Spark Visible To The Naked Eye

[Mikebear79]

I took the 560SEL for a little drive tonight and when I pulled it back into the garage, I let it sit running so I could pop the hood and listen closely to the engine for any strange noises. All of the lights were off and it was pretty much pitch black in the garage, so to my amazement, as I was leaning closely over the driver's front fender, I noticed that I could see a faint pulsing of spark in the line that crosses directly behind the lid of the power steering pump. There was also a streaking pulse that was not as consistent that traveled on the same line between the cap/rotor and the power steering pump. Is this normal or do I need to change the wires soon? Again, totally dark out and just detecting a faint sparking pulse on those areas. Thanks - Mike

[optimusprime]

Is the wire going to the coil ? And yes to the question , it is time to change all the ht leads . Or for now just pick up the one thats shorting out on the power steering lid. Put some tape over the king wire to isolate it from the power steering pump lid .

[97 SL320]

Mostly you are seeing corona, this is an effect of high voltage on a conductor. Even with good insulation it is possible to see this.

A test for failing wires is to lightly mist them with water and look for large sparks / engine miss fire.

Wet or not, don't handle the wires as if they are actually leaking, you will get a shock.

[Diseasel300]

Time for new wires. The wires are insulated to prevent cross sparking or grounding. Seeing sparking means the insulation has cracks or a rubbed break in it. The HV system on a cap/rotor ignition system is not high enough to cause corona if the insulation is intact. Solid-state ignition with a distributor-less coil pack is a different story, but this engine is not that type of system.

[97 SL320]

So, you are saying that at a 0.035" plug gap, a cap - rotor point type / point / electronic ignition system won't make corona but DIS using the same gap will?

[ejboyd5]

Mikebear79 stumbled upon a diagnostic method employed by generations of automobile enthusiasts to locate ignition malfunctions: Put the car in a dark place and look for errant sparking. Start the overhaul by replacing the high tension wires. Regardless of the type of ignition employed, visible sparking or even a corona is not desirable.

[Diseasel300]

Originally Posted by 97 SL320

So, you are saying that at a 0.035" plug gap, a cap - rotor point type / point / electronic ignition system won't make corona but DIS using the same gap will?

Corona is a very undesirable thing in anything electrical. The systems are purposely designed to AVOID corona.

Cap/rotor style ignition systems typically operate at a lower voltage and higher current than DIS systems to. If corona were a common occurrence on them, they'd routinely flash over inside the distributor cover, not through the HT wires. Eventually as they age, they do begin to flash over due to carbon tracking and contamination inside the distributor cap.

DIS systems operate at a MUCH higher voltage and a higher current than rotary distributor systems do. Modern coil-on-plug systems can easily break 100KV and having a "corona ring" around the porcelain insulator on the spark plug is not uncommon when the plugs and insulator boots get some age on them. That is still not "corona" in the sense of the word though.

Corona depends on atmospheric conditions to form, typically requiring very dry air to ionize the air and form a corona ball. If the conductor forming the corona ball is close enough to a grounded object, the corona will become an arc and ground through the object before it is ever visible to the naked eye.

Bottom line, corona or not, if you're seeing sparks coming from HT leads, they're done. Their entire purpose is to insulate the conductor, not dissipate the spark energy as coronal discharges.

[Ivanerrol]

There's a flat disc behind the rotor on the distributor. This has a rubber seal on it.
These break down and spark escapes (grounds) through to the block.

A smallish parts that seems to be rather expensive but should be replaced when a distributor cap is also replaced.

I've seen some cars where this disc has never been changed. Owners have been frustrated by misfires, have changed leads, plugs, dizzy cap and rotor but never changed the disc - and the disc ended up being the source of the misfire.