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Thread: Jag X300 hard tp start and stumbling when pulling away

  1. #11
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    I was not aware of the fact that a new coil may be damaged. I still have an old one or two, so I will replace it. Or, I can swap coils on cylinders 3 and 4 for example and see if the misfire transferred with the coil. I also use injector cleaner every so often, but I am not sure about its quality. Is there anything you would recommend? Again, thanks for advice.
    All best, Michael.

  2. #12
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    Hi Michael. I would be inclined to swap coil 3 with one of your spares & see what happens. If you swap 3 with 4, then you would need to connect the car to a diagnostic computor to see if the problem has moved, & that means a trip to the garage & a bill. The coils are easy to change. Just remove the cover on top of the engine, unplug the wires going to the coil, remove the two bolts & lift the coil out. Rember though that Jaguar number their cylinders from the back to the front, so 3 is the third from the rear.
    With regard to the injector cleaner, I do not know if the brands available in Australia would also be available in England. I would just get one that comes from a reputable company. On most, they advise adding half a bottle to a tank full of petrol, however, they usually also say that a full bottle can be added to the tank if the injectors are suspected of being very dirty. Hope that helps. Best wishes, Craig.

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  4. #13
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    The car is currently at the mechanic, with the pump being replaced, and few other minor things on the list, so I will just ask the man doing it to deal with the coils. I like getting my hands dirty with this car, but it just seems reasonable to let him do it
    All best, Michael.
    PS. Good tip with the cylinder numbering.

  5. #14
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    Quick update.
    Changing the fuel pump did help with regards to acceleration and revving ability. However - there is another issue. After driving for 5-10 minutes, the revs dont drop below 1300-1500 rpm when gas pedal is released (unless I use the brake of course) and when i want to accelerate a bit harder, the revs immediately drop by 300-500 rpm for a second, and then the car accelerates normally after two seconds. When I accelerate gently in a linear fashion, it will go to 6k rpm with no issues. When I stop the engine and restart right after, everything is fine. This is quite scary on the big intersections when dynamic start is sometimes necessary.
    Another thing is the fuel consumption. Driving gently in the city will average 20 liters/100km. Driving like a lunatic will average the same.
    What I have noticed is that the there is a big pressure buildup in the tank. When I unscrew the cap, the air/vapour escapes the tank with considerable force. And yes, I am sure the air escapes the tank, not the other way. Now I have started looking at the whole EVAP system. Investigation continues...

  6. #15
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    That is curious. If you think that the problem is caused by excessive pressure in the fuel tank, I would suggest removing the fuel cap & going for a drive to see if that helps. If not, then I would take the car to a specialist Jag repairer/dealer who has the Jaguar diagnostic computer & check for faults. The car's diagnostic system is not foolproof, but there could be a stored fault. If not, the dealers computer may well find something. It rather sounds like a problem within the throttle mechanism, but it may also be a problem with the sensors in the exhaust system. Rather unfortunately, the emission control mechanisms are so complex these days that there are a number of small gadgets in that area that can play up & cause strange problems. Best of luck with it. I well know what it is like to drive a car that you feel is dangerous. Craig.

  7. #16
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    Yesterday I have decided to open the hood and manually open the throttle to see if the problem is located around the throttle body. Of course I did that when the car was playing up.
    I have rotated the TB slowly, and the car was revving fine. But when I did it faster, the rpms dropped as usual, but I also heard a strong hissing sound just before the rpm drop. Hence, I suspect there is a vacuum leak somewhere. It all makes sense. The crack/gap is so small, that its not noticable when driving smoothly. But accelerating harder (regardless of current rpms) makes the gap bigger which spoils the air/fuel mixture and gives wrong data to o2 sensors. I will investigate that further during the weekend. Seems like the pressure buildup in the fuel tank is a separate issue, hopefully solved with new Rochester valve. However, next week the car will be checked properly by a Jag Specialist. Of course I will report the results.
    Thank you Craig for following the thread, it is somehow comforting to know that someone is interested and willing to help.

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