Troubleshooting why a Mercruiser 470 Inboard/Outboard does not start

After a long winter layup for my 1983 17 foot Formula One with a Mercruiser 470 I/O, the engine would not turn over on the first start of the season. The engine was winterized properly and was running well at the time of winterization. An engine that is turning over, but is not starting has 1 or 2 possible issues. It is either a Fuel related issue or an Ignition related issue. For the non mechanic, to troubleshoot this is quite easy. I found this the inline spark plug tester with a light below on for about 7 bucks, however you can also go to you local auto parts supply store and purchase for about $8 to $12 dollars.

To use the tester is easy, you plug one end on top of the spark plug and the other end into the spark plug wire. When you try to start the engine, if you have power going to the spark plug, the inline light will light up, thus indicating that the problem is a fuel related issue. Obviously, if the light does not light up, then what you have is an ignition related issue. In my case it was an ignition related issue, as the light did not light up on start up.

So, the first thing I checked after that is if I had power going into the coil. With a mutimeter that I had bought at Radio Shack for $20 a few years ago, I confirmed that there was power going to the coil. What I did was I took off the coil the hot wire, then I turned the ignition key to the on position and tested the hot wire, which showed voltage of a little less than 8 volts. This normal as that wire is attached to a resistor, which keep the voltage to the coil in the high 7 volts range. So now I know the problem is either the ignition coil, condenser or points.

The first point of attack should be the points. FIRST THING IS MAKE SURE YOU TURN THE IGNITION TO THE OFF POSITION AND THE BATTERY SWITCH IS IN THE OFF POSITION OR DISCONNECT THE BATTERY. If power is going to the points, you could get a shock, so make sure you take this precaution. Now, I took the distributor cap off, then the rotor, exposing the points. With my fingers, I opened up the points and with some sand paper, I scratched up thoroughly both contacts on the Points. Then I put the Rotor and Cap back on. Then I turned my Battery switch to the On position. (if you disconnect the battery, you must make sure you reconnect the battery and turn all battery switches on). Now, with one crank, the Mercruiser 470 fired up and ran like a charm.

To help troubleshoot this issue, you need an inline spark plug tester with a light. To fix this issue, all you really need is a Phillips head screwdriver to get the distributor cap off and a little piece of sand paper. The test light is very cheap and a great tool to have at your disposal when owning “This Old Boat”.

This entry was posted in Bertram, Boating, Crusaders, Ethanol, Marine, Mercruiser, Mercruiser 470, This Old Boat, Thunderbird Formula. Bookmark the permalink.

4 Responses to Troubleshooting why a Mercruiser 470 Inboard/Outboard does not start

  1. Ron Blight says:

    I have good spark coming from the coil to the distributor on my 1986 190 Mercruiser. There is no spark going to the plugs. I then installed a new cap, rotor, points and condenser. There is still no spark to the plugs. Any ideas?

  2. Perry Degener says:

    The 6 volt systems are tricky. I have a 1957 6 volt Chris Craft. I changed the coil, points, and condenser. Still no spark. Any ideas?

  3. Administrator says:

    If you still are not getting a spark after changing everything, then check your spark plug wires.

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