"BMW Z3 - How to Replace Spark Plugs"

Ron Stultz

Summary: easy enough do-it-yourself if you have tools.

Background:

BMW Z3: 1997, 2.8L, 63,000 miles.

Bought new.

Valve cover leaking oil so while at it, did spark plugs.

At 63,000 miles and almost 20 years old, never plug replace.

Tools needed:

Spark plug socket.

Ratchet.

2 short extensions.

Tube of antiseize compound, not required.

10 mm socket.

10mm wrench.

Small flat blade screw driver.

Pliers.

Set of plugs. I used BMW Bosch, "hot" plugs.

Remove cosmetic dust cover

With plenty of light and engine cold, pry off the 4 plastic covers on the cosmetic dust cover.

Now use ratchet to remove nuts and bolts holding plastic dust cover in place.

Now using pliers, remove hose connected to dust cover.

Remove oil filler cap.

Lift dust covers off engine. Note: there are 4 small rubber gaskets on the edge of the cover that are held only by pressure into slots in the edge of the cover. When you remove cover, make sure you get these 4 gaskets and they do not fall into engine or are stuck to edge of actual valve cover.

Replace oil filler cap.

Remove coils:

There is one coil assembly per plug.

To remove coils, first unhook the coil cable.

To remove cable, use small flat blade to pry up the metal clamp where the coil cable connects to the coil assembly.

The metal clamp simply moves up to allow connector to be pulled out.

Now use 10mm socket and ratchet to remove 2 bolts holding first coil to valve cover.

With bolts removed, simply slowly lift and twist coil outward.

As shown above, the coil assembly has a very long shaft on it with rubber where it fits over the spark plug.

The first and last coils have a ground strap under one of the 2 coil bolts. Make sure to put it back when you reinstall coil.

Remove and replace plug:

With coil assembly removed, use spark plug socket, ratchet and extensions to loose plug and remove.

In my case, the first plug was in very tight. When I confront "tight" I try for a while and then back away.

Do not want to strip threads on plug or break off plug in head.

With first spark plug removed, take a new plug and apply antiseize compound to threads. Not required but helps next time plugs are removed.

Insert plug into socket and with extensions only, lower plug into hole until plug is at bottom.

With new plug in head, hand tighten plug. Do not use ratchet. Hand thread.

Once plug is hand tight, use ratchet to draw it snug. Do not know exact torque defined for plugs but nice and snug will do.

Now take a break, walk away. You have done one. When you come back, make sure plug is snug into head.

With first plug replaced, replace coil assembly and tighten back down and connect coil cable.

Move to next plug and repeat process defined above.

When you come to plug 6, going to probably have to use 10mm wrench to get coil assembly out as little room under wiring panel hooked to firewall and loosening it does not help.

With coil out, probably going to have to use 2 small length extensions to get spark plug socket down into hole and around old plug. Once on plug, attach second extension and then your ratchet.

Going to have to use similar approach when putting new plug into head. One extension with plug lowered into hole and then second extension and after hand tighten, ratchet.

On last plug, do not forget ground strap that does under one of the 2 coil assembly bolts.

Now time to break and walk away. An hour.

When you return, look over everything. All coils bolted down with 1 and 6 having ground strap attached??

All coil cables connected to coil assembly and all metal connector clamps pushed back down and in place?

Nothing in valve cover that does not belong there?? No pieces of anything???

Put cosmetics dust cover back on:

Once you are sure all is as it should be, lift up dust cover and check edges for those 4 small rubber gaskets.

Now slowly lower the larger of the 2 cover over the engine and making sure the rubber around the coil wiring cable fits into the groove in the cover, lower the cover into place.

Use 10mm socket and ratchet to attach both covers.

Replace 4 small plastic covers over bolts.

Put hose back on cover.

Put oil filter cap back on. Note here, there is a rubber ring around the oil fill hole in the dust cover and make sure it is in place.

Once again, break and walk away.

With good light, check over everything. Nothing in there that does not belong??

Ok, start the engine. Might run rough for couple seconds as you have had cylinders open to air while replacing plugs but then it should run smooth.