'88 5.0L OMC coil question

[JKEP44]

Hello, I have an '88 5.0 L Cobra and am having some dificulty with it dying suddenly. I learned through searches that there is a resistor in line from the Alt to the pos side of the coil. I checked my voltage at the pos side of coil with key in "on" position and only had 4.5Vdc. I then removed the wires on the pos side and found a full 11vdc with key in "on". Both ground wires from the neg side of the coil have good continuity with low resistance. The resistance from the PURP/RED (coil end) to the PURP (Alternator end) is .010ohms. Does this mean my coil is bad or the resistor is bad or what? Is there a way to test the coil through resistance? Any help would be greatly appreciated.

 

[searay3]

Re: '88 5.0L OMC coil question

No really effective way to check a coil. Cheap part to replace + peace of mind. The 4.5 volts on the pos side sounds low. I believe it should be around 9v with the key in the 'run' position. The OMC guys I'm sure will clarify. Be sure and clean and tighten the connections. As was stated before in other posts...looking at the connections is not good enough. Remove, clean, replace the connections. It's a place to start....good luck.

 

[Boatin Bob]

Re: '88 5.0L OMC coil question

Your points were probably closed when you checked and you were charging the coil. When checking voltage on the resistor wire you should make sure the points are open and you should see somewhere around 9 volts or so.

 

[JKEP44]

Re: '88 5.0L OMC coil question

So is this what the purpose of the resistor is, to keep the 12V produced down to 9volts? If so and I have a bad one does anyone know how many ohms resistance that resistor is so I can wire one in. The book says that if it is bad you need to replace the entire harness.

 

[KaGee]

Re: '88 5.0L OMC coil question

The purpose of the resistor wire is to reduce the voltage to make the points last longer. If the wire were bad... you could buy a Pertronix Flamethrower coil that requires no resistor wire.<br /><br />But before you go swapping parts you need to determine if you have spark when your engine quits.

 

[JKEP44]

Re: '88 5.0L OMC coil question

So this pertronix coil needs to receive a full twelve volts? Will it damage the points in some way? My engine dies immediately when it goes from the start circuit to run circuit so I know that I am loosing spark. I am recieving too many volts (11vdc) to the coil in on with the wires disconnected. When I connect the wires the votage at the post drops to 4.5vdc. this leads me to believe that a shorted resistor burnt something in my coil. I am going to check to see if my points are open or closed today and go from there.

 

[rbezdon]

Re: '88 5.0L OMC coil question

KEP, you are not on the right track at all. You are getting the correct voltages with the wires disconnected. Search this site for the troubleshooting proceedure posted several times. I know Don S and I have posted troubleshooting proceedures and tips several times as well as others. You are on the track of replacing parts and spending money and not getting to the root cause. With your discussion I can tell you do not yet understand how the whole ignition system works. Unless you are rich and have a lot of time do not make the change you are considering. Yes the Pertronix coil takes the 12v directly but not with out replacing the whole ignition system or you'll just burn up points. My suggestion, get some one to help you who understands ignition systems or read all the old postings until you do.