Hello Everyone,
I am experiencing misfires on cyclinder 7 with new coil, new spark plug, Air Mass cleaned, Noid Light indicating power to fuel injectors, and fuel injectors having been just cleaned and tested with no failures in mechanical operation or spray patterns.

1. I need to ask from anyone what the steps are once you have shut off the fuel delivery system and removed the first spark plug. What should I do next and look for?

2. How do you achieve a full throttle open state for testing compression...have someone hold down the accelerator pedal?

3. Dry Test and wet test procedure explanation, which is done first?

4. Range of compression PSI for 86K 1999 XJ8 4.0 non-aspirated?



Thank you for your kindness!

<<<Mathew>>>

 

Easy to pull the fuses. Fuse 7 in the trunk (boot) fuse panel is the fuel pump relay as is fuse 22 if you have a SC model.

I have always used the big end of a screwdriver to hold the butterfly open. Not 100% open but close enough.

Something over 155psi would be wonderful. Issue is the difference between the high an low cylinders.

 

You should do the dry test first.

FWIW compression seems to range from 180'ish on younger motors to a minimum of 140'ish on older good running cars.

Here's a thread I did on diagnosing hesitation, stumble, miss:

https://www.jaguarforums.com/forum/j...agnosis-52294/

Good luck,

Ken Wolkens

 

I am having problems finding a compression gauge to use that has an extended pressure tube to reach down into spark plug opening. Can anyone suggest what they use? The ones I have seen have a short adapter and then a flexible hose, which I didn't believe could be used.

Any thoughts?

Thnak you very much!

<<<Mathew>>>

 

Here's the craftsman gauge I've used for over 25 years. It may not be pinpoint accurate like a snap-on but it's close enough for anything I've ever needed.

Craftsman Compression Test Kit : Sears Outlet