Mercruiser 888 w/Ford 302 Coil getting hot and stalling at low RPM's

[smarston]

I have a 1973 Marlin that has the combination of the Mercruiser 888 drive and Ford 302 engine. This unit has a mallory distributor on it as well.

I purchased this boat a few months back and had it out in the water a few times and have had difficulty starting it right from the beginning. Once started it would run well. After running a few tests on the engine I replaced the Coil/Cap/Rotor/Points/Condensor/Spark Plug Wires/Spark Plugs. After the upgrades I have had issues. The boat will run and start when cold. Once the boat heats up it runs very rough at low rpm and is very difficult to restart. I have also noticed that the coil is getting extremely hot. This led to another issue with the points, I was having running issues after about an hour or so and would actually have to go back in and readjust the dwell and gap on the points. After resetting this, then the boat would start and run again. The time that this was taking to need adjustment was getting shorter and shorter, to the point it would take about 20 mins to fail.

I decided after talking to a fair number of boating friends that changing to a Pertronix ignitor may fix my situation. I replaced the points with the ignitor, ran a new ignition line as the original was having some voltage issues when on load. None of the wiring seems to be original so colors are not what I have read on this forum for these areas. There was also no ballast resistor or resistance wire on here. I have a coil that has a built in resistor so I didn't think that would cause my issues.

Got the Pertronix installed and everything ran smoothly, but the coil was still getting hot. Took the boat on the water to run it under a bit of a load and the coil was still getting extremely hot and the Pertronix unit failed. I reinstalled the points and fired the engine back up. As I get in to put the boat back on the trailer, the ignition system is getting very hot and it will stall at low rpm, so I end up towing it in with a rope to get it on the trailer.

I have run the tests for spark and everything seems to be ok. I have 2 wires on the negative side of the coil, the shift interrupt and the tach. I have 2 wires on the positive side, the starter 12 volts and the ignition hot wire. I also have the pertronix positive and negative hooked up to the positive and negative, and when I have the points in, I have the negative hooked up to the distributor. I have also noticed with the ignition on, the chassis of the distributor acts as a ground, and the internal plate acts like a ground as well. I do not have a huge amount of experience with points distributors, and am completely stumped.

I have tried to add as much information here as I can, and if there is any advice anyone has for me I would love to hear it. I hope I have not hit on something already covered here, I have been scouring the forum for days and have not been able to find any direction.

 

[jerryjerry05]

Re: Mercruiser 888 w/Ford 302 Coil getting hot and stalling at low RPM's

When you replaced the coil did you replace with a resistor coil? The original setup had a resistor wire.They sometimes fail and get replaced with a new resitor coil.
When supplied with 12V they will overheat and fail and burn the points.
Check the coil for being a resistor coil. Good luck.J

 

[smarston]

Re: Mercruiser 888 w/Ford 302 Coil getting hot and stalling at low RPM's

The coil is one to be used without a resistor, with the internal resistance, and is rated for 1.5 ohms, and tests out just above that

 

[smarston]

Re: Mercruiser 888 w/Ford 302 Coil getting hot and stalling at low RPM's

Well I disconnected the tach, and the start wire(it was not the starter wire just an older wire from the original wiring to give a full 12 volts for startup and then drop back the voltage to the coil with the resistance wire)

So now I have the Pertronix positive and my ignition + on the positive side of the coil and my Pertronix - and the shift interrupt ground on the negative. Still nothing, the starter cranks but it is not even firing at all.

I have 11.9 volts at the coil when the ignition is on measured accross the coil. I have a charger on the system while I am messing with it that is bringing in 12.9 volts, and if I test from the positive terminal on the coil to a ground I get the full 12.9 volts, just get 11.9 when I go accross the coil. I have also noticed that when the ignition is off, the plate inside the distributor that the pertronix unit is installed in also is grounding. I also noticed if I used a meter and test for voltage with the ignition off I am getting a solid ground on the positive side of the coil(meaning if I use a 12 v constant for testing it grounds on the positive side). I also noticed that the coil was heating up with the ignition off. This is probably what is puzzling me the most. When I test accross the coil I am not getting any voltage with the key off, but it is still heating up a drastic amount.

I am a little more than confused now, and any assistance would be greatly appreciated.

 

[MikDee]

Re: Mercruiser 888 w/Ford 302 Coil getting hot and stalling at low RPM's

Why are you using a resistor coil? The pertronix needs a non resistor coil, and you need to remove the resistance wire from the key switch, and run a new full 12volts key switched (run/ on + off ) power source.

 

[cr2k]

Re: Mercruiser 888 w/Ford 302 Coil getting hot and stalling at low RPM's

Is the coil hooked up properly?

I have seen engines run with the coil hooked up backwards and guess what, the coil heats up and breaks down.

Just a thought.

 

[MikDee]

Re: Mercruiser 888 w/Ford 302 Coil getting hot and stalling at low RPM's

One more thing, if the system is a negative ground, as is more common nowadays, you must have a wire coming from the negative side of the coil to the distributor for ground, to complete the circuit. If it were positive ground, the wire would come off the positive side of the coil to the distributor.

