I read somewhere in a Volvo workshop document online, where it stated, do not disconnect the cable connector from the coil (referring to individual coils in 3.0 inline six) when removing spark plugs.
Has anyone come across this warning?
960 Spark Plug Removal. [Inquiry] How do I change the spark plugs on my 960? [Responses: Carlos Torres/Tom Irwin/Warren Bain] The plugs are on the middle of the engine.
Remove spark plug access cover. (Black cover on top of engine.)
Once you have the black plastic cover off, number the coil packs with a magic marker 1 - 6 front to back so you can correctly replace them.
Coil packs are held in with a pair of 10mm bolts (A and B in the illustration. Later 960s have only one bolt at A).
Once you have the bolts out the pack should just pull out. A little twisting may help as there is an "O" ring seal at the top of the valve cover and a big boot at the spark plug.
Remove coils from spark plugs. Do NOT disconnect coil wires. (VERY IMPORTANT)
Inspect the condition of the wiring going to the coil pack. Look for crumbled insulation or charring. See 960 FAQ file for information on failing engine wiring harnesses.
If you have comprssed air blow out the plug cavity before you take the plug out. As an alternative use a vacuum cleaner and brush to clean any "stuff" out of the hole to avoid having it fall into the cylinder.
Remove spark plugs. Use a good quality, rubber insulated spark plug socket. Once they are unscrewed, you have to haul them up out of the hole.
Check and adjust spark plug gap to: 0.030" (.75 mm)
Install clean, "un-oiled", spark plugs and torque to: 18 ft. lbs .
Refit ignition coils.
I did this, and after I reconnected it, and started my 960, it ran very roughly and eventually the Catalytic Converter failed and so did the O2 sensor.
Would this have been the cause? I have no idea why it might be the case, but I am investigating all possible causes!