Hi all

I have a very strange problem and it has me stumped... My car is losing a lot of fuel, and it's not coming out the pipes for that matter, it appears that is is evaporating... To put the picture out there, she has lost a couple litres (just under a gallon I'd say) from merely standing a few days...

There is absolutely no smell of fuel and no drips on the driveway...

Is anyone familiar with any breathers for the fuel tanks etc? I'd love to know where any breather pipes are and where they are meant to go...

Any other ideas are welcome, the fuel consumption alone is enough.

Many thanks.

 

There really isn't anywhere the fuel could be hiding...
The breathers (technically vapour canisters) are in the C posts, and the vent pipes run towards the right side of the car, and into the carbon canister in the fender well...

I know you mentioned before that you had a T in the boot... Are you sure that you are loosing fuel vs the tanks just equalizing over night?
In other words, If you have a quarter tank in one, and three quarter in the other when you park it at night... do you have half a tank in each the next morning?

Cheers
David
shop.everydayxj.com

 

I am sure that the fuel is equalizing, but also evaporating... Interesting you mention the vapour canisters in the wheel well... I've got 2 pipes emerging from the wheel wells that vent to atmosphere plus another small one that comes out just behind the rear axle, I havn't checked where it comes from, but at times I can visibly see vapours escaping through it...

Are the pipes sticking out the wheel wells meant to go to atmosphere?

Thanks for the reply David.

 

Those are water drains I'm looking at, the ones in the wheel arches, sorry.

Still not sure why fuel appears to be evaporating though... Unless my gauges are having a tizz...

Still strange to have fuel one day and no gas (she wouldn't pull away) 3 days later...

 

Gotta ask to eliminate:
Caps locked?
Car in secure area?
No sign of siphoning?

Are you talking a small drop in the guage readings, or a BIG drop (like half a tank). I don't know your enviromentals where you are, but I know temperature can make a difference to the density and volume of petrol.
Also, My guage can vary by 1/8th of a tank just by the position it is sitting, and weather it is running or not etc... The guage and senders are decades old, so not as accurate as todays versions.

Question to everyone: Is it possible to dip the tanks on a Jag? If so, and this seems to be an ongoing thing, try dipping (clean marked dowel rod??) and recording levels that way. See if you are actually losing, or just gremlins in the guage

Just my thoughts on the matter, keep us posted :-)

 

Many thanks Richard, I shall try that! Very good idea! Now why didn't I think of that... Yes probably just the temps then... Plus I am parked on a slope (no shelter until I'm out the house).

I always wondered how she managed to not use any fuel while I was driving...

I'm talking about a small drop though, like a 1/10th of a trank...

 

How much of a slope are you talking?
I know your car has had some modifications.. One common one is to punch a hole through the one way valve at the charcoal cannister to help relieve fuel tank woosh.... One drawback to that is that fuel can siphon from the tanks into the charcoal canister (or beyond)...
I'd be tempted to check the one way valve to see if it's functioning, or if there is dampness in the lines going to the charcoal cannister....

David

 

Three contributions:


1. Leaking injector/s. Overly rich run on start up?
2. As David says, is the fuel vapor canister under the front wing saturated. The engine is to purge that.
3. I/ve never tried to dip my Jaguar tank. The term also used is stabbing. In olden days, a wooden rule was standard in cars sans gauges! I have tried to get a siphon hose in with no luck?


In olden days, kids were know to carry around a bit of garden hose and get gas at
the mid nite station. Next door to mid nite auto supply.


Carl

 

I filled each tank to half, suddenly lasts much better... My guess is that the last 8th of the tank disappears quickly off the gauge due to the shape of the tank, the slope of the driveway / parking bay does make a difference though, mine must be a good 5 degrees... The modifications I am not sure of, worth checking, thanks David.

I have had success, Carl, with a siphon hose, I think you need to angle the hose towards the rear of the car, if that's what you're trying to do. Not too sure if a rigid wooden rule will work as well though.

Thanks everyone.

 

David, I eliminated the check valve in my 1984 XJ 6 back in 1992 to eliminate the woosshh (vapor pressure buildup at the tanks), a trick shown to me by a Jaguar mechanic which I continually pass around in this forum.

I used a plastic connector to replace the check valve and splice the hose coming from the tanks and the hose going to the charcoal cannister.

I have not had any syphoning of liquid fuel through this line by eliminating the check valve. Quite the opposite in my experience, the vapor buildup woosshh dissapeared, no fuel odor, no after-effects.

I did have a leaking tank as you know, but not caused by eliminating the check valve, it was a bad seam at the tank.

 

"I have not had any syphoning of liquid fuel through this line by eliminating the check valve. Quite the opposite in my experience, the vapor buildup woosshh dissapeared, no fuel odor, no after-effects."


I've drilled a few of those one ways valves out myself with good results.... I think the reference to syphoning is based on parking on really steep inclines (think parallel parking in San Francisco)... Think it was something that I read on JagLovers a long while ago.... Not based on my personal experience.........

David

 

ohh I see, parking the car facing downhill? then I can see how liquid fuel could find its way downwards.

 

SF is weird in many ways, but the laws of physics have not yet been repealed, yet...
No doubt some politico there may try it.


It isn't the "one way" valve that is the issue under one parking condition. At lweast not to my knowledge.


Tis the practice of eliminating the valves that govern the tank choice. The tanks are simply "tee'd" together. Works just fine, except!!! Park on a steep hill nose to curb. One tank low and one tank high. Fuel goes from the high to the low. If not enough space in the low tank, out the cap. An open invite to miscreants. Torching cars there is a 'sport'!!


So far, so good, my car's fuel system does what it is supposed to do as it came....


Off to the Barber for a much needed shearing.


Carl