1989 560SEL

Mercedes wraps the 4 plug wires in a bundle between the distributor cap and the top of the valve cover. Won't this increase the chance of cross firing? Especially on adjacent cylinders that fire in order like 1&2.

I've worked on '60s Fords and the shop manual was always very specific about plug wire routing to avoid cross firing. There were specific instructions on how to layout the cables on top of the distributor cap to keep them perpendicular to each other as well as instructions to keep the cables seperated from each other.

Why is it the MB doesn't seem to be concerned about cross-firing? At least not on the 560 engine.
~Dave

Probably the most significant reason is that MB wires are copper centered instead of the TVRS carbon impregnated string that domestic cars use.

If the ceramic resistors at the ends of the wire go defective they will cross fire but there is little likelyhood any other time as the wires in effect have zero resistance.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

I hooked up an inductive timing light to each plug wire. I noticed that on cylinders 2, 3 and 4 the light seemed to have an erratic flash. All cylinders on the left hand side had steady beats as well as cylinder #1. Does this test mean anything? My test is not very scientific, the timing light could be too sensitive or I could be imagining things. I have new Beru plug wires installed. I've been investigating why the idle on my 89 560SEL is a little rough. I haven't rulled out a vacuum leak or fuel problem. BTW, the timing at idle appears to be 12 degrees BTDC. Shouldn't it be more like 4 degrees at idle. Is there a better way to measure the timing advance on this car? The timing chain was replaced recently as well.

I've ordered a new coil to see if that helps. I don't really want to solve the problem by swapping out parts but since it looked like the original coil and I plan on keeping the car for another 100K miles I don't mind in this case.

Thanks
~Dave

Two years ago I had Beru wires on my 300SE, lasted 3000mls. Before there where Bosch on it, lasted 100K mls. Now back to Bosch, after 20K mls still working fine. The Bosch wires are thicker less flexible, and last much longer.

I'm not trying to adjust the timing, just measure it.