I have a Jaguar XJ6 4.0 litre sport. Lately it has been playing up and misfiring now and then. But I noticed it would fix itself or if I kicked the ecu cover hard it would fix it also. Because previously I had a wiring fault in the ecu wires. So I called the breakdown company and he checked it on his computer with no faults. He disconnected all the coil wires one at a time. When he disconnected the wire for cylinder 5 and 6 nearest the windscreen it never changed the misfire. The guy suggested it could be two coil packs that are faulty which I do not believe is possible at the same time. He never took the plugs out and checked for a spark either. Any ideas would be appreciated.

Mat

 

Sounds like an ECU problem. Report of corroded pins crop up fairly often.





Not that much of a stretch to have two faulty coils. They are a known problem area. But....maybe the ECU isn't commanding the coils to fire?

If kicking the ECU fixes the problem then that's where you need to go first !

Cheers
DD

 

I changed the ecu over and tried another one that is working still the same problem. Bit strange

 

Well, in that case, it sounds like a problem with those two coils or the wiring to them.

I'd remove the two coils for a look-see. Sometimes its just cracked boots....which can be ordered and replaced individually. Other times the coils just start giving out.

If you go to buy coils you might want to read the thread titled "Heads Up On X300 Coils". The bottom line is to buy the *original made-in-Japan coils* if you're concerned about longevity.

Cheers
DD

 

I checked the coil by swapping them round on the engine they was fine. So I took out the ecu checked all the connectors and for any wire damage. Put the ecu back its running fine now.

 

Maybe in moving (unplugging/reinstalling) the coils and ECU you have inadvertently cleaned some connections that had developed a high enough resistance due to minor corrosion to inhibit normal operation.

.

 

My Jaguar XJ6 4 litre sport returns around 200 miles to a full tank around 80 litres is this really bad ?. The trip computer reports it does between 14 and 17 mpg is this normal also. I have checked for fuel leaks it just seems really bad why it is drinking so much fuel. I understand that a 4 litre will use a lot of fuel but not this much. Im wondering if the fuel gauge is faulty. Because when you fill it up the petrol meter needle drops quite quickly even after a short distance. I have done nearly 60 miles and it is showing nearly half of tank of fuel left. Im not sure what to check for. It recently went on a diagnostic computer and no faults. any ideas would be appreciated. Its getting to the point where I will have to stop driving it.

 

Your MPG is fine for that engine I get about 15 but my foot causes this, although when you fill the tank completely topping the filler neck it should hold nearly 28 gallons or about 100-105 litres so something is lying to you either the trip has gone insane or the tank isn't actually being filled fully which I doubt since you filled it. I can get about 300 miles out of mine so something is up.

 

I was under the impression the tank volume was around 21 gal US. But no matter what, we need to clarify whether we are comparing US or Imp. gal.

 

To my knowledge the petrol tank on my car is 80 litres. Which is 17.59 imperial gallons.

 

Matt I can tell you for sure you have something wrong with your car. That fuel consumption is far too high.

I had a 4L sport and regularly traveled from Portsmouth to Newcastle, a distance of over 300 miles, I still had just over a quarter of a tank left.

It does depend on how you drive but for me, it is too much.

Not sure what the answer would be but it needs checking.

Jim

 

Thanks for replying. Do you remember what it was averaging mpg on the trip computer ?.