How to change BMW M54 and M52U spark plugs

Here is how to change the BMW M54 and M52U spark plugs used in the Z3, Z4, E36, E39, E46, 325i, 330i, 525i and other straight-six-engined models.

The BMW M54 engine and its M52U sibling are known for a great noise, rapid performance and reliability if looked after properly. One way to keep things working efficiently, besides regular oil changes, is to change the spark plugs.

Spark plugs can last somewhere between 30,000 and 100,000 miles, which is not much help. It is best to check them manually to see their condition while possibly revealing other issues in the process.

Purchasing spark plugs from BMW is likely to be the most expensive option. NGK is the original equipment manufacturer (OEM) so you can just buy the correct model from Amazon, Ebay or any other reputable automotive supplier.

Having taken the spark plugs out of my BMW Z4 E85 3.0-litre, I can see they are the NGK BKR6EQUP. Not the cheapest available, but come highly recommended. I have heard less positive things about the equivalent Bosch FGR7DQP with regard to quality control.

Tools & equipment

• Flat-head screwdriver / Trim removal tool
• 12″ or longer wrench or socket with 10mm hex bit
• 5/8″ thin-wall spark plug socket
• 6 spark plugs (one per cylinder)

The instructions

1) Remove the engine covers

Before we can do anything, we need to remove the two plastic covers on top of the engine. Using a flat-head screwdriver, trim removal tool or something else flat, gently remove the four screw covers (two per cover).

Beneath the covers are four 10mm bolts, which you can undo with a wrench or socket and the appropriate 10mm hex bit. Be careful not to drop them into the engine bay and put aside somewhere safe for refitting later.

2) Remove the ignition coil electrical plugs

Next, remove the six electrical connectors that plug into the ignition coils. Rotate the plastic catches up to partially release all six connectors then pull them out.

If extremely stuck, you may need to carefully wriggle the connector or pry open a gap using a flat-head screwdriver or something else strong and flat. Removing the plastic catch by separating the two lugs it uses to rotate can work too.

Keep the ignition plugs assigned to the same ignition coil they are removed from. This should be done for you due to pre-existing cable guides in the engine bay, but it is worth mentioning just in case.

3) Pull out the ignition coils

With the ignition plugs disconnected, we can now remove the ignition coils. If suction is keeping you from removing them, remove the oil cap (remember to refit as soon as possible). Wriggling side to side with upward force should eventually free each ignition coil.

Put safely to one side and consider giving them a gentle clean. A degreaser, brake cleaner, electrical connector cleaner or IPA work well. Just remember to dry and remove any residue before reinsertion later.

4) Take out the spark plugs

Sitting beneath the six ignition coils are the six spark plugs (most likely NGK, as previously mentioned). To remove them, we need to attach a 5/8″ thin-wall spark plug socket to a wrench with an extension around 12 inches in length.

Before that though, consider using a vacuum cleaner, some compressed air or both to remove any debris from the ignition coil as, once the spark plugs are out, it will be able to drop into the engine.

Rotate anti-clockwise (righty tighty, lefty loosey) to undo the spark plug. If access is inhibited, you may need to remove a coil insulator using ring-snap pliers or similar.

Assuming the spark plugs were fitted properly in the first place, they should come loose without too much force. Brands such as NGK do not need thread lube as they are pre-coated. However, a mechanic may have used some and over-tightened.

5) Fit the new spark plugs

Modern-day spark plugs such as the four-prong NGK Platinum I am using for the BMW Z4 E85 3.0-litre do not need to be manually gapped as they come ready to go from the factory.

Remove and fit each spark plug, one by one, so they are protected in the box until needed. Gently tighten to ensure the threads are aligned. Stop if you feel too much resistance and try again until movement is easier.

How tight do the spark plugs need to be? 23Nm +/- 3Nm (17ft/lb +/- 2.2lb/ft, to be precise. If you do not have a torque wrench, finger tight then an extra 1/2 to 2/3 of rotation (180 to 240 degrees).

Under-tightening and over-tightening have their respective issues so take your time and ensure a firm, consistent level of tightening across all six spark plugs.

6) Re-install the rest

With all six spark plugs in, re-insert all parts and components from beforehand. Only this time, in reverse order. Ensure your ignition coils are clean, dry and debris-free before reinserting to their maximum depth.

Then reconnect the six electrical ignition connectors and fold down the plastic clips to lock them in place. Now re-attach the plastic covers and then the four plastic bolt covers.

Feel free to give said covers a gentle degrease and dry for a smarter engine bay though this is entirely optional.

7) Test the spark plugs

Now it is time to start your M54 or M52U-engined car. Allow the oil and fuel to prime then twist to start the car. Assuming all went well, the engine should spring to life and your spark plugs are good for tens of thousands of miles.