Rod Spohn

Over the weekend my car started running bad on the freeway. A code (I think 0305) misfire on cylinder #5 came up. I cleared it and it seemed OK. Then on the way to work the same thing happened. I replaced the wires about a year ago or less. So I was thinking the coil!! But if a coil goes bad wouldn't it affect 2 cylinders since they each feed 2? How would I test a coil? Or does anyone have an idea of what is wrong?

Sorry - this is a '96 S320 - it has no mods. It has 165K other than a few minor problems has always run great.

AH1W-COBRA

the coil fires two plugs but they are both the same cylinder,it could absolutely be a coil.im simply basing this reply on memory.i cant imagine why a single coil would be expected to handle multiple firing orders.and you can measure the primary/secondary windings,i dont have the specs though.you could also swap with another coil on the same side and see if the miss follows the suspected coil.

Rod Spohn

This is a straight six and only has 3 coils each has a conector that goes rite on 1 plug and a plug wire that goes to the second. But swapping one out to be sure thats the problem is go good idea . Thank you

09385
Bosch
Spark Plug Wire Set; OE Type; 3 Wires Only
For models with engine serial number through 016468. The 3 short connectors shown no longer come in the Bosch wire set, please add (3)0001593642 connectors to any order of this wire set 1 set per car. Limited Lifetime Warranty.
Sorry photo didn't want to copy but you can get the idea- 3 wires - 3 connectors

bicylindrico

Check your plugs. Combustion gases will pass up around the ceramic and contaminate the boot. This will be seen as a dark ring around the base of the ceramic. This will lead to carbon tracking up the ceramic portion of the plug and cause a misfire. The carbon tracking will look like very fine black lines on the spark plug that can be felt with your fingernail. Very common on the M104 for some reason.

Also check for brittle insulation in the engine harness. Pull off the cover for the plugs/coils and reinstall the intake. Wiggle the suspect coil supply wiring and check for misfiring. Hope this helps.

AH1W-COBRA

i should have looked at the modle year since it was posted.im thinking V configueration.

Rod Spohn

Well before I read your post I pulled the plug from #5 and whipped it off before reinstalling. Then I also swapped coils around & cleared the code. Drove it around and had not code come up. After reading your post I remembered how the base of the plug was dark that’s why I whipped it off. Didn't notice carbon tracking but then didn't wasn't looking for it. The car seems fine except for a slight hesitation on acceleration from a light. I checked my records and found I last changed the plugs 42k ago. I’ll change them this weekend and see if that helps. I would have thought the platinum plug would last longer than that. At least that’s what I was told.
Anyway thanks for the great reply

bicylindrico

No problem. It would be wise to apply dielectric grease to the plug boots when you replace the plugs. It can be purchased at any auto parts store. This can help to prevent problems in the future. We always installed the Bosch Copper plugs in that particular engine.

Rod Spohn

I just wanted to follow up and thank you again for the advice. Put the new plugs in and put the electrial lube spray on all of the boots as I went along putting in the new plugs. Everything is back to normal & running great. No more Platnum plugs for me.