4.5 D-Jet: W108 vs. w116
 

need some help here for i've become thoroughly confused regarding spark plug application; specifically resistor vs. non resistor plugs. i've searched the archives but every post i've found regarding plugs for a 4.5 D-Jet car refers to the W108/W109 chassis; i've got an early '73 W116 with the 4.5 with D-jet.

here's the source of my confusion; the original owner's manual specifies non resistor plugs. (i'm currently running with NGK BP5ES plugs with no issues from a driveability standpoint.) i've got wires with 5K Ohm spark plug connectors and the ignition system is bone stock except for the green condenser wire in the dizzy is severed to protect the points.

i just checked both the online and paper catalogs for NGK and Bosch and both of them recommend resistor plugs for my car. i know Bosch has stopped making nonresistor plugs so i expected that, but i was suprised to see that NGK recommended a resistor plug (BPR5ES.) i also looked up plugs for a '73 W108/W109 with the 4.5 for comparison's sake and NGK recommended a NON resistor plug.

so my question is, is the ignition system in a '73 W108 4.5 that different than essentially the same engine in a '73 W116 4.5? are there updates and parts supercessions that i don't know about?

any help would be greatly appreciated and i thank all who took the time to read my rather long winded post.

The difference? The w116's m117 had a different oil filter housing setup. Hence the different engine number. Otherwise, all w116's with the EARLY m117 (D-Jet, 52/52-series cams) should follow requirements for the w108/109.

I'm under the impression that you do not mix resistor plugs with resistor wires, altho resistance core wires (VS resistance in the connector) are a different animal.

The resistance reduces the RF/EMF interference emitted by the plug wires and adding the additional resistance of resistor plugs is overkill and can reduce the spark energy at the plug.


Michael

tomguy,

thanks for the response and clearing that issue up.

250 coupe,

i completely agree with you; mercedes has pretty much always put the resistance in the secondary in the spark plug connector and used non-resistor plugs. what further confuses me is the fact that Bosch, the OE supplier for plugs for a lot of benzes, has stopped making non-resistor plugs and now recommends them for cars that originally came with non-resistors. they make no mention of removing resistance in the secondary to compensate. for me, i'm mainly trying to figure out the engineering logic behind this.

Of course Beru still makes plain Copper core plugs w/o resistors.

BUT the resistance in the NEW Bosch plugs is VERY low...won't cause any problem in a "D" jet engine. IF you follow the service schedule they are to be replaced every 10,000 miles any way.

ONE of the biggest differences on the W116 engine was the ignition system..

Much higher output than the older 280SE/SEL 4.5 systems

Not on the earliest models that still had an identical setup, from what I've seen on junkyard cars. In '76 they went breakerless, though.

that's what i was starting to think, that the W116 4.5's ignition was understressed in the stock configuration and thus could handle a bit of added resistance in the secondary.

tomguy,

during the 4.5s run in the W116, at some point they switched distributor caps from the "push in" type to the type with the male threaded studs. is this indicative of an entirely new/different ignition system than the ones on the W108/W109 and early W116 4.5s? (i can't remember off the top of my head if this switch occurred at the same time they switched from D-Jet to K-Jet...

thanks guys for taking the time to respond...much appreciated

There was 3 Versions OF "breaker" style transistor systems... the 1973-76 cars used the version 3...the 280se 4.5 used version 2.

IF you are happy with your NGK BP5ES, stick with them. My 107 loves the NGK BP6ES. Some newer counter catalogs list only resistor plugs...not sure if it is because they are no problem when mixed with resistor wires, or simply to reduce inventories. My newer cars of other makes all use resistor plugs and resistor wires, but then they have ignition systems that make a spark you could weld with.

230/8

is it then safe to assume that each newer version was/is more capable of delivering more spark than the prior versions?

my litany of questions isn't to solve any driveability issues with my own car but i'm just purely curious as to why MBZ kept changing things. i'm assuming that with each version there must be some engineering benefit to correct whatever shortcomings the engineers at the time felt prior versions had...

Version 1 failure rate was out of sight...possibly 90%.

Version 2 was probably less than 10% & the version 3 was around 1% or less.

Of course they went Breakerless in 1976.

Every step was an improvement in technology.

thanks to MB Doc and Tomguy for responding to my posts. much appreciated!