When ambient temps rise above 95f the engine acts as though
starved for fuel after running about 3 hours. After sitting
just 20 minutes it will restart and run without further
incident. If the air temperature is below about 95 degrees
it does happen at all.–
clarkecars
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In reply to a message from clarkecars sent Sun 28 Jun 2009:
Try loosening the fuel filler cap and run that way. Your problem
should vanish. There are a couple of little thermal valves on the
thermostat housing with plastic lines to them. When the engine
comes to temperature (meaning it’s running) the valves open,
putting intake manifold vacuum on the charcoal canister to purge it
of accumulated vapors. The canister is tubed to the vapor space of
the fuel tank, and two small rubber hoses allow air into the tank
to establish a flow through the canister. You’ll see the hoses
poking through the front wall of the trunk under the car just
behind the differential.
Those hoses will clog with dust and varnish (or a mud dauber wasp)
and put the fuel tank under a vacuum. If the vacuum is too strong,
the tank will collapse in on itself. But usually the vacuum is
just enough to cause the gasoline to flash to vapor right at the
suction of the roller-type fuel pump. Loosening the cap allows
another source of air into the tank to prevent that flashing from
occuring.
The permanent solution is to poke a wire into the hoses to clear
the obstructions. You don’t want a loose filler cap during a heavy
rain.–
The original message included these comments:
When ambient temps rise above 95f the engine acts as though
starved for fuel after running about 3 hours. After sitting
just 20 minutes it will restart and run without further
incident. If the air temperature is below about 95 degrees
it does happen at all.
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In reply to a message from clarkecars sent Sun 28 Jun 2009:
On the early cars with an external fuel pump, there is a
known problem of fuel line cavitation when the pumps are
worn whilst driving in high ambient temperatures. The hot
fuel returning from the fuel rail is directed straight to
the fuel pump pick-up in the tank and eventually this causes
the problem particularly at low fuel levels. The problem can
often be overcome if you keep the fuel tank fairly full -
certainly above one-quarter full and can often be overcome
by simply adding fresh (cold) fuel.
Jaguar Cars North America produced a modification which
involved the installation of a second fuel pump, but, since
to fit that you need to buy another fuel pump, it makes more
sense to simply install a new fuel pump to replace the worn,
tired old one.–
The original message included these comments:
When ambient temps rise above 95f the engine acts as though
starved for fuel after running about 3 hours. After sitting
just 20 minutes it will restart and run without further
incident. If the air temperature is below about 95 degrees
it does happen at all.
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In reply to a message from clarkecars sent Sun 28 Jun 2009:
Ealy XJ40s (those with fuel pump outside the fuel tank) are
certainly prone to vapor locks - even the owner’s manual suggests
that. I have recently experienced this with my '89 XJ40, on which I
have replaced fuel pump (the pump completely died) 6 months
earlier. Driving on a 95 F aftrnoon, 30 miles 30 mph continuous
uphil winding road towards a hiking trail, half-tank, the engine
just died. It would restart, run for few seconds (transmission in
park) and die out. I rolled the car downhill to a safe spot and
enjoyed the nature for some 30 minutes. The car started fine nd we
drov off as if nothing happened. 2 months later and with fall in
full swing, this has not happened again since.–
'89 XJ6 '90 Daimler
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In reply to a message from Zigmund sent Fri 6 Nov 2009:
Try loosening the filler cap when it happens again. There are two
small rubber hoses which allow air into the tank as the evaporative
emissions charcoal is being purged of accumulated vapors. The
hoses can plug up and create a good vacuum in the tank and the fuel
vaporizes in the pump suction hose. Loosening the cap will provide
another point for air ingress.–
The original message included these comments:
Ealy XJ40s (those with fuel pump outside the fuel tank) are
certainly prone to vapor locks - even the owner’s manual suggests
that. I have recently experienced this with my '89 XJ40, on which I
have replaced fuel pump (the pump completely died) 6 months
earlier. Driving on a 95 F aftrnoon, 30 miles 30 mph continuous
uphil winding road towards a hiking trail, half-tank, the engine
just died. It would restart, run for few seconds (transmission in
park) and die out. I rolled the car downhill to a safe spot and
enjoyed the nature for some 30 minutes. The car started fine nd we
drov off as if nothing happened. 2 months later and with fall in
full swing, this has not happened again since.
