OMC ignition coil question...external resistor

[ereid74]

Have a 1983 starcraft with a 3.8l omc (gm) and it had a ford coil on it that was supposed to be used with an external resistor..does the 3.8l use an external resistor? i couldn't find one but its tight back there! thank you.

 

[Howard Sterndrive]

Re: OMC ignition coil question...external resistor

yes, the 3.8 has a resistance wire... the purple/red wire feeding the coil is 2 ohms. it gets quite warm too.

 

[ereid74]

Re: OMC ignition coil question...external resistor

is that the wire going from the distributor to the negative side of the coil? Thank you!

 

[bruceb58]

Re: OMC ignition coil question...external resistor

No, it is one that goes to the positive side.

 

[ereid74]

Re: OMC ignition coil question...external resistor

Alight thats what i thought, but wasnt sure. Does it mean my resistor is bad if i have 12.3v coming out of that wire? or will i have 0 if the resistor is bad? I thought i was only supposed to have ~9v? Thanks yet again!

 

[ereid74]

Re: OMC ignition coil question...external resistor

ALSO my key isn't killing the engine anymore? something else must be powering the coil? and my oil stays on when the battery is hooked up, but goes off once engine is started?...bad ignition switch?! Thanks

 

[bruceb58]

Re: OMC ignition coil question...external resistor

Could be how you wired up your alternator.

With the ignition on(engine off) and the points closed, you will see a voltage drop at the coil(should read around 9V at the coil). With the points open, you will see battery voltage at the coil.

 

[ereid74]

Re: OMC ignition coil question...external resistor

alright so i had the boat running for about 20 min today..ran great! i shut it down and threw the battery charger on it because it was drained from cranking it over so much..the oil light stayed on, but i didn't see it taking that many volts...I came back about an hour later..engine was cool but the coil gave me 2nd degree burns! i pulled the positive off the battery and its currently cooling down? It was reading about 12.4 volts at the coil and im not sure if the points were opened or closed..im about to check it with the points open and see if it drops down to 9....BTW i haven't touched ANY wiring..the alternator has been wired the same since i bought the boat..im looking to change ignition switches? ill brb to report on volts with points open...btw i don't have a dwell meter and just set the points by eye..it breaks contact and the engine runs fine? should i still dwell it?

 

[bruceb58]

Re: OMC ignition coil question...external resistor

You have it backwards. With the points closed it should be 9 and points open 12.

If the coil was really hot, then the points were probably closed since no current will flow through the coil with the points open. If the voltage with the points closed is 12V, then someone bypassed the ballast resistor which is why your coil is so hot.

btw i don't have a dwell meter and just set the points by eye..it breaks contact and the engine runs fine? should i still dwell it?

Absolutely! You always want to use a dwell meter to set your points. Some people will say gap is enough but they are wrong. Once you set your dwell, set your timing since dwell affects timing.

 

[ereid74]

Re: OMC ignition coil question...external resistor

hmm everything seems to be great but the coil is still reading at about 14v when the engine is idling? shouldnt it only be 12? am i going to be burning up coils?

 

[bruceb58]

Re: OMC ignition coil question...external resistor

hmm everything seems to be great but the coil is still reading at about 14v when the engine is idling? shouldnt it only be 12? am i going to be burning up coils?

Yes you could damage your coil.

I will ask this question again...what is the voltage with the engine not running and the points closed? You cam simulate the points closed by jumping the negative side of the coil to ground if you don't want to open the cap.

 

[ereid74]

Re: OMC ignition coil question...external resistor

about 4.5v

 

[bruceb58]

Re: OMC ignition coil question...external resistor

That sounds very low. If it drops that much then you do have a resistor in there.

 

[ereid74]

Re: OMC ignition coil question...external resistor

and it goes up to 11.9 with the points open...battery was just charged though and is ~13.1v

 

[bruceb58]

Re: OMC ignition coil question...external resistor

and it goes up to 11.9 with the points open...battery was just charged though and is ~13.1v

Impossible for a charged battery to be 13.1V unless you measured the battery voltage right after pulling the charger off. Max it can be is 12.6V. Where do you have your meter's ground when making these measurements?

In any case, it sounds like you have a resistor in there. Is that your only question?

 

[ereid74]

Re: OMC ignition coil question...external resistor

it was right off of the charge and when measuring the batter it was just positive to negative posts on the battery...and I know the coil has an external resistor...The coil has 5 wires going to it...2 lighter gauge which, one to the negative and one to the positive which run while the engine is running correct? there are 2 heavier gauge wires (one to the negative and positive) which are used when cranking the engine over right?the fifth wire is just the trigger wire from the distributor...so i guess what my question is; what should the voltage be when measuring the positive of the coil and just an engine ground, while the engine is running? I have an external resistor so I thought it should only be about 9v at the coil with the engine running? But im getting ~14v

 

[bruceb58]

Re: OMC ignition coil question...external resistor

That could possibly depend on your meter and that is not going to be a very good measurement because the voltage is varying. Depending on your meter, it could be an average of the voltage while the points open and close or it could be more of a peak measurement which could explain why you see 14V.

There should be two wires on your positive side of your coil. One is from the resistor wire and the other is from the starter solenoid to bypass the resistor wire while cranking.
There should be two wires on the negative side with one going to the points in the distributor and one to the tachometer.

Not sure what your fifth wire is being used for but it could be for an electric choke if you have one. Would be nice if you could locate a service manula for your engine that showed a schematic.

What you saw measuring 13.1V was a surface charge on your battery. True battery voltage should be measured 20 minutes after taking off a charger or after a small load is applied to the battery.

 

[Lyle29464]

Re: OMC ignition coil question...external resistor

5 th wire may go to the interrupter switch

 

[bruceb58]

Re: OMC ignition coil question...external resistor

5 th wire may go to the interrupter switch

Yes...of course!

 

[ereid74]

Re: OMC ignition coil question...external resistor

Does this mean I have a bad resistor? Or do you hunk a peak of 14 v is normal at idle? Maybe ill see if the voltage spikes with gainage of rpms? Any other way to test it? 4v with points closed should mean my resistor is working correct?