420SEL- spark plugs, cylinder order, distributor - MBWorld.org Forums

S-Class (W126) 1979-1991: 300 SE, 300 SEL, 380 SE, 380 SEL, 420 SEL, 500 SEL, 560 SEL, 360 SEC, 500 SEC, 580 SEC, 300 SD TURBODIESEL, 300 SDL TURBO, 350 SD TURBO, 350 SDL TURBO

420SEL- spark plugs, cylinder order, distributor

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Old 03-08-2009, 03:06 PM   #1
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420SEL- spark plugs, cylinder order, distributor

Can anyone help me with these questions?

  • What is the order of cylinders in my 1986-420SEL? Is #1 the one on the passenger side at the front of the car, does it go until #4 at that side and then start with #5 on the front of the driverís side?
  • The manual says that it takes Bosch W8DC plugs; now it has Bosch W9DC; are they ok?
  • Which ones are the hotter ones?
  • What are the gaps for either kind? The dealer told me different gaps than I found on the web, 0.035 vs. 0.032 while now they are gapped 0.050.
  • How do I take the distributor cap off? The wires will not come off.

Thanks for any help.
erhard is offline   Reply With Quote
Old 03-12-2009, 02:37 AM   #2
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Firing Order is 1-5-4-8-6-3-7-2
Plugs W8DC or Equ with Gap to 0.032 / 0.8mm
You'll have to wiggle the wires off of the Dist-Cap by the rubber boots. Try twisting left to right. If replacing with new & they're really stuck simply split the rubber boot with a razor blade & that should permit you to remove easily......
The Dist-Cap is removed via 3-Screws once you get the wires off...
Be certain you have their positions marked properly before removal so you put them back in the proper position(s)...... or you'll misfire!!!
Also, if removing the Dist-Rotor be careful, there is a Latch-Lock you will need to relieve before it comes off. Don't pull with force; take a pick-hook & catch the tab, pry up slightly & it will come off! You can apply a little dielectric grease to the wire boots when installing the new ones to prevent the problem you have now & prevent moisture.
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Old 03-28-2009, 08:20 PM   #3
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While your doing all that you should lubricate the throttle linkage joints, just another tip, thats what i did when i did the same job on my 87 420sel
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Old 04-02-2009, 01:54 PM   #4
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does any one else have problems replaceing the rear spark plugs or is just me?
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Old 04-02-2009, 03:10 PM   #5
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You need a universal attached to the socket to get to the back left plug.
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1991, 420sel, bev, changing, cylinder, firing, linkage, order, plug, plugs, remove, removing, spark, throttle, w126, wire

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