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In reply to a message from Zigmund sent Fri 6 Nov 2009:
I had the same exact experience in the everglades last
spring. Filled tank completely in Lauderdale and car started
dying on the top of the Sunshine Skyway Bridge and
subsequently every 10 min after that. Stopped, cooled down
and it restarted immediately. Limped it to Clearwater and
opened gas cap and it let out a big burp- that’s vapor lock !–
DashXJ6
Buffalo, New York, United States
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In reply to a message from DashXJ6 sent Sat 14 Nov 2009:
hi guys.
as a non-mechanic, just wondering if someone could elaborate on
this vapour lock thingy.
i always keep my fuel tank full and fill up once it gets to around,
3/4 full mark.
when I get to the petrol/gas station and un-screw the cap, I always
get that wush of air release from the tank.
is this supposed to happen then or not?
as DASHXJ6 states above, his dies out every 10 mins but allowing to
cool down and un-doing the cap makes it fine. yet i m getting this
vapour lock , yet my car is running a dream!!
assuming i m missing something here.–
The original message included these comments:
and it restarted immediately. Limped it to Clearwater and
opened gas cap and it let out a big burp- that’s vapor lock !
DashXJ6
Buffalo, New York, United States
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Technically what he refers to is not what I would call vapour lock.
Vapour lock is when the fuel boils and turns to a vapour. Pumps can’t pump
the vapour and the car stalls.
In the situation he refers to is a failure of the tank ventilation system.
As you remove fuel from the tank air has to enter to replace the fuel in the
tank otherwise a vacuum is created in the tank and eventually the pump can’t
pump against it. In some rare cases the tank can actually buckle.
The reverse is also true in that after you fill up the tank and park in the
sun the hot sun will cause the fuel to expand. In the old days this excess
pressure was ventilated to the atmosphere. Now it is captured in a charcoal
canister and drawn back into the engine when its next run.
I think if everything is working well the tank will stay within a +/- 3lbs
pressure or so. So depending on the situation you can get a bit of a
pressure(- or +ve) in the tank even if everything is okay.----- Original Message -----
From: “XJ40-MARK” xj40mark@hotmail.co.uk
To: xj40@jag-lovers.org
Sent: Saturday, November 14, 2009 1:06 PM
Subject: Re: [xj40] vapor lock?
In reply to a message from DashXJ6 sent Sat 14 Nov 2009:
hi guys.
as a non-mechanic, just wondering if someone could elaborate on
this vapour lock thingy.
i always keep my fuel tank full and fill up once it gets to around,
3/4 full mark.
when I get to the petrol/gas station and un-screw the cap, I always
get that wush of air release from the tank.
is this supposed to happen then or not?
as DASHXJ6 states above, his dies out every 10 mins but allowing to
cool down and un-doing the cap makes it fine. yet i m getting this
vapour lock , yet my car is running a dream!!
assuming i m missing something here.
The original message included these comments:
and it restarted immediately. Limped it to Clearwater and
opened gas cap and it let out a big burp- that’s vapor lock !
DashXJ6
Buffalo, New York, United States
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services and resources including Photo Albums, Event Diary / Calendar, On
Line Books and more !
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If removing the fuel filler cap with the engine running and warm
results in a “whoosh” of air either escaping from, or entering into the
tank, that is NOT “vapor lock” but rather an indication that the
Evaporative Emission Control system is NOT working properly.
There is a 2 PSI valve in the vapor line that runs from the vapor
separator at the top of the fuel tank to the charcoal canister at the
front, and there is a purge valve that is open, relieving any pressure
from the canister, when the engine is running and warm.
The purpose of this system is to minimize the amount of fuel vapor
which escapes into the atmosphere when the car sits with the engine
off, outdoors in the sun, and the vapor pressure above the fuel in the
tank increases with temperature of the fuel. The charcoal in the
canister absorbs fuel from the vapor from the tank and releases
pressure to the atmosphere when the tank vapor pressure reaches about 2
PSI.
