What causes burned distributor cap terminals?

[shogunther]

I am having a spark problem with my car. It has intermittent spark. I took off the cap and the terminals are black(looks like carbon or burned). Can this be causing the intermittent spark? Can I just sand off the carbon and reinstall the cap? What causes this discoloration? Thanks for looking!

[nynor]

dirt or oil on the terminals can cause this. i think that worn terminals/rotor can cause this as well. the spark between the terminals and the rotor takes a small amount of material off every time, i think due to ionization. over time, the gap between the two points becomes greater and greater, requiring more energy make the jump and taking more material with it. this affects all kinds of things, like timing and spark energy and can/will make your car run crappy.

[LockDr816]

Originally Posted by shogunther

I am having a spark problem with my car. It has intermittent spark. I took off the cap and the terminals are black(looks like carbon or burned). Can this be causing the intermittent spark? Can I just sand off the carbon and reinstall the cap? What causes this discoloration? Thanks for looking!

Yes, it can cause intermittent spark. If it is an aftermarket cap, there may be small, hairline fractures in the cap, causing cross detonation. Additionally, a weak secondary signal coming from the coil will cause carbonation of the terminals and the plugs. What's the year, make, and model?

[shogunther]

It is a 1985 1/2 944. The cap is about 6 months old.

[John_AZ]

Originally Posted by shogunther

I am having a spark problem with my car. It has intermittent spark. I took off the cap and the terminals are black(looks like carbon or burned). Can this be causing the intermittent spark? Can I just sand off the carbon and reinstall the cap? What causes this discoloration? Thanks for looking!

Do not sand the terminals inside the cap. The gap is critical. I use a Dremmel with a soft wire brush to clean the terminals. Wipe the cap to remove carbon archs inside

It is a Bosch cap, right?

Causes.
What type of plugs are you using? I suggest only the cheapest single tip copper plug that Porsche used for your 1985.5 944.
Wires--how old are the wires?
Rotor-did you change it when you changed the cap. Pelican sells an aftermarket I use for about $7.50.

GL
John_AZ

[shogunther]

John,

Yes it is a Bosch cap. I am using NGK Iridium plugs. New rotor. Im not sure how old the spark plug wires are...they look oem. I just noticed that one of the wires is aftermarket. I am starting to suspect the ignition switch is bad. Will the engine turn over with a bad ignition switch?

[Nottom]

Like platinum, iridium is used to prolong the life of the plug but it also has higher resistance than a traditional copper plug. Higher resistance means higher voltage required to make the spark. The iridiums were designed for modern high-voltage ignition systems that are capable of 100k volts or more.

As someone else mentioned, a set of copper plugs will likely address the issue.

[John_AZ]

Originally Posted by Nottom

Like platinum, iridium is used to prolong the life of the plug but it also has higher resistance than a traditional copper plug. Higher resistance means higher voltage required to make the spark. The iridiums were designed for modern high-voltage ignition systems that are capable of 100k volts or more.

As someone else mentioned, a set of copper plugs will likely address the issue.

++1^^

Ignition switch. I just looked up the price in Pelican parts. Early=$4 Late=$65!

Intermittant spark could be as simple as dirty grounds and cable connections.

Clean every ground. Clean the sensor connections at the back of the firewall.
Remove battery and clean the DME computer connection. Try a different DME relay. Clean the battery connections. Get new wires and cheap single tip copper plugs. The DME is programed for the resistance and length of spark using these plugs.

The ignition switch removal/replacement is not a simple pull out--plug in.

GL
John-AZ

[924Sman]

Could be as simple as the dielectric grease used (if used) that is turning black. Get an eraser and rub off the black stuff then apply new grease.

Dal

[shogunther]

Originally Posted by Nottom

Like platinum, iridium is used to prolong the life of the plug but it also has higher resistance than a traditional copper plug. Higher resistance means higher voltage required to make the spark. The iridiums were designed for modern high-voltage ignition systems that are capable of 100k volts or more.

As someone else mentioned, a set of copper plugs will likely address the issue.

I am getting intermittent spark at the coil wire not the plugs

[shogunther]

I just had the dme tested and it is good. I have also tested the coil. I just removed the ignition switch today and there is a large red wire that is cut under the dash. I also see what looks to be an aftermarket alarm and a small toggle switch. Does anyone have electrical diagrams for under the dash?

Thanks again!

[Nottom]

Originally Posted by shogunther

I am getting intermittent spark at the coil wire not the plugs

Everything I wrote still stands. The coil wire feeds all the spark plugs. If all of your terminals are blackened it could indicate excessive arcing inside the cap due to the higher voltage the plugs are forcing the coil to push out.

The fact that you are seeing an intermittent problem makes it a bit more difficult to diagnose, but you always start with the easiest things first. It's far easier to swap in a set of plain jane NGK V-power plugs to see if that takes care of the issue than it is to start tearing into the wiring harness. Besides, running those iridiums virtually guarantees you further ignition problems in the future.

You haven't told us what sort of driveability issue you're trying to fix here. If there was an issue with the ignition switch you would most likely experience stalling since you would most likely be losing power to the coil, but I'm far from an authority on the details of the engine management wiring.

Again, stick with the simplest things first. I've seen people spend hundreds of dollars not fixing a problem that I took care of with a 7 dollar part.