Spark plugs


Cost: $20


Time: 30min

Buy it now


A spark plug is an important part of the ignition system as it produces the spark that ignites the petrol/air mixture in the engine's cylinder. The spark plug can have a dramatic effect on the performance of the engine, it must therefore be checked on a regular basis to maintain the performance of the engine. Below are some hints on the correct replacement procedure for spark plugs.


  • Spark plug socket or spark plug tool
  • Rachet, extensions and u-joints if needed
  • New spark plugs

1- Identify which spark plug lead fits which cylinder. A suggestion is to attach numbered tags to the respective leads if no other identification is available.
2- Pull the connectors off the plugs. Do not pull on the cable.
3- Ensure that the spark plug tool is securely fitted before trying to remove the plug.
4- Check the gap on the new plugs, see below.
5- Fit the new plugs with a little piece of plastic tube and tighten to finger tight.
6- Using a spark plug tool, tighten the plugs between and of a turn from finger tight. Refer to the owner's manual for torque specifications.
7- Fit the plug connectors in the correct firing sequence and ensure they are securely attached to the plugs.
8- Start the engine. If it does not run smoothly, repeat step 1 to 7 and check that the plugs have not been damaged during tightening. Check ignition leads and replace if necessary, also check for cracked insulators, air gap etc.


Spark plugs appearance

Check this website that explains eveything about how to read spark plugs with pictures.


Bosch platinum +4

Can you install Bosh platinum +4 in your car? Hummmm, I don't know, basically everyone has a different opinion if this is good or bad for the engine, and if this gives more power or a smoother idle...

If you feel like wasting some money (these are not cheap), you can try them... and send me an e-mail if it is working.


Part numbers

525i (89-90) M20 - 535i
Regular Bosch W8LCR Gap: 0.7-0.8 mm (0.028-0.032 in)
(On the 535i, set them slightly larger to 0.86-0.91mm (0.034-0.036in to help improve the idle.)
Platinum Bosh W8LPR (alternate choice)

525i (91 on) M50 - 530i - 540i
Bosch F7 LDCR Non adjustable

Thanks to Joseph Phan

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