 

[smarston]

Re: Mercruiser 888 w/Ford 302 Coil getting hot and stalling at low RPM's

Hmm only one question on the negative coming from the coil to the distributor. Where would that get hooked up? The distributor doesn't have any wiring on it. The points used to have a ground wire run from the coil to the distributor for the points, and now with the pertronix the wires going to the distributor are both for the petronix + and -. There are no other wires on the distributor at all, and the plate the pertronix is on is a solid ground at this point.

 

[smarston]

Re: Mercruiser 888 w/Ford 302 Coil getting hot and stalling at low RPM's

Is the coil hooked up properly?

I have seen engines run with the coil hooked up backwards and guess what, the coil heats up and breaks down.

Just a thought.

The coil is hooked up at this point with ignition 12 v to the positive side of the coil, and the positive and negative for the pertronix unit going to their respective sides. I did have the shift interrupt and tach wire on the ground side as well, but those are removed at present for trouble shooting purposes.

 

[MikDee]

Re: Mercruiser 888 w/Ford 302 Coil getting hot and stalling at low RPM's

Hmm only one question on the negative coming from the coil to the distributor. Where would that get hooked up? The distributor doesn't have any wiring on it. The points used to have a ground wire run from the coil to the distributor for the points, and now with the pertronix the wires going to the distributor are both for the petronix + and -. There are no other wires on the distributor at all, and the plate the pertronix is on is a solid ground at this point.

I see, if you took out the points, then you disconnected the wire from the coil, and the pertronix is automatically grounded. With the Merc manuals online deleted here, I'm trying to go from memory,,, I can't remember if the shift interrupter goes on the positive, or negative, pole of the coil? Either way, it grounds out the ignition momentarily (it seems redundant on the negative side, because your distributor is normally grounded anyway?) Try this, take off the wire, and test it for power (with your igniton on) with your voltmeter (one probe on the wire, & one probe on a good ground) if it shows any power, it belongs on the positive side of the coil! In essence then, it is your REAL orig. igniton powered resistor wire. The interrupter breaks this power when shifting. Let me know what you find?

 

[smarston]

Re: Mercruiser 888 w/Ford 302 Coil getting hot and stalling at low RPM's

I see, if you took out the points, then you disconnected the wire from the coil, and the pertronix is automatically grounded. With the Merc manuals online deleted here, I'm trying to go from memory,,, I can't remember if the shift interrupter goes on the positive, or negative, pole of the coil? Either way, it grounds out the ignition momentarily (it seems redundant on the negative side, because your distributor is normally grounded anyway?) Try this, take off the wire, and test it for power (with your igniton on) with your voltmeter (one probe on the wire, & one probe on a good ground) if it shows any power, it belongs on the positive side of the coil! In essence then, it is your REAL orig. igniton powered resistor wire. The interrupter breaks this power when shifting. Let me know what you find?

The shift interrupt wire did not show any power to it with the ignition circuit on. It was always wired on the negative, and the boat was running this way with the points system on it. Another boating friend of mine here in Lake Havasu has suggested I might have a short elsewhere, and as the wiring for the instrument cluster is 36 years old, I am redoing that this weekend, and tracing for shorts. I will let you know if this finds my issue.

 

[MikDee]

Re: Mercruiser 888 w/Ford 302 Coil getting hot and stalling at low RPM's

No! That is not correct. The distributor provides the ground. If you ground the coil you will get NADA out of it.

Bubba, I think you misunderstood me, Just to elborate, & clarify it further, on a breaker points system, the wire off the negative side of the coil, goes through the distributor, and fastens to the breaker points to energize them, the distributor, is grounded, so it completes the circuit.

 

[topjimmy69]

Re: Mercruiser 888 w/Ford 302 Coil getting hot and stalling at low RPM's

did petronix kit install in prostolite distrib? I tried accel kit 2020 and it wold not install due to the prestolite dist not having a vaccum advance.

 

[WizeOne]

Re: Mercruiser 888 w/Ford 302 Coil getting hot and stalling at low RPM's

....did petronix kit install in prostolite distrib?....

Yes it does but you need to order the proper one and you should start your own post for these questions.

 

[dr_bowtie]

Re: Mercruiser 888 w/Ford 302 Coil getting hot and stalling at low RPM's

I'll try a go at this....

on the original points type the coil was a 6volt coil...the starter wire supplied 12v to the coil during cranking (to compensate for the drop in volts available during cranking) but then is designed to run at 6volts during operation...

the Pertronix can run on either a 6volt or 12volt coil but it depends on what the boat is wired for...

if the resistance wire has been bypassed or replaced with a 12volt direct wire from the ignition source and you are using an original coil it is the 6 volt coil and that would explain the overheating of the coil and burning of the points...

the coils should be stamped or printed on it somewhere the operation voltage...

I personally made this mistake many years ago when I first got into motors thinking a coil is a coil...wrong...