Tools Needed

You will need a 3/8” drive ratchet with a 10mm
socket and 5/8” or 16mm spark plug socket. A
spark plug socket has a special deep well
design and a rubber insert to protect the
ceramic plug body from cracking during
installation. You will also need a 6” or so
extension. Make sure to have some Never
Seize on hand. A spark plug gap measuring
and adjusting tool is also needed. A torque
wrench is optional.

Precautions

Even though this is an easy job, almost a fool-proof job, you can make a few big mistakes. First,
always wait for the engine to cool before changing plugs. The aluminum heads on this motor expand
at a different rate from the thread inserts and the spark plug threads. If you change the plugs while
hot, you can end up pulling out the thread inserts or gouging the threads. Second, ALWAYS use anti-
seize on the spark plugs threads. Failure to do so may cause the steel threads to seize in the thread
inserts. Finally, ALWAYS start threading the plugs by hand and run them in by hand (i.e. no ratchet
and NEVER use an air ratchet at all!) as far as they will go.
IF you do a lot of off-road driving, you may find that there is a lot of sand or other debris on the valve
covers. It is VERY important that you blow or wash the valve covers off prior to pulling the plugs.
Procedure
The process is the same for each of the 8 plugs.

1. Start by checking the gap on the new plugs.

The specified gap is .032 inches for our 4.7L V8.  
To find out what it is for a V6, or more information, check out the NGK website.

I found the Iridium plugs came pre-gapped at about .030.

The old plugs had a gap between .035 and .038.
That alone is a good indication that the old plugs were worn.

To check the gap, insert the proper thickness feeler gauge between the side terminal and the center wire. If the gauge
slides in with slop, the gap is too wide. You can gently push the spark plug electrode against
the bench top or whatever to close the gap. Most sparkplug feeler gauges have a notch in
them used to “grip” the electrode so you can bend it out or in. If the feeler won’t fit in the gap,
you’ll have to spread the gap. If your feeler setup doesn’t have the notch described above, you
can use a thin flat-blade screwdriver; just don’t pry against the center wire (Pictures 2 & 3).



2. Coat the threads on each plug with a small amount of anti-seize. Make sure to keep the anti-
seize off the electrode.



3. We are now ready to R&R the spark plugs. You might want to work on once cylinder at a time.
Make sure to clean off any debris from the top of the valve covers. We don’t want any dirt or
sand getting down the spark plug tube. Begin by removing the single 10mm bolt holding the
coil pack to the cylinder. You don’t need to disconnect the wire harness from each coil pack,
but do note that the coil pack wiring is also connected to the injectors. So, when pulling the
coils out, make sure that you don’t put a strain on the injector wiring. I pulled on the main
harness to get the slack needed to pull the coils out. On the passenger side, I unbolted the
injector/coil harness from the intake manifold to get the slack needed.



4. With the coil removed, look down the plug tube and make sure that there is no debris or sand
that might fall into the cylinder when the plug is removed. Attach the extension to the 5/8” plug
socket and ratchet and remove the plug. Pull the plug out of the hole. The plug should “stick”
in the rubber in the socket.


5. Inspect the old plug carefully (see Picture 3). You are looking for oil on the body of the plug,
damage to the plug threads, damage to the electrode, or deposits on the plug electrode. Oil on
the plug body indicates that the valve cover seal is leaking. Consider replacement. Damaged
threads or a smashed side terminal means your day is over. If you can, get the plug back into
the truck and drive to your favorite repair shop (assuming the truck runs). Deposits on the
electrode need to be diagnosed. Oil fouling is a sign of bad valve guides or piston rings. Green
or red liquid on the electrode indicates a possible head gasket leak. The electrode should be a
light tan or gray and intact. If not, consult a service manual to diagnose the problem.


6. Put the new plug securely into the plug socket. Test to make sure that the plug does not and
will not fall out of the plug socket when the socket is flipped upside down. Using ONLY the
extension, hand-thread the new plug into the hole. It should start and thread in very easily. If
not, thread back out and try again.


7. Once the plug is all the way down, torque the plug by turning the plug about ½ turn. I find it
easiest to do two ¼ turns. If you have a torque wrench, torque to 13 ft-lbs.


8. Place the coil back in the hole and make sure it seats properly. The contact in the coil sleeve
is spring loaded to ensure contact is made once the coil is tightened. Tighten the coil pack
bolt.
That’s it. Do this 7 more times and you’re done! Fire up the truck and make sure all is well.
The V-6 service is the same except that plug wires are used instead of the coil on plug arrangement.

Troubleshooting
It’s uncommon to have problems on a job this simple, but some things can go wrong.

1. Plug is stuck in the cylinder. Each plug should come out easily with a 3/8” ratchet. If not, the
plug is seized in the cylinder thread insert. Go see a mechanic.


2. Plug unscrews but won’t come out with the socket. The rubber insert in the plug socket is
worn, greasy, or just too loose. You can use a section of rubber fuel tubing to “grab” the plug.
You can use this same tubing to hand thread the plugs during installation.


3. Plug won’t hand thread into the cylinder. This typically happens if the plug socket is in bad
shape and wont hold the plug square in the socket. The plug needs to be perpendicular to the
cylinder head/valve cover. Again, consider using a length of rubber fuel line to thread in the
plugs. Avoid using “wobble” socket extensions.


4. Plug threads in but will never get tight. This is a bad sign, usually the result of stripped threads.
Pull out the plug and inspect the threads for damage. If the plug threads are OK, look down
the plug tube and examine head threads. If they are damaged, consider getting a plug thread
chaser from the parts store. If that doesn’t work, put the plug in as best you can and go see a
mechanic.


5. Engine has a minor misfire not present prior to changing plugs. There are several possible
causes. First, there may be contamination (oil or anti-seize) on the electrode. Remove plugs
one by one and check for contamination. One or more of the plugs might not have been
tightened properly. Back each plug out until loose, hand tighten, then tighten with socket
wrench ½ turn. One or more of the coil on plug assemblies may be loose or the wiring may
have come off. Check each assembly for proper installation.


6. Engine has a MAJOR misfire. Two of the coil on plug assemblies have been installed on the
wrong cylinders. If you do one plug at a time, this is impossible. Examine the wiring harness
and make sure that each coil plug is also connected to the injector for the same cylinder.