Trying everything I can think of to avoid replacing a fuel distributor. I have a dead cylinder and a black, carbon covered spark plug. causing rough idle. I will be testing the wires, plug, and dist cap over the weekend. I cracked the line at the fuel distributor and at the injector and did get fuel with the the motor running. I also put my stethoscope on the injector and I could hear a clicking from the injector that sounded like all the others.

Can I assume that if the injector is "rattling" that it is getting and injecting fuel? Does this imply that my problem is with ignition?

Thanks.

J. Boggs

Would help to know what car.

Fuel distributor suggests some variety of K-Jetronic.

Try running the engine with no spark plug in the dead cylinder. You should smell raw fuel.

It could be an ignition problem, oil leaking into that cylinder problem or no compression in that cylinder problem.

If you have an inductive timing light you can check ignition very quickly.

Sixto
91 300SE
87 300SDL
83 300SD

Good idea on the smell.

My timing light has one of those clips that surrounds the cable. Would I just have to put it around the spark plug wire to the suspect cylinder. Sounds easy enough.

Thanks.

J. Boggs

If the spark plug's not firing, the timing light won't fire either.

Of course the wire could be bad between the clip and the plug but that's a lot easier to trace.

Knowing that it's an M117 if the bad cylinder is the one by the firewall on the passenger side (#4?), my guess is a bad valve stem seal or guide.

Sixto
91 300SE
87 300SDL
83 300SD

I put my timing light on it, and it sparks ok but every 8-9 flashes or so, it doesn't spark. I moved it to 3 or 4 other wires and they were all constant, no miss. I pulled the distributor cap and there were no obvious cracks or deposits although it did have some blackened areas around the perimeter.

Question: Should the contact points be smooth, shiny metal? Mine are rough.

Probably time to replace it I'm thinking. Maybe that'l solve the problem.

Thanks.

J. Boggs

I'm not familiar with the distributor in an 86 560SL but I doubt it has contact points as such. Maybe you mean the contacts in the distributor cap and the contact on the rotor? They're not contact points since they're not supposed to touch. Over time the heat of the arc jumping across will cause the contacts to deform or something like that.

Hope fully that's all you need.

I hate to see you throw parts at it though.

Sixto
91 300SE
87 300SDL
83 300SD

I reversed the 3 an 4 spark wires (at both ends) to see if it was a wire, but the symptom stayed with the #4 cylinder-so I guess the wires are oK. Timing light still flashes 6-7 times then off then back on 6-7 times . repeats but not exactly the same every time. The other cylinders I checked are all right. Does it matter that the plug is carbon covered as to whether the timing light would flash or not?

Thanks.

J. Boggs

It could be that the carbon build-up is causing the plug to misfire. If the plug doesn't fire, the timing light won't light.

Have you checked the gap of that plug? Have you tried a new plug in that cylinder?

What's the compression in that cylinder? I'll bet a penny it's higher than the others.

Sixto
91 300SE
87 300SDL
83 300SD

Nearly new plug. But I'll clean it up and test the compression tomorrow.

Points contacts are supposed to be smooth and clean. Pitted ones mean replacement.

Check each plug wire from the inside contact of the distributor cap to the plug connector end. Move each wire as you test. You might find one wire that is broken.

Keep us posted,

Haasman

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RE: What noise should a fuel injector make?

Well, it sort of "sings". 8 of them sort of sing in concert.

KE injectors don't make noise because they're always spraying. EFI injectors click but not as loudly as Diesel injectors.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD