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1998 S320LWB
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659 Posts
Discussion Starter #1
Does it make sense to replace as a maintenence item the ignition spark plug wire set at 150K miles. Car running fine but I would expect a failure would take out a coil pack. Also, is Bosch as OEM supplier from Autohaus be ok or need I go with original MB part. What do most of you do?
 

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1997 S600 (sold)
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4,660 Posts
Are you talking about your 1998 W140? You don't have old-school spark plug wires on this car. For older generation cars with distributor ignition with thick, high voltage spark plug wires, 10 years is probably a good interval for the wires.

The low voltage wire harness to the coils in your 1998 W140 won't likely ever need replacement.

Brett
 

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1995 S500 coupe, 1990 Mazda Miata
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694 Posts
At that mileage I believe I would consider replacing. Check for stiffness in the wires and the correct test is to check resistance. The Bosch set is fine but a couple of wires are too long. The OEM set up consists of separate wire and ends; the wire must be assembled. The good part is you can tailor it perfectly, the bad being the wire is only as good as your crimps.
 

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1997 S600 (sold)
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4,660 Posts
At that mileage I believe I would consider replacing. Check for stiffness in the wires and the correct test is to check resistance. The Bosch set is fine but a couple of wires are too long. The OEM set up consists of separate wire and ends; the wire must be assembled. The good part is you can tailor it perfectly, the bad being the wire is only as good as your crimps.
We were typing at the same time. I notice you have an LH-SFI 1995 model with the usual distributor ignition.

Brett
 

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1998 S320LWB
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659 Posts
Discussion Starter #6
Zeroing in on the answer

We were typing at the same time. I notice you have an LH-SFI 1995 model with the usual distributor ignition.

Brett
Brett,
You were right the first time. Being a 1998 104 engine, I have no distributor. However, the wires going from the 3 coils to the spark plugs are not "low voltage" which you stated in your first response.. Instead these wires from the coils to the spark plugs are high voltage with a specified resistor. I was just wondering if for $100 they were worth changing out proactively.
 

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1997 S600 (sold)
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4,660 Posts
Ah, I stand corrected. Thank you. I forgot the last generation M104 used the HFM engine management system with a waste spark arrangement. I would say, yes, replace high voltage wires every 10 years as good preventative maintenance.

Brett
 

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1997 E320, 1997 S320
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2,946 Posts
i wouldn't replace them if there is no problem. i don't have that many miles on the s320, but my e320 has 260k miles with original wires and no problem. mb doesn't have a replacement interval for the wires. just change the plugs (copper/non-resistor) and 3 connectors every 40k miles.
 

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1998 S320LWB
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659 Posts
Discussion Starter #9
Spark Plug Connector Questions

i wouldn't replace them if there is no problem. i don't have that many miles on the s320, but my e320 has 260k miles with original wires and no problem. mb doesn't have a replacement interval for the wires. just change the plugs (copper/non-resistor) and 3 connectors every 40k miles.
Two questions: Referring to attached picture of Bosch Spark Plug Wire Set. I assume the 3 connectors you are referring to changing is directly below each coil and I assume the 3 connectors simply screw out of the bottom of each coil. But why would these resistor elements wear any differently than the other 3 (those on the end of the wire).
 

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1997 E320, 1997 S320
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the 3 connectors (coil to plug) have no wires, they are just resistor encased connector and are heat trapped under the hot coil. these connectors are one of the most common cause of misfire in m104. that's why mb mechanics always change them when replacing the plugs. and use only copper/non-resistor plugs, bosch f8dc4 is oem and cheap. the 3 connectors are pretty cheap also.
 
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