If that valve is NOT releasing pressure (either positive or
negative/vacuum), if you start with a full tank and very little air
above it, after using a signifcant amount of fuel, you now have a
partial vacuum above the fuel (no more air has been allowed to enter
then tank as the cap seals completely and the vapor line is NOT
allowing air to flow from the canister into the tank), and this can
stall the fuel pump. In this scenario, opening the filler cap allows
air to enter the tank, with a big whoosh, likely accompanied by
“oil-canning” or deflection of sheet metal in the fuel tank (can damage
the tank), and the fuel pump can now function again.
George Balthrop, Clifton, VA USA
89 and 85 XJ-S Coupes; 89 XJ40 VDP-----Original Message-----
From: XJ40-MARK xj40mark@hotmail.co.uk
just wondering if someone could elaborate on
this vapour lock thingy.
i always keep my fuel tank full and fill up once it gets to around,
3/4 full mark.
when I get to the petrol/gas station and un-screw the cap, I always
get that wush of air release from the tank.
is this supposed to happen then or not?
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In reply to a message from XJ40-MARK sent Sat 14 Nov 2009:
Mark,
The symptom described by DashXJ6 - i.e. a rush of air out of
the tank when the filler cap is removed after a long, hot
journey - is NOT vapour lock which would cause engine
running problems…
This is a simple description of vapour lock :-
A rush of air out of the tank when you open the filler cap
is caused by a build up of vapour pressure created within
the tank. The pre-'91 cars with the external pump and their
design of the tank venting system are particularly prone to
that phenomenon. The tank venting system was re-designed
when they introduced the in-tank pumps in 1991 to minimise
the fuel blow-back when removing the filler cap, but even
with that ‘improved’ vent system, Jaguar noted that:-
‘‘If the vehicle has been standing for a while there may be
some pressure released when removing the cap - dependent
upon ambient temperature’’.
The introduction of the immersed in-tank pump was designed
to assist fuel pump cooling to overcome the problem of
over-heating experienced by owners with cars using the
external pump in high ambient temperatures.
As you can read from the link above, true ‘vapour lock’
occurs when the fuel in the fuel rail / feed lines vaporises
due to excessive heat. Consequently, the fuel pump cannot
work properly - causing ‘cavitation’ - and hence the engine
runs poorly or even cuts out completely. When the fuel lines
/ pump cool down a little and the fuel returns to its liquid
state so that the pump can operate, the engine can be
restarted and it runs perfectly normally.
It often helps if new, cold, fuel is added to the tank to
speed up that process.
Obviously, since the fuel lines exit the bottom of the tank
and are therefore always covered in liquid fuel, the fact
that the fuel vapour above the fuel is pressurised and
causes the ‘burp’ when the filler cap is removed it has no
direct bearing on the ability of the fuel pump to pump
liquid fuel. It is the conversion of liquid fuel to vapour
in the fuel rail / feed lines and pump due to excessive
temperature in the fuel itself which causes the engine to stall.
This latter phenomenon can also result in ‘hot start’
difficulties if the fuel pressure in the fuel rail drops
rapidly after engine shut-down - i.e it does not maintain
the required ‘hold pressure’ due to a faulty fuel pressure
regulator or fuel pump check valve. The sudden drop in
pressure causes the liquid fuel in the hot fuel rail to
‘boil’ and vaporise, thus causing a genuine ‘vapour lock’.
I had that very problem on my '91 car and a new fuel
pressure regulator immediately solved the problem.–
The original message included these comments:
as a non-mechanic, just wondering if someone could elaborate on
this vapour lock thingy.
when I get to the petrol/gas station and un-screw the cap, I always
get that wush of air release from the tank.
is this supposed to happen then or not?
as DASHXJ6 states above, his dies out every 10 mins but allowing to
cool down and un-doing the cap makes it fine. yet I m getting this
vapour lock , yet my car is running a dream!!
assuming I m missing something here.
