hi all , i'm new here , i have a question about my car and wondering has anyone experience of a similar issue ?
i have a 2004 xj6 3.0 , when going up a slight incline , steady constant speed , under load there is a sensation of a gentle misfire , going into kickdown and speeding up gets rid of it , has anyone else had this ? am i suffering engine issues or gearbox issues , thanks

 

Air leak or (perhaps more likely) bad coil(s).

Check for codes & pending ones. Check fuel trims.

 

 

I had a very similar symptom of a stumble while going up inclines, after a long time of no codes and no abnormal fuel trims, I was able to see dropouts in my fuel rail pressure sensor readings. Thread here: https://www.jaguarforums.com/forum/x...-195311/page3/

Of course I don't suggest throwing a $120 sensor on the car without checking things carefully. As mentioned, issue could be spark, vacuum leaks, or any number of other things.

 

 

What I was seeing on my scan tool was: under steady cruise, encounter a slight incline the FRP (fuel pressure @ rail PID) would "spike" down to approx 10psi (several times) then back to to 50 psi as normal. It was accompanied by the front O2 sensors pegging rich, which caused the stumble. My best guess is the FRP sensor was dropping out momentarily, causing the PCM to speed up the fuel pump to compensate. This caused a massively rich condition that both the O2 sensors responded to.

Normally the FRP sensor will move around between 40-60 psi depending on engine load and rpm. But normally will never dip down to 10 psi. It was also a very short burst, not like it dropped down to 10 psi continuously, just a quick dropout.