Before the days of emission controls, lead-free gasoline and clean burning engines, spark plug maintenance (cleaning, space checking and also replacement) to be a typical practice. Spark plugs would become dirty end a fairly short period of time (~15,000 miles) indigenous the lead in gasoline and also the carbon from incomplete combustion. In addition, the facility electrode would certainly burn away, boosting the plug gap. Failure to store spark plugs clean would result in performance and beginning problems. Spark plug maintain was a major matter.

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But, together engine control an innovation progressed, spark plugs remained cleaner for much longer periods that time, reducing maintenance tasks and extending business life. Everyone was amazed as soon as the instead of cycle came to be 30,000 miles or 60,000 miles, or the unthinkable 100,000 miles! And, when the plugs were eventually replaced, the plugs were often clean however with burned electrodes. The melted electrodes would result in excessively broad plug gaps that would cause performance problems.


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

Not just are the organization intervals because that replacement different, but not all hemi engines use the exact same spark plug. That’s an essential point since some are a standard thread design and some are tapered subject (see Figure 1). This two different designs room not interchangeable. Installing, or rather trying to install, the wrong style spark plug can damages the spark plug and, fairly possibly, the thread in the cylinder head.

The 5.7L spark plug is a traditional architecture with directly threads. It’s additionally nickel-plated. The 6.4L SRT engine plug has actually tapered threads and has a platinum resistor design. The resistance values range from 3,500 come 20,000 ohms when checked with at the very least a 1,000-volt tester. Do not usage an ohmmeter to examine 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 space 16 come change, no eight. Also, it should be listed that all hemi V8 engines use coil-on-plug ignition systems. Every except the 2004-2005 engines, that is. Let’s look at that device in some an ext detail as replacing spark plugs on this design is different than the procedure because that coil-on-plug.

The early 5.7L hemi V8 engines space equipped through eight separate and independent ignition coils. The one-piece coil bolts straight to the cylinder head cover. It attaches the second output terminal directly to the spark plug utilizing a rubber boots seal. Every coil has a second output terminal. The 2nd terminal associate a conventional spark plug cable to a spark plug on the contrary cylinder bank. A different primary electric connector is offered for every coil.

The spark plug cables that connect the coil come the spark plug on opposing cylinder financial institution are placed and routed in a one-of-a-kind plastic loom to save the cables separated. The impend is clipped to the entry manifold. To avoid a mismatch that cables, a corresponding spark plug/coil number is presented on every spark plug cable. These numbers are situated on the optimal of the entry manifold to the appropriate of the throttle body.

Now, let’s review the steps to replace the spark plugs top top the 2004-2005 5.7L hem engine … eight of the 16 spark plugs are situated under an ignition coil, those coils will need to be removed.

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

Check the spark plug space on the brand-new plug (see Figure 2). Be sure the gap meets spec. Special treatment should it is in taken when installing the brand-new spark plugs right into the cylinder head spark plug wells. Begin the spark plug threading right into the cylinder head by hand to prevent cross threading. To assist installation, to the right a piece of rubber water tap to the new plug. This plugs room a torque-critical design, so execute not exceed 15 ft.-lbs. The torque as soon as tightening the plugs.

Install the spark plug cables. Use dielectric grease within the boots to assist installation. To avoid ignition crossfire, the spark plug cables must be placed in the routing impend in the initial positions. Download the ignition coils to complete the installation.

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

Install the new spark plugs. Begin the spark plug threading right into the cylinder head by hand to stop cross threading. To assist installation, fit a piece of rubber water tap to the brand-new plug. Tighten the spark plugs come the suitable torque:

5.7L engine – 18.5 to 22 ft.-lbs.

6.4L engine – 7.5 come 15 ft.-lbs. (do no exceed 15 ft.-lbs.)

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

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Note: always tighten spark plugs come the stated torque; excessive or poor torque will cause damage come the cylinder head or spark plug.