I have a 2006 X-Type Jaguar. For a long time it would periodically start to jerk and slowly lose power until it would cut off or I would have to switch it off and then it would start and go for a while before it started this again. Then it would be fine for a period. Each time that I took it to the garage it would be going fine and they could not find a problem.
After a major service where they replaced the fuel lines and the fan, it stopped doing this.
But when we went on a trip, after about 100ks it started the same problem. A garage en route to our destination replaced the fuel pump but after 50 ks it started the same problem. This has now become much worse and it will only drive for a kilometer or two before starting the stuttering and losing power until it cuts completely. It has now been with the dealer for three weeks and they have not been able to diagnose the problem. Help please!

 

Is there a fuel filter in line somewhere?

 

Diesel? Gas/petrol? Engine size? Any codes (OBD)?

 

By "no-one seems able to diagonise" (diagnose) - it sounds like not many if any competent techs have tried. So either DIY or find a competent one.

 

Another possibility is the cats collapsing.

 

Jeni, I want you to try something for me. Get the car started up and then turn on the headlights, the dash blower (fastest speed possible), rear defroster, and seat heaters. Let the car idle for either 5 minutes or until the car starts to really run rough. With the engine still running, open the hood/bonnet of the car and pull the cover off the top of the battery. I want you then to cup your hand (DO NOT!!!!! let it touch) over the battery terminals one at a time. Do both feel about the same temperature as the other parts under the hood/bonnet? If so, then odds are you are looking at a bad catalytic converter. If one of the battery posts is hot (like you think you could fry an egg on it hot), then you have a bad battery cable and what you are seeing is the lowering voltage is causing the components of the car to start running slower. This will cause the fuel pump to not put out as much pressure, leading to the engine loosing power. If you have a higher end code reader, most of them will let you see various parameters of the car as the computer sees them. You can then either watch voltage or fuel rail pressure. You should see the battery voltage be up around 13.7 VDC (may be as high as 15.5 VDC right after starting the engine). If you are seeing it down around 12.6 VDC or lower, then you have either a problem with the alternator or the battery cables are going on you. Odds are it is the battery cable(s). If you are looking at the fuel rail (assuming you have a petrol/gas vehicle), you should see the fuel rail up around 40 psi. If you rev the engine, you may see it rise slightly (up to say 45 psi). If you turn on the car (to the RUN position) and do not start the engine, then it should be up around 50 psi.

Let us know what you find. People like me keep track of problems that members have and use that information to troubleshoot other vehicles by knowing what the likely failure modes are.

 

Dear Steve,
Jaguar finally came back to me today and said that the problem is the fuel pump - it is a universal pump but it has to be the Jaguar pump which has a sensor to interact with the computer. I truly hope that this is the problem as it has cost a fortune.

 

If the problem has not been resolved yet you might want to do thermo's test if you can.. the new pump could suffer the same fate