After driving 2 blocks I knew something was wrong with the engine, and when I stopped and checked under the hood I discovered that 4 of the 8 spark plug leads were there but disconnected.

This was the first time the car was driven after someone had given it a 'tune up'. I always wondered if it could have been dangerous if I hadn't stopped and checked this myself just before I got on the highway? I was never able to ask the person who did the tune-up. Thank goodness I knew a little bit and reconnected the leads before I drove any further.

My question is this "how dangerous would this have been to my vehicle and/or myself" if I had not caught it so quickly? Thanks very much for your opinion.

  • 1
    Who does a "tune up" without actually starting the engine and making sure it's running smoothly afterwards?? Jun 1, 2013 at 3:17
  • I wasn't going to mention this but it was my ex-husband and he just disappeared the next day. I've always questions whether or not he did it on purpose, as he had always serviced our vehicles and this never happened before. This was in 1993. Thanks for your responses
    – wisteria
    Jun 6, 2013 at 22:46

2 Answers 2


The two biggest risks I can think of are fire, destroying the catalytic convertor and possible exploding a muffler. The arcing of the plug wire could ignite the underhood insulation. The extra unburned fuel could ruin the convertor, the fuel could collect in the muffler and ignite rupturing the muffler. All these are worse case scenarios if the distance is a short as you say the damage would be minimal.

  • 2
    As far as the damage to the cat, if you can inspect it easily, do so. I drove one car 2+ hours with only 3 of 4 cylinders firing and did no damage. However, I had another car suddenly lose the power transistor (resulting in NO cylinders firing, but fuel still injecting). Just during the coast down to stop and 3 subsequent attempts to start I put enough fuel in the cat to make the car smell like it was on fire and melt the guts of the cat. We didn't realize the cat was melted until we put the car on the dyno and chunks of catalyst shot out the exhaust... May 31, 2013 at 12:31

The 4 spark plug were not firing so the fuel pumped in those piston can flow out through the exhaust and in worst could catch fire. since the 4 piston were not firing so the rotation could go out of balance and start shaking you engine.

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