Hi. I could not not find a thread with a similar problem. Hence posting a new one.

The fuel indicator suddenly/immediately falls to EMPTY when the gauge measure comes below the half. The range immediately becomes 0KM from around 200KM. After this when I fill in only around 5 litres of the fuel (and the total tank capacity is approx 58 litres), the gauge jumps back immediately to around half. After this when I drive a few miles, the gauge falls back again.

I noticed that when the tank is fully filled, it shows a range of approx. 460 KMS. But the car stops dead at around 310 KMS with the behavior of the gauge.

With this behavior, I think the fuel is still in the tank, but for some reason, it is not sent/pumped to the engine (or something like that) after it reduces to particular level.

I have explained the issue in layman terms. Why is this happening, what can be wrong and how best to check it, and how best to resolve it ?

 

An update...

After the gauge falls down to EMPTY, it randomly goes back to its normal position as per fuel balance in tank, and again falls down to EMPTY. This happens for 1 or more times after the misbehavior starts.

 

I filled in 11 litres and the indicator goes back to above the half, and I drive again for 100km. After this, as the indicator goes to 45-40%, it falls to 0 again. So I filled in another 11 litres of fuel and it goes back to 60%. (definitely, the tank capacity is not 20 litres ?!?)

Anybody here to advice please.

Thanks.

 

It's a guess which part of the car is bad but sounds like the sensor(s) for fuel level and/or wiring etc. (Suspect computers last - they rarely fail.)

 

jagnew ,

From what I can understand the engine cuts out at below half tank , also to this
the fuel gauge level drops to zero , I am assuming you have the petrol model .

I would start with the fuel tank sender unit , have it removed and tested , although you appear to have two problems they could be related .

XJ6 & XJ8 2003 - 2006 do have , I'm sure an " IN TANK PRE - PUMP " ( part number I believe is C2C24164 ) .

The pre pump was needed to maintain a continuous supply of fuel to the main fuel pump .

The main fuel pump , because of its location can't draw enough fuel from the tank when the level is below or less than half tank .

This is not limited to Jaguar , most fuel injected cars have them .

As the pre pump is attached to the sender unit , it would be recommended to replace them as a whole , ie pump and sender as one , that is , " if the pump or sender unit turn out to be faulty " .

As you can see , this is not a DIY job and you should NOT ATTEMPT to do it .
Sensitive testing equipment is need , but more importantly the fuel tank and it's contents is extremely volatile and dangerous .

As I said this is where I would start .

Good luck with that

 

When I bought my XJ6, which was running BADLY on LPG. I started using petrol only.
I then realised the guage was not working correctly with similar symptoms to what you describe.
I stripped out the pump and senders, yes there are 2 one on each side, and quickly realised that something was missing.
This was a pipe which is called I think a Jet Pump which is essentially a syphon hose which draws fuel from the drivers side part of the saddle to the other where the pump is. The previous owner must have had a problem and as he was running LPG decide to do without it.
I had nearly half a tank of fuel on one side which was not useable and probaly stagnant?

In essence I am saying it sounds like your jet pump is not working?
I replaced both senders as a unit with 2nd hand one and have now got normal readings and a fully usable tank

 

Thanks to both Mastersid and Joesoap.
Yes, its a petrol model.

I take your advice. As you said, this can be volatile. This has to be done in a proper garage environment by the professionals. My only concern was how best to detect the issue without much beating around the bush.

In the 2 advises above, is the PRE-PUMP and the JET PUMP the same unit ?

Any idea as to how much did the 2nd hand cost, and how much would be the new unit ?

Can you help with the part number of the sender unit as well.

Thanks to both.

 

The 2nd hand one was £40 from breakers which I stripped out: have seen them on ebay for simlar money.
as an engineer I was comfortable doing it myself but it isnt difficult. Getting the seat base up was most difficult bit until I trawled the forum!!

The unit I got was from an S type although there were marginal differences, may be closer if from 2004 onward?

Where are you based I see its an XJ6 so guessing you are UK?

 

Seem to remember that a lot of level faults were caused by dirty tracks on the sender units and there are tests giving resistance range from emppty to full.
Also remember some type of dash fuel tank check/reset. although being too close to retirement and too fond of changing cars could be mistaken and confusing with another make.

Hopefully some of the experts can confirm one way or the other.

You should download JEPC from forum, it is an excellent tool giving part numbers and drawings for all models.

 

just saw both pump/sender and sender on ebay from x350 xj6 you could buy and have indy fit them?

 

Jagnew ,

If you can , try listening carefully , you may hear the fuel pump buzzing louder than normal , that's because it's working flat out to supply fuel to the engine without the help of the tank pre pump.

Apart from that there really are no short cuts , the fuel tank sender unit with the pre pump needs to be removed and tested , no big deal really .

Never heard of the term " JET PUMP " however , given that it's described as being in the fuel tank , I would say it's the same thing .

Your VIN number will determine what part numbers you need and how much they cost .

As joesoap advised , you should download the JEPC to find what you need .

As an example , according to SNG Barratt Jag Parts , you could spend up to 513 .00 Pounds for a NEW fuel tank " sender unit with pump assembly " .

Again good luck with that ,

 

JEPC calls it JET Pump:
part no 5 in fuel tank: G00472 to H32732
PART C2C31126?
Still think second hand is way to go new prices are waay too expensive for 12 year old car

 

Can you get 'Engineering-Mode' in the INSTPK display to see the level of the right and left sending units??????

The Jet Pump might be faulty but maybe the sending units are functional???

bob gauff