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Old 06-26-2003, 11:47 AM
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EricSilver EricSilver is offline
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Join Date: Mar 2000
Location: Fairfax, VA
Posts: 1,249
Do spark plug wires overheat??

1989 260E, 183,000 miles
Weather: has been hot 95+ with engine coolant temperature at 80-85 during all types of driving.

In the past two days, my car failed to immediately start after sitting for about 15 20 minutes after normal city driving. It would crank but not start. This only happened during the daytime, when the outside temperature was highest.

In the first incident, I was coming back from the grocery store after about 20 minutes. After three or four attempts the car would crank strongly, but not start. I raised the hood and saw that the long plastic case that contains the plug wires had detached from the block and was dangling over the side. The wires had come mostly out, but the case was still snapped together at the end, towards the back of the block. I laid the whole thing on the block, and tried starting the car. It fired right up, and behaved normally thereafter. When I got home, I reseated the wires and reattached the plastic case to the block.

The second incident occurred this morning. Again, it was about 90 degrees outside and as I was rolling into a parking space, the engine quit. (Actually, the timing was perfect; it stopped at the very moment I rolled into the space.) On two restart attempts, the engine would fire weakly in the 200-300 rpm range and then stop. After looking under the hood, the plug wires were in their proper place. All I did was tap the wire case to be sure it was not loose. Tried starting the car and it fired up with a little struggle, and I pulled into an indoor parking garage to cool the car off, where the engine conveniently quit, again, just as I rolled into a space.

I checked under the hood again, and on a whim, pulled the distributor wire (where it connects to the ignition coil) and then reseated it. Restarted the car and it fired up very strongly, and idled steadily.

Based on that, I dont think anything is wrong with the plug wires themselves (after all, how does a wire fail?). Is it possible for old wires (mine appear to be original) to overheat and stop conducting??

I don't think there is a problem with the ignition coil, OVP, or pump relay, which are all still fairly new. The alternator is fine. I dont think it is vapor lock either. The only thing that seems to make sense is a heat + electric problem involving the connections between the plug wires and the ignition coil and/or distributor and/or spark plugs. I assume there is dirt, oil, corrosion or some other impedance where they connect to the spark plug wires. Perhaps there is similar corrosion in the distributor itself.

Because I am at work right now there is not a great deal I can do. I am really paranoid because when I drive home the outside temperature will be over 100 degrees. If I make it there without incident, my plan is to clean every electrical contact between the ignition coil and spark plugs. If anyone can offer some additional advice and insight, Id really appreciate it.
2001 E430 4matic
122,xxx miles
Black/Charcoal Interior

Gone but not Forgotten:
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black
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