I have been having a problem with 96 XJ6, where it runs rough, similar to a cylinder that is not firing up to about 2000 rpm, then just like someone threw a switch, it runs smooth as silk. Another forum indicated that there are two fuel pumps on these cars, a primary and secondary. Could this be my problem?
Thanks!
David

 

Only 2 fuel pumps if it's XJR, 4.0 supercharged... And the second one kicks in at higher revs to prevent fuel starvation when supercharger is spinning like mad. So if it's just naturally aspirated engine, then no, it's not your problem. Go through previous posts, there were loads about misfires and rough operation.

 

As Firecrow states, only 1 fuel pump if it's a normally aspirated engine.

The problem could be caused by so many things, (TPS, vacuum leak, MAFS, ECM, O2 sensors, evap system, EGR system, etc, etc) the best thing to do right now is gather data. Do you have a scan tool device? This will tell you if the car has set any trouble codes (even if the check engine light is not turned on). It will also be able to give you live data that can show the the performance of many of the engine elements that can affect poor running. Without at least some basic data you will end up just throwing parts at the problem which can get very expensive and may not even solve the issue. A decent scan tool can be had for less than $50. Armed with that and a multimeter you can do a good bit of sleuthing.

If you report back here with more info, I'm sure members will be able to give you solid direction. Many of these issues can be tricky to diagnose.