My previously very reliable 2003 XJR got unreliable the other day. Before I have it towed to the Jaguar dealer I thought I would see if anybody in the group had some ideas on what the problem might be.

Here is the situation; after leaving work, I made several stops on my way home. After the fourth stop, started the car and it ran very rough. Pushing on the gas pedal did nothing. Turned the car off, started again and got same result. Put the car in gear and it would move, but mainly under the engine torque, the gas pedal had little effect. Had the car towed home. The next day check to see if it was throwing any codes and it was not. Now it will turn over but not start. Checked the fuel cut off switch thinking the angle of taking it on and off flatbed may have trigger it, but it was okay. Disconnected the battery for a few minutes to see if they might cause a reset, but no change.

The car has just under half a tank of fuel, and just over 60,000 miles on it.

Any ideas?

Submitted by jcc@majure.com on Thu, 03/15/2012 - 08:09

Thought I would follow up on this thread in case anyone was interested. The problem with the car running rough, then not starting was due to a bad low speed fuel pump. (The XJRs and SuperV8s have two pumps.) Replacing the pumps, both at the same time is recommended, involves taking out the fuel tank which is in the trunk behind the back seat. The pumps are about $200 buck a piece; pulse the filters and $100 sensor wire that goes with it. - Ugh! I am very fortunate in that I have a lift in my garage and a mechanic that works for Jaguar and does work on the side. My total bill was $750; I would hate to think what the dealer would have charged. Hopefully that old Jaguar unreliability is not creeping back in as the car only has 60K miles on it.

Submitted by stevejag@sbcgl… on Thu, 03/08/2012 - 12:26

What you describe sounds like a throttle body failure, up to the part where it won't start. If a throttle failure occurs there will be virtually no throttle response to the pedal, and it will usually idle very rough. That kind of fault probably WILL NOT be read by a generic scantool, it just can't register it because it is a 'manufacturer' specified fault.

I have seen a throttle body cause a no-start, but that is very, very rare.

Your best bet is a trip to the dealer or someone that has dealer level diagnostic equipment.

Good luck!