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Jim Grant Tech Tips Jim Grant Tech Tips
A collection of helpful articles based on reader submissions
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Below is a collection of Jim Grant's Tech Tips sorted by Vehicle Make. These Tech Tips were answers to questions submitted to Jim by users over the course of many years.
If you have any questions, please feel free to email us.



Lincoln - Mercury
  Jim Grant's Tech Tips

'92 Ford F150, Misrouted Plug Wires

Q: I have a '92 5.0L F150 that has run great for years. In the last year or two, however, it's steadily declining. I've taken it into the dealer for a tune-up, wires, etc. Most recently, it was discovered that spark plug wires 7 and 8 were routed next to each other -- a big no- no according to some Ford TSB's on the subject. According to the TSB's, plug 8 will fire when plug 7 fires. It was also discovered that the #8 cylinder only holds 30 lbs of compression. The dealer essentially stated that the misrouting of plug wires caused a burned valve scenario to occur. Does this make sense to you and could you explain it to me?

- Mike

A: How does one spark plug wire cause another spark plug wire to fire? Believe it or not the condition you're referring to is a rule of electricity and the principle of that rule is used to make the spark for the ignition at the ignition coil. Whenever electrical current travels through a conductor/wire a magnetic field is formed around that wire. If you place another wire next to the first, nothing really happens until the electricity/current stops moving thorough the first wire. When current stops moving the magnetic field collapses. When invisible lines (called magnetic flux) of the magnetic field collapse they will cut through the second wire. Here's where it gets really cool. As the lines of flux collapse and cut through the second wire, it just happens to create electricity in that wire. This is called mutual induction. Mutual induction is applied in many aspects of or lives, cars, computers, home appliances are just a few items that rely on this rule of electricity. Now, I know anyone that has looked under the hood of a vehicle would say how can this happen? After all nearly all the plug wires run side by side, so there should be more problems. That is true, but for the problem to occur and affect engine operation you need to add a few more pieces to the puzzle. Ford did that by having two cylinder firing events close to each other. To make power with an engine, air and fuel are mixed, compressed and spark is added at a very precise time. It just so happens in some Ford engines the next event getting ready to happen is in the next cylinder. If the spark plug wires are routed side by side the first cylinder receiving spark just happens to induce a voltage that is great enough to cause a spark at the plug in the next cylinder. The problem is, it is at the wrong time! This causes all kinds of disorder. This condition can cause spark knock, engine misfire, false computer codes and driveability problems. If driven under these conditions for a prolonged time it is possible for engine damage to occur. You would know your engine is not running right and would find it very difficult to ignore. Proper plug wire routing is important. If you ever want to create real havoc just run a critical computer wire along side a spark plug wire.

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