Old Spark Plug Wires the Cause of a 470 Mercruiser Engine to lose RPMs.

Magstar Marine Spark Plug Wire Set for 4-Cylinder - Mercruiser 470, 485, 488, and 3.7L OMC 2.5L and 3.0LRecently, I was running my 1983 17 foot Formula One off of Playland Amusement Park in Rye, New York for an early morning water ski session. In Long Island Sound, finding flat water can be a challenge at times. This particular morning the condition were ideal , but my 470 Mercruiser had another idea. While skiing at 4300 rpms, the engine started to break up and misfire. To add insult to injury, the skier I was pulling at the time, wiped out face first into a Jellyfish with bites all over his face.

At first, with the ethanol in the fuel and the problem of dealing with phase separation being very common in the northeast, I thought my issue was a fuel related. I check the filter in the carburetor, replace the fuel filter attached to the fuel pump and added a 10 Micron Water Separator Fuel filter as an additional fuel filter. After all this work, I still had the engine breaking up at higher RPM with a load on the engine.

Since the points, condenser, ignition coil and plugs were all change with very little hours on them, I did not think the issue was ignition related. The one item that was not changed over in years (possible 10 years) was the Spark Plug Wires. In my case the #1 Cylinder spark Plug wire was malfunctioning, resulting in the #1 Cylinder to misfire. Once I replaced the Spark Plug wires, my 470 Mercruiser operated normally.

Also I found that the Volt Meter was charging at 13.5 to almost 14 volts. Prior to the change in Spark Plug wires, the volt meter was always below 13 volts. Since the charging system in the 470 uses a Stator and not an Alternator, the reduction of resistance in the old wire, resulted in the higher reading in the Volts.

An ideal set for the Mercruiser 470 is the Magstar Marine Spark Plug Wire Set for 4-Cylinder – which fits the Mercruiser 470, 485, 488, and 3.7L; OMC 2.5L and 3.0L. They claim to be designed Exclusively For Marine Engines and that Magstar is the only high performance marine wire set that practically eliminates radio interference with onboard electronics. They have Stainless steel spark plug terminals provide a positive corrosion-proof connection. They also have pure silicone boots provide maximum heat protection. They are guaranteed for as long as you own your boat.

Magstar Marine Spark Plug Wire Set for 4-Cylinder - Mercruiser 470, 485, 488, and 3.7L OMC 2.5L and 3.0LIf you have a Mercruiser 470 and need spark plug wires, I found them on Amazon.com.


If I replaced these wires every 2 to 4 years, then I would not of had this issue and lost one perfect morning of water skiing. The lesson learned in my case is that some of the simplest bits of maintenance that can be performed are the most important in keeping “This Old Boat” operational.

This entry was posted in Bertram, Bertram 28, Bertram 30, Bertram 31, Bertram 33, Boating, Chris Craft, Crusaders, Ethanol, Marine, Mercruiser, Mercruiser 470, This Old Boat, Thunderbird Formula. Bookmark the permalink.

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