Ok the super Volvo has been taking Son to College more or less.  He parked it at home and the next morning it would not start.   RRRRRRR  turns over and miss fires a little.  Like the timing belt slipped or its not getting any gas.   I check everything and it seems OK.  When  I look in the fuse panel.  it seems more empty than usual.   I think the fuel injector relay is gone.   AM I missing something in here?   SC

i wiggled things and checked the sparkplugs  and it started,  Horray,     ran rough,  I disconnected plug wires and discovered  the #3 plug wire made a difference and it starts and runs better  with no # 3.  does that test say the distrubute cap is arcng?  Maybe?   or maybe that cyl  has no compression?.  I'm also thinking head gasket leak due to some water out the tail pipe.  Happy Thanksgiving.  SC

whats odd is it runs real bad untill I pull #3 wire off the plug.

whats odd is it runs real bad untill I pull #3 wire off the plug.

Maybe you have two plug wires crossed and one plug is fouled out.  If #3 is firing at the wrong time (let's say, about halfway through the compression stoke) and the other crosswired cylinder is just a dead skip, it would smooth out considerably when you pulled the #3 plug wire and made #3 a dead skip as well.  Depending on their position in the firing order and # of cylinders, it could run very smooth with two dead cylinders.

Changing the plugs around did not do in anything.  I pulled the dist cap and rotor.  The rotor has a a hole wallered in it,  or maybe that is how it it supposed to be.  none of the pics I see of new ones have a dent hole in center.  maybe I'll change it

The cap is new,  very pretty,  I just removed the timing belt and reinstalled.  it is spot on.  Car starts Ok as long as #3 is unplugged.   I can't figure out why #3 is fighting the engine when the plug is hooked up. 

I wonder if a valve spring collapsed,  or a valve is stuck closed,  Could that make a cyl fight the engine when its spark plug is firing?

Could something make just one Sparkplug fire wrong?  Maybe Crank POS sensor?

No CEL codes

What a holiday.  I ran a compression check.   Turns out #4 is at 50 psi.  The engine runs ok as long as 3 or 4 plug wire is off.  I can't figure out why that is.   Maybe #4 exhaust valve is not closing.  the other 3 clys have 150 psi

You may try a wet compression test on 4,  put a very small amount of motor oil in the cylinder,  maybe a thimble full,  then do the compression test,  if it goes up it may be the rings or the cylinder washed down by some thing like a leaky injector or a fouled plug letting gas ino the cylinder,  if not probably a valve or head gasket, the heads or not to bad to pull on that motor