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In reply to a message from Bryan N sent Sat 14 Nov 2009:
great explanation brian, understood with thanks!
when I stated earlier that I get the whoosh out the tank when I
release the filler cap, I would say it is nt really a whoosh , but
more like opening a bottle of fizzy pop sound.
i was reading up on this in the haynes manual earlier and it
describes in there that a dual fuel pump can be fitted to remedy
this problem.
is this something worth doing or is it a case of a problem not
causing a problem, so leave it?–
The original message included these comments:
The symptom described by DashXJ6 - i.e. a rush of air out of
the tank when the filler cap is removed after a long, hot
journey - is NOT vapour lock which would cause engine
running problems…
Bryan N, '91 Sovereign 4.0 L, RHD
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In reply to a message from XJ40-MARK sent Sat 14 Nov 2009:
Mark,
You may have read about a modification to install twin fuel
pumps to prevent ‘‘fuel pump noise (chattering) and/or engine
stalling in hot weather caused by fuel vaporisation at the
fuel inlet to the pump’’.
There was a TSB 19-22 published in June 1993 by Jaguar NA
applicable to all XJ40s with external pumps so affected to
fit a second pump in series with the first (parallel wired)
to obviate this problem. The job required quite a bit of
re-plumbing.
However, since the problem only seemed to affect pumps which
had many miles on them and were therefore well worn and you
need to buy a second pump anyway, the simpler answer would
seem to be just to replace the original pump with a new one
and drive for another few years with no problem.
I very much doubt that your car will suffer from that
problem in the UK - it just will not get hot enough, despite
what the Temperature Taleban keep telling us!–
The original message included these comments:
I was reading up on this in the haynes manual earlier and it
describes in there that a dual fuel pump can be fitted to remedy
this problem.
is this something worth doing or is it a case of a problem not
causing a problem, so leave it?
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In reply to a message from George Balthrop sent Sat 14 Nov 2009:
It was a first time thing not like our DB5’s that can vapor
lock every other drive. Circumstances were: close to 98
degrees and my pals guy overfilled tank to give me my
money’s worth. Lived in Florida 20 plus years and this was
the first vapor lock in this Jag.–
DashXJ6
Buffalo, New York, United States
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An old post i know - but my 1988 55k 3.6 vdp does this. I changed the original pump for a new Bosch pump and its just the same. Quiet as a mouse when cool and above 80 external or when the car has stood in traffic the cavitation starts. So its not a pump issue for sure.
Did anyone try the twin pump solution? I already wrapped my exhaust pipe above the new pump and can confirm this is not the cause - the pump is cool when the cavitation happens. Im going to wrap the fuel lines best i can under the bonnet/hood as a first step
My 1990 4.0 XJ40 suffered with this problem a number of times. A new pump was not the solution so I had a fuel cooler installed under the car on the return line to the tank. I also fitted insulation wrap on all the accessible exhaust system components especially the ones near the pump. Fuel rail in the engine compartment got wrapped as well. This was done a few years back and I have not had the issue since but the weather has not been really hot enough and my drives long enough to make a solid confirmation the issue has been solved. Also if you are still running winter grade fuel in the heat of the summer the issue is more likely to occur. I concur that dumping in a few gallons of not warm gasoline will get you going again.
Hi John
Thank you for sharing
I ordered up some insulation and heat shields and will give that a go.
I have poor hot starting too so ordered a fuel regulator to swap over and try. The vacuum hose is so hard I’ll need to replace that too I think.
Will let you know how it goes and if I need to add a cooler too. The double pump looks like a pain to install.
Best
Ian
I have the TSB on the double pump mod and you are right, way too complex (typical Jaguar solution LOL) , and the necessary parts are NLS. Since I was working at Jaguar Land Rover when this was launched I was familiar with the mod.
I tried to find the TSB for it - but as you say the parts they list for sure are no longer available. I was half thinking of adding a second pump in series to see if that helps but that increases pressure not flowrate so might not work- but as yet will hold off until the insulation is fitted - maybe i can make a start tomorrow before the heat arrives later in the week
Best
Ian
Well so far I have insulated the fuel rail - and driven the car in 90 degrees and stuck in traffic in the city for 1hr +
I feel a drop in power at worst but no stalling or total loss of power.
I swapped the fuel regulator - as i have hot start issues - after being stood for an hour say. Didnt change anything. I have fitted a new crank shaft sensor as was told that could cause it.
Any one got other ideas what could be causing the poor hot start?
