"Not firing" Just what does this mean?

No spark at the plug? Plugs sparking fine, but an error code is being
stored?

Boxer wrote:           ( 1996 Chevy 454 )

    Cylinders #5 and 6 do not fire.    I changed plugs, wires, cap and rotor.  Compression for
all 8 is good.   There is no change with the 5 and 6 plug wires are on or off the cap.    No CEL.
   Could it be in the fuel system? I would have to remove the plenum to check, it's in a motor
home not much room to work.
  Could it be the cam?  It is strange that it is 5 and 6 across from each other.   Oil seems to
be ok and not full of fuel.  Exhaust seems rich and it is eating gas.    Any ideas?
___________________________________________

Some firing orders such as  1_8_4_3_6_5_7_2  make it easy to
mistakenly interchange the #5 and #6 wires at the distributor
cap.   Confirm actual firing order and recheck wire installation.

___  Dtributor cap shorted or cracked between the #5 and #6 posts.
___  Cap on crooked - rotor is too far from #5 and #6.
___  Vacuum leak in manifold near #5 and #6 intake ports.
___ Two bad individual injectors at #5 and #6.
___ Two bad plugs.     Remove the #5 and #6 plugs, lay them
on a metal engine part, attach the plug wires and crank the
engine.   If there is spark, plugs and wires are probably okay.
___ Probably not the cam because compression is okay.

Good luck.      Rodan.
____________________________________________________

===  5 and 6 were not firing before new ignition parts were installed.
===  Distributor cap is the new type and has the evens on one side
===  and odds on the other with the corresponding # on it so I am
===  sure they are correct.

You don't know that they are "not firing", because you
have not taken those two plugs out and visibly observed
the sparks.   This is the first (and zero-cost) test needed.
Then you can decide what further action to take.

===  The manifold has 2 rails feeding the cylinders.   It doesn't
===  have individual injectors.  It could be a bad rail or tube?

If there are injectors, a couple could be dribbling fuel.
Fuel rails feed smaller tubes that usually go to injectors.
Sorry, I have no experience with tubes that don't end
in fuel injectors.

===  Where would I check for a manifold air leak between 5 and 6
===  or should spray WD-40 there and listen for a change in rpm?

It is a small probability of the cause.  I meant a big vacuum
leak, like a brake vacuum port in the manifold left open.

Notes

Another possible cause: a sloppy bearing in the distributor that
lets the shaft lean off-center, so the rotor passes too far from
the #5 and #6 terminals.

A flat cam lobe, a burned valve, a bent pushrod, or broken piston
rings could cause misfiring, but you confirmed that compression
is acceptable and uniform, so the problem must be elsewhere.

Good luck.      Rodan.