake manifold, in the hose line between the canister (located
forward of LF wheel) and a port in the intake manifold. That purge
control valve is operated by the ECU and is supposed to open when CTS
temperature reaches 43C, drawing/purging fuel vapor from the charcoal
in the canister.
The evaporative loss system (lines to the canister) NEVER have any fuel
in liquid state in them. There is simply a VAPOR line from the top of
the gas tank to the charcoal canister, where vapor from the space above
the liquid fuel level in the tank passes to the canister when the fuel
warms, and vapor pressure above the fuel increases.
I would suggest testing with a MityVac pressure/vacuum pump and gauge,
or equivalent, to make sure the vapor line between the tank and
canister is not damaged or blocked. If you apply pressure to the line
at the tank end, the pressure should NOT exceed 2 PSIG before a valve
opens to bleed that pressure. The same should apply when you put
vacuum on the tank end of the vapor line. Likewiise the purge control
valve should be open (NOT allowing any pressure to be developed when
putting pressure on the canister side of the valve, with the engine
running and coolant temperature > 43C (warm engine).
I’m not familiar with any fault code related to purge valve operation,
but then I don’t have a 4L.
If the purge system is working correctly, you will have NO “whoosh” or
release of either pressure or vacuum when opening the fuel filler cap
while the motor is warm and running, or immediately after shutdown.
You should have a moderate whoosh, relieving up to 2 PSIG vapor
pressure from the tank, when you open the filler cap after the vehicle
has been sitting in the sun on a warm day. A large whoosh that lasts
more than ~ 1 second, or “oil canning” or deflection of the sheet metal
of the tank upon opening the filler cap indicates the system is NOT
properly venting.
What symptoms are you having that make you feel you have a vapor
recovery system problem?
George Balthrop, Clifton, VA USA
85 & 89 XJ-S Coupes; 89 XJ40 VDP-----Original Message-----
From: John S js4453@att.net
I don’t think OBD1 will flag a bad carbon cannister or will
it?
Is there easy test to check if it is full of liquid or
working correctly?
–
John 90 XJ40
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In reply to a message from gbalthropxjs@aol.com sent Wed 16 Apr 2008:
Describing the amount of whoosh is difficult. I think
after sitting the whoosh does last for more than a second
although I am not sure of the length of time. Sometimes if
I very loosely hold the cap while unscrewing it, the cap
will raise up after unscrewed. Now it isn’t flying off
into the air but it definitely lifts up. Is that 2 psig? I
don’t know.
Lately I have smelled gas fumes inside the cabin. Not
everyday, not all the time but sometimes.
Getting to that valve takes a bit of gymnastics. Not much
room for the arms up there. I get to it my loosening the
inner wheel well cover to the point it can move a bit,
remove the big round air duct - the one that allows air to
pass through the spoiler. Then I have access to the carbon
cannister.
Should I be able to hear that valve click when you turn the
key to the one position? Those valves are about
$130…ouch. In my old SIII it was mechanical not electric
and cost a few dollars.
Are we talking about the same valve? The one I am thinking
of is right at the carbon cannister and is electrically
controlled.
Is it at all possible without tearing the car apart to see
where it attaches to a port on the manifold?–
The original message included these comments:
the intake manifold, in the hose line between the canister (located
forward of LF wheel) and a port in the intake manifold. That purge
–
John 90 XJ40
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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Hi John,
Perhaps someone with a 1990 4L can tell you exactly where the purge
control valve is, as I have an 89 that has a different valve that is
vacuum controlled rather than electrically controlled by the ECU. If
you are looking at a valve that has a vacuum line on its top, or no
electrical wiring, that is NOT the electrically-operated Purge Control
Valve I am referring to. My understanding is that the Purge Control
Valve is somewhere under the intake manifold. If you remove the air
cleaner and then trace the rubber hose coming from the canister
rearward toward the manifold, you should be able to find that valve,
and the manifold port upstream of the valve. It’s crowded under there,
so you might even have to remove the MAF and the hose up to the
throttle body to get a clear look at the purge lines and valve.
Probably the easiest way to test the system is to run the engine until
warm, put a pressure pump/gauge on the vapor line that runs from the
top/rear of the tank forward to the canister, and see that it releases
pressure when 2 PSIG pressure is attained, rather than allowing
pressure to exceed 2 PSIG. Then start the warm engine, and make sure
that there is no pressure allowed to build at the same vapor hose.
You didn’t say: Do you ever get a whoosh from opening the filler cap
with a warm engine running, or immediately after warm engine shutdown.
If you get NO whoosh under those circumstances, then the purge control
valve is operating properly.
Yes, if you had never noted the amount of “whoosh” that you get from a
properly operating system, it IS difficult to tell how much whoosh is
too much 
Basically anything lasting less than 2 seconds, with NO tank sheet
metal deflection or “oil canning” is probably OK. Please do that
whoosh test with a warm engine running and let is know what you find.
Another possible failure mode of the canister system is for the vapor
line to get plugged, and you draw a vacuum on the tank as a fuel is
used from a full tank, which can result in preventing proper fuel pump
pressure and or collapsing of the tank. This would result in a very
violent whoosh when opening the filler cap after driving for an hour or
two after a fill-up.
A more critical cause of fuel vapor in the cabin could be a leaking
Fuel Injection hose or fitting on the left side of the engine,
particularly if your “Duckbill” is missing or damaged. Such fumes can
also be drawn into the air intake plenum at the base of the windshield.
I would carefully inspect for any such leaks around the engine, and
check for fuel odor under the bonnet.
George Balthrop, Clifton, VA USA
85 & 89 XJ-S Coupes; 89 XJ40 VDP-----Original Message-----
From: John S js4453@att.net
Describing the amount of whoosh is difficult. I think
after sitting the whoosh does last for more than a second
although I am not sure of the length of time. Sometimes if
I very loosely hold the cap while unscrewing it, the cap
will raise up after unscrewed. Now it isn’t flying off
into the air but it definitely lifts up. Is that 2 psig? I
don’t know.
Lately I have smelled gas fumes inside the cabin. Not
everyday, not all the time but sometimes.
Getting to that valve takes a bit of gymnastics. Not much
room for the arms up there. I get to it my loosening the
inner wheel well cover to the point it can move a bit,
remove the big round air duct - the one that allows air to
pass through the spoiler. Then I have access to the carbon
cannister.
Should I be able to hear that valve click when you turn the
key to the one position? Those valves are about
$130…ouch. In my old SIII it was mechanical not electric
and cost a few dollars.
Are we talking about the same valve? The one I am thinking
of is right at the carbon cannister and is electrically
controlled.
Is it at all possible without tearing the car apart to see
where it attaches to a port on the manifold?
–
The original message included these comments:
the intake manifold, in the hose line between the canister (located
forward of LF wheel) and a port in the intake manifold. That purge
Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting
services
and resources including Photo Albums, Event Diary / Calendar, On Line
Books and
more !
Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !