Before the days of emission controls, lead-free gasoline and also clean burn engines, spark plug maintain (cleaning, void checking and replacement) to be a typical practice. Spark plugs would become dirty over a fairly short duration of time (~15,000 miles) from the command in gasoline and also the carbon native incomplete combustion. In addition, the center electrode would certainly burn away, boosting the plug gap. Fail to keep spark plugs clean would bring about performance and beginning problems. Spark plug maintain was a severe matter.

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But, together engine control an innovation progressed, spark plugs stayed cleaner for longer periods that time, reducing maintenance tasks and extending business life. Everyone was amazed once the instead of cycle ended up being 30,000 miles or 60,000 miles, or the unthinkable 100,000 miles! And, when the plugs were eventually replaced, the plugs were frequently clean but with shed electrodes. The melted electrodes would an outcome in excessively broad plug gaps that would cause performance problems.


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

Not just are the company intervals because that replacement different, but not all hemi engines usage the very same spark plug. That’s crucial point since some room a conventional thread design and some are tapered subject (see Figure 1). These two various designs are not interchangeable. Installing, or rather trying to install, the wrong layout spark plug can damage the spark plug and, fairly possibly, the subject in the cylinder head.

The 5.7L spark plug is a traditional design with right threads. It’s likewise nickel-plated. The 6.4L SRT engine plug has tapered threads and has a platinum resistor design. The resistance values variety from 3,500 to 20,000 ohms as soon as checked through at least a 1,000-volt tester. Perform not usage an ohmmeter to examine spark plug resistance as an inaccurate analysis will result.


There space two spark plugs every cylinder in a hemi V8 engine. So, once the plugs need replacing, there space 16 to change, no eight. Also, it need to be listed that all hemi V8 engines usage coil-on-plug ignition systems. All except the 2004-2005 engines, the is. Let’s look at that mechanism in some more detail together replacing spark plugs on this design is various than the procedure for coil-on-plug.

The early on 5.7L hemi V8 engines room equipped with eight separate and also independent ignition coils. The one-piece coil bolts directly to the cylinder head cover. That attaches the an additional output terminal straight to the spark plug utilizing a rubber boot seal. Every coil has a 2nd output terminal. The 2nd terminal connects a typical spark plug cable come a spark plug on the opposite cylinder bank. A separate primary electric connector is provided for each coil.

The spark plug cables that attach the coil to the spark plug on the contrary cylinder financial institution are placed and routed in a unique plastic loom to save the cables separated. The loom is clipped to the input manifold. To prevent a mismatch of cables, a matching spark plug/coil number is displayed on every spark plug cable. These numbers are situated on the optimal of the intake manifold come the best of the accelerator body.

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

Before removing or disconnecting any type of spark plug cables, note the initial position of the cables. Eliminate the cables one in ~ a time. Spray compressed air into the cylinder head opening for each plug. This will avoid dirt indigenous entering the burning chamber. Remove the spark plug.

Check the spark plug void on the new plug (see Figure 2). Be certain the space meets spec. Special treatment should be taken as soon as installing the new spark plugs into the cylinder head spark plug wells. Start the spark plug threading right into the cylinder head by hand to avoid cross threading. To help installation, fit a piece of rubber hose to the brand-new plug. This plugs are a torque-critical design, so perform not exceed 15 ft.-lbs. The torque once tightening the plugs.

Install the spark plug cables. Use dielectric grease inside the boots to aid installation. To protect against ignition crossfire, the spark plug cables must be put in the routing loom in the initial positions. Download the ignition coils to complete the installation.

For all hemi V8 engines constructed after 2005, spark plug replacement is a bit much more straightforward. Together mentioned, these engines are equipped v coil-on-plug ignition systems. First, remove the engine cover. Then, disconnect the ignition coil wire harness connector. Eliminate the two ignition coil bolts, then, v a slight rocking motion, remove the coil (the rubber boots space integral through the coil).

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

5.7L engine – 18.5 come 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 same manner for the other seven cylinders. Install the engine cover.

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