Before the job of emission controls, lead-free gasoline and clean burn engines, spark plug maintain (cleaning, space checking and replacement) was a typical practice. Spark plugs would come to be dirty end a fairly short duration of time (~15,000 miles) from the command in gasoline and also the carbon indigenous incomplete combustion. In addition, the facility electrode would certainly burn away, raising the plug gap. Failure to keep spark plugs clean would lead to performance and starting problems. Spark plug maintain was a severe matter.

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But, together engine control technology progressed, spark plugs remained cleaner for longer periods the time, reducing maintain tasks and extending organization life. Anyone was amazed as soon as the instead of cycle became 30,000 mile or 60,000 miles, or the unthinkable 100,000 miles! And, as soon as the plugs were ultimately replaced, the plugs were frequently clean however with burned electrodes. The shed electrodes would an outcome in excessively vast plug gaps the would cause performance problems.


From a maintain standpoint, it’s vital to understand which hemi V8 engine is in the auto being serviced.

Not just are the service intervals for replacement different, but not all hemi engines usage the very same spark plug. That’s an essential point because some room a traditional thread design and some are tapered object (see Figure 1). This two different designs room not interchangeable. Installing, or rather trying to install, the wrong format spark plug can damage the spark plug and, quite possibly, the subject in the cylinder head.

The 5.7L spark plug is a traditional style with straight threads. It’s also nickel-plated. The 6.4L SRT engine plug has tapered threads and has a platinum resistor design. The resistance values variety from 3,500 come 20,000 ohms once checked with at least a 1,000-volt tester. Execute not usage an ohmmeter to inspect spark plug resistance as an inaccurate reading will result.


There are two spark plugs every cylinder in a hem V8 engine. So, once the plugs require replacing, there are 16 to change, not eight. Also, it must be provided that all hem V8 engines usage coil-on-plug ignition systems. All except the 2004-2005 engines, the is. Stop look in ~ that system in some much more detail together replacing spark plugs ~ above this architecture is various than the procedure for coil-on-plug.

The at an early stage 5.7L hem V8 engines room equipped with eight separate and independent ignition coils. The one-piece coil bolts directly to the cylinder head cover. The attaches the secondary output terminal directly to the spark plug utilizing a rubber boot seal. Every coil has a second output terminal. The second terminal connect a conventional spark plug cable to a spark plug on the opposite cylinder bank. A separate primary electrical connector is used for every coil.

The spark plug cables that connect the coil come the spark plug on the contrary cylinder financial institution are placed and routed in a distinct plastic loom to keep the cables separated. The loom is clipped to the intake manifold. To protect against a mismatch that cables, a matching spark plug/coil number is displayed on every spark plug cable. These numbers are situated on the peak of the input manifold come the right of the accelerator body.

Now, let’s testimonial the procedures to change the spark plugs on the 2004-2005 5.7L hemi engine … eight of the 16 spark plugs are situated under one ignition coil, those coils will have to be removed.

Before remove or disconnecting any kind of spark plug cables, keep in mind the initial position of the cables. Remove the cables one at a time. Spray compressed air into the cylinder head opened for every plug. This will avoid dirt native entering the burning chamber. Eliminate the spark plug.

Check the spark plug void on the brand-new plug (see Figure 2). Be certain the gap meets spec. Special care should it is in taken as soon as installing the new spark plugs right into the cylinder head spark plug wells. Begin the spark plug threading into the cylinder head by hand to avoid cross threading. To help installation, to the right a item of rubber water tap to the brand-new plug. This plugs space a torque-critical design, so carry out not exceed 15 ft.-lbs. Of torque when tightening the plugs.

Install the spark plug cables. Use dielectric grease inside the boots to aid installation. To stop ignition crossfire, the spark plug cables must be put in the routing impend in the initial positions. Install the ignition coils to end up the installation.

For all hemi V8 engines developed after 2005, spark plug replacement is a bit much more straightforward. As mentioned, this engines are equipped v coil-on-plug ignition systems. First, eliminate the engine cover. Then, disconnect the ignition coil cable harness connector. Remove the 2 ignition coil bolts, then, with a slight rocking motion, eliminate the coil (the rubber boots space integral through the coil).

Install the brand-new spark plugs. Start the spark plug threading right into the cylinder head by hand to prevent cross threading. To help installation, to the right a piece of rubber water tap to the brand-new plug. Tighten the spark plugs come the appropriate torque:

5.7L engine – 18.5 come 22 ft.-lbs.

6.4L engine – 7.5 come 15 ft.-lbs. (do not exceed 15 ft.-lbs.)

Install the ignition coil. Repeat in the very same manner for the various other seven cylinders. Install the engine cover.

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Note: always tighten spark plugs to the specified torque; excessive or inadequate torque will reason damage to the cylinder head or spark plug.