How could a carwash cause Jonathan's Porsche to sputter?

Dear Car Talk

Dear Car Talk | Apr 01, 2010

Dear Tom and Ray:

I bought a '72 Porsche 914 a few weeks ago. It was running great for about 10 days. Then I took it through a carwash. When it came out, it ran terribly. It was underpowered, and sputtered whenever I hit the gas. Hoping to clear up the problem, I took it on a long trip (100+ miles), which brought its performance back to normal. Can you explain what happened? And can you tell me how I can prevent it from happening again?

-- Jonathan

TOM: Sure. Hand-wash it.

RAY: What happened was that you got something wet, and then you dried it out.

TOM: Right. That "something" is some part of the secondary ignition system.

RAY: Electricity is supposed to travel from the coil to the distributor, and then through the spark-plug wires to the spark plugs.

TOM: If the insulation on one of those parts has been compromised, and moisture diverts the electricity from its intended destination, one or more of your spark plugs won't fire.

RAY: And that'll make the car sputter and seemed underpowered, because it IS underpowered. It's running on three (or fewer) cylinders.

TOM: Eventually, this problem will plague you in the rain, too, Jonathan. So you'd be wise to fix it now.

RAY: It should be easy to diagnose. Take a spray bottle and fill it with water. Then, on a dry night, open up the engine compartment, start the engine and begin spraying one suspect at a time.

TOM: First, spray the coil tower. That's where the coil wire plugs in. If you see sparks jumping in that area, the coil's no good, and it probably has a hairline crack in the tower.

RAY: If you don't see any sparks around the coil, then move on to the spark-plug wires. Spray them one at a time, starting at the spark plugs and moving toward the distributor. If you don't get any sparking around the wires, then spray the distributor itself.

TOM: Or if you want to save time, just skip the diagnosis and replace everything. Chances are, on a car of this age, you need all that stuff anyway. Good luck, Jonathan.

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