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Introduction
Applicable to H4D and H4Bt engines (M281 E10 and M281 E09)
It is advisable to do this operation on a cold engine.
Recommendations :
OEM replacement: every 60,000km/4 years.
Warning: will vary downwards depending on a large number of factors!
Some fuel additives contaminate the spark plugs (see wiki). Replacement may be necessary after as little as 10,000km!
See the Wiki for more information.
What you need
Featured Document
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Unscrew the 6 screws by hand or with a T50 socket.
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Lift and set aside the engine hood.
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Disconnect and put aside the oil vapor duct.
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Disconnect the ignition coils' connector.
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Unscrew each 8mm bolt of the 3 ignition coils.
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Gently extract the ignition coils.
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Unscrew and extract the spark plugs using a 14mm spark plug socket.
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Typical color of MMT contamination: (Methylcyclopentadienyl)manganese tricarbonyl, an organo-metallic fuel additive that can, according to ACEA reports and my own experience, render spark plugs unusable sometimes in less than 10,000km.
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Check and adjust the gap using shim sets. Maximum gaps for 95RON E10: 0.70mm for the H4BT, 0.80mm for the H4D.
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E85: Reducing the gaps may be beneficial or even necessary, depending on the spark plug type and engine. See the wiki for more details. You should primarily base your decision on idle quality and the linearity of engine response; any hitches or hesitations may indicate an improper gap.
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Optional: Draw a red line with a marker to mark the position of the open side of the spark plug if indexing is desired later. You can also draw a black line to mark the closed side and number the spark plugs.
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Torque the new spark plug by hand using a 14mm spark plug socket at 24 N · m, or until it reaches the stop.
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Optional: If specific indexing is desired (e.g., open side facing the intake), note the current spark plug position, unscrew it, and add calibrated washers accordingly to create rotational retard.
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Tighten the spark plug to the mandatory torque of 24 Nm (RTA) or 23 Nm (Bosch).
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Reposition the ignition coils onto the spark plugs until they are fully seated.
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Tighten the single 8mm screw on each coil to a torque of 10 Nm.
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Reconnect the ignition coil connectors.
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Ask FixBot
Congratulations! You replaced your spark plugs/ignition coils!
The idle is still not satisfactory? Then it might be time to clean the MAP sensor, injector tips, and throttle body :)
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