I have been told the 351 (5.8 liter) V8 engine in my 1989 F350 truck may suffer from "cross firing" on number 7 and 8 cylinders. To correct this potential problem I have to be carful how the spark plug leads are positioned. The trouble is I can't find out how they should be positioned or how serious this problem really is. Can anyone spread some light on the topic?

 

Most spark plug wires have to contend with 30,000-40,000 volts of electricity. If the silicone wrapping is not thick enough, or is cracked, the voltage will arc to the nearest ground. Try to keep the wires away from each other and away from the metal engine components. If this doesn't work, try some better plug wires. I use Taylor Spiro-Pro wires on my truck and Mustang. They're priced a little more than "factory replacements" but work great.

 

Crossfire is caused by "induced" voltage. When current is carried by a plug wire a magnetic field forms and collapses around the wire during the duration of spark. An adjacent plug wire running in close parallel will generate a current enough to cause a spark at the plug (much like a coil). Many a youngster has taped together his plug wires to improve his underhood appearance only to find his engine ran REALLY bad afterwords. The fix is to separate ignition wires as much as possible and if necessary to cross wires, do so at 90 degress. HTH