4.3 no spark voltage at coil drops from 12.6 to 2 volts or less while cranking

[Fun Times]

Re: 4.3 no spark voltage at coil drops from 12.6 to 2 volts or less while cranking

The - of the coil was connected to the distributor base. When I hit the remote starter, I got a very weak spark, almost invisible, but it was not enough to fire up the engine. but only .5V at the - of the coil.

Hi there, The - on the coil does not work as a typical ground like you would see on a 12 volt battery system.

Since you are grounding out the - side of the coil to an engine block ground, that would be a/the reason you have no spark like you are describing. There should only be two gray wires going to the - side of the coil. One to the tachometer, the other to the ignition control module.

As mentioned by dingdongs, disconnect the gray wire going to the tachometer to see if you regain spark once you disconnect the wire between the - side of the coil and the distributor base.

Good luck.

 

[achris]

Re: 4.3 no spark voltage at coil drops from 12.6 to 2 volts or less while cranking

When hooking up for a 'test stand' run, just connect the battery positive as you have, the battery negative to engine block, and your remote starter switch. To turn the engine 'ON' connect a jumper wire from the battery positive to the coil +... That's all you need to do, then just press the 'GO' button on the remote. Nothing needs be on the coil- except the grey wires currently on it. But I would also disconnect the tacho feed grey wire and the wire from the shift interrupt switch (on the coil -), so you should only have one grey wire on the coil-, the one that goes to the ignition module.

Chris...

 

[mbasura]

Re: 4.3 no spark voltage at coil drops from 12.6 to 2 volts or less while cranking

Thanks for the help on this gentlemen I think we may be getting to the bottom of it. I think the culprit is the black wire that is currently connecting the - post on the coil to the distributor base. This may be wired wrong see below.

I have disconnected the tach and the switch interrupt with the same result, no spark at coil. What I have never done is tried to start without the black wire from the - post connected to the base of the coil. I have always left that in place as I thought it was needed to ground the coil.

This black wire may be the issue, it seems painfully obvious now, when it is disconnected I have 12V at + coil, when connected it drops to 2V or less. What does this wire do? I cannot say that I have tried to start the engine without this black wire connected to the distributor base.

Keep in mind that I have a OMC/Mercruiser hybrid (maybe bastard is a better description). Could this be an issue? I have an OMC engine (as achris pointed out) and have been using a Mercruiser manual and hence a Mercruiser wiring diagram. Could this be making me wire the engine wrong? Are they that different?

I can't get to the boat today but hopefully someone can shed some light:
1) does an 1986 OMC 4.3 boat have an ECM module? I have crawled over every inch of the engine and have never seen it.
2) What is the black wire from the base of the distributor to - on coil do? Will the boat run without it being connected?

 

[achris]

Re: 4.3 no spark voltage at coil drops from 12.6 to 2 volts or less while cranking

Answering the questions...
1) Post photos of the distributor area and we can see exactly what you have.
2) Then there should not be a black wire from the distributor body to the coil-. There should be a black wire from the distributor base to the engine block. But there should be a wire from the points to the coil-. Are you sure this errant black wire is connected to the base of the distributor, and not passing into the distributor to connect to the points?

Chris....

 

[mbasura]

Re: 4.3 no spark voltage at coil drops from 12.6 to 2 volts or less while cranking

Here are the photos of the distributor. Clarification: the black wire from - post on coil threads through distributor and goes to points and condenser. Without black wire attached to - post, I was reading zero volts at pos coil and (needless to say) no spark. Once black wire attached from distributor to - post, coil would heat up noticeably even without attempting to start. Lively sparking at neg post while attaching black wire. This must be where the issue lies, but I cannot explain. Note coil is new and I have not bolted down yet.








The final two photos are were taken trying to get the engine to start in the "test stand" condition, that is with everything bypassed except starter, coil and distributor. Even with the pos coil directly wired to the battery, only reading .4 V at the pos on coil. 12V measured at neg post. Does this make any sense?

 

[dingdongs]

Re: 4.3 no spark voltage at coil drops from 12.6 to 2 volts or less while cranking

have you changed the condenser as it may be not working correctly

 

[achris]

Re: 4.3 no spark voltage at coil drops from 12.6 to 2 volts or less while cranking

I noticed a purple and a tan on the coil +... Should only be the purple. That coil, does it have anything written on it? Like "Use with external resistor"?

What I would do is remove all the wires from the coil +, hook a wire straight from the Bat+ to the coil +... Remove all wires except the one running to the points and condenser from the coil-... With the points open, does the coil still get hot? If not, see if you get spark. If the coil still gets hot with the points open, you have a short in the wire from the coil- to the points or faulty points or condenser.

Chris......

 

[mbasura]

Re: 4.3 no spark voltage at coil drops from 12.6 to 2 volts or less while cranking

have you changed the condenser as it may be not working correctly

I have never replaced the condenser, but it did pass the condenser test. I am fairly convinced the issue is somewhere in the cap/rotor/distributer and have a Pertronix Ignitor on the way.

Thanks. I will report back.

Matt

 

[mbasura]

Re: 4.3 no spark voltage at coil drops from 12.6 to 2 volts or less while cranking

I noticed a purple and a tan on the coil +... Should only be the purple. That coil, does it have anything written on it? Like "Use with external resistor"?

What I would do is remove all the wires from the coil +, hook a wire straight from the Bat+ to the coil +... Remove all wires except the one running to the points and condenser from the coil-... With the points open, does the coil still get hot? If not, see if you get spark. If the coil still gets hot with the points open, you have a short in the wire from the coil- to the points or faulty points or condenser.

Chris......

Yes coil is marked "use with external resistor."

I followed the instructions above and removed all wires except for black wire to points/condenser and ran a jumper from pos on the battery to pos on the coil. The coil did not heat up noticeably prior to attempting to start. I measured .4V and hit the starter and saw a very weak, almost imperceptible spark. After about 5 to 10 seconds of cranking the coil was almost too hot to touch.

I was able to replace the wire from the neg post on the coil to the points (but not the condenser) and the voltage at the measured at the coil jumped to 2.4V, still not enough, but maybe an indication there are issues.

As stated I am going to replace the points/condenser with a pertronix ignitor unit and will revert.

 

[Bt Doctur]

Re: 4.3 no spark voltage at coil drops from 12.6 to 2 volts or less while cranking

You dont measure the - post of a points system, only the +side for 12V.
Remove the - wires from the coil. jumper 12v to the + side. use a jumper from the - side and scratch it to a good ground, this should produce spark. if not, coil is bad.
To test points, hold open with a matchbook and using a jumper or screwdriver short across the contacts, this should produce spark.
If not points are not making contact or condensor is bad.