4v at the coil?

[mceachrw]

just picked up a 65 mustang vert and trying to get it running. here are the pertinent specs:
holley 1940 (just rebuilt by me), LOM, pertronix I, SMP FD 471 coil (1.5 ohm primary, 9.6 kohm secondary, 12v - use with external resistor), all inherited from previous owner with unknown history. cap, rotor, wires and plugs are new.

i can get the motor to start but have to hold about 1/3-1/2 throttle to keep it running. dies instantly when letting off the throttle. the coil wire from ign. switch to positive terminal checks 12v in on position UNTIL i install it on the coil and it drops to 4v at the coil terminal. checks ~6.5-7v in start position while cranking.

this leads me to believe my resistance wire value has increased over time or has a really bad connection. is the resistance wire one continuous piece or does it break at the firewall? if it breaks at the firewall, what should the resistance be for each run? i am having a hard time following the wire under the dash with the front seats installed.

would the following be a good test: run 12v through a toggle switch directly to the coil, start the motor, open the switch and see if it idles on it's own. i would just have to close the toggle switch to bring the coil back to 4v and the motor would die on it's own right? any other things to worry about other than temporarily running the coil hot?

if this works, i guess i would have to remove the seats and track down the high resistance value. probably a poorly crimped butt connector somewhere. any other suggestions?

 

[Mercury Mike]

Might be a bad coil.

 

[CobraSix]

Some 65's did have 6v's to the coil stock, so you may close to the right voltage if you did not replace the ballast resist wire with a normal one. My first guess is that.

Outside that, see if you can test the alternator, you might not be putting out enough and your battery may be low. Also check to see if you do have a battery problem.

The wire is not continous if I recall (I'm at work), it goes through the firewall connection.

Slade

 

[goinbroke2]

Hot wire the coil, that just eliminated the whole electrical system and if it runs good, start looking for a broken/bad connection/etc.

Your sure it's not the carb or timing eh? Timing too far retarded will do that too. So will a carb that is not adj right (float, mixture,choke,etc)

 

[Bort62]

If the wire to the coil is at 12v unconnected and goes to 4v as soon as you connect it, it is possible that there is unanticipated resistance upstream of the coil, but it could also be a short in the coil causing it to draw more current than it typically does.

measure the resistance from the coil wire back to the battery +. I would also guess that, if you are seeing 7v at cranking, your coil is drawing more current than it should.

This is all, of course, only applicable if you dont have a 6v system.

 

[mceachrw]

got some quality time with a multimeter tonight. also followed the wiring from the ignition switch to the coil. i found a resistance wire AND a ballast resistor. i guess the previous owner had it setup 6v with a pertronix? could that have ever worked? here is what i found, hope the ascii art displays ok on your end:

inherited setup, did not check voltage on each side of ign switch, will pull switch and check there tomorrow

12.0v___?______?_______8.0v_____4.5v____4.4v
batt____·_ign.sw_·__/\/\/\__·__/\/\/\__·______coil
|_______________1.8 ohm___1.5 ohm________|
|_______________3.4 ohm total_____________|


with the ballast resistor shorted, did not check voltage on each side of ign switch, will pull switch and check there tomorrow

12.0v___?______?_______6.5v_____6.5v____6.4v
batt____·_ign.sw_·__/\/\/\__·__/\/\/\__·______coil
|_______________1.8 ohm___shorted________|
|_______________1.9 ohm total_____________|

i expected to see ~8v at the coil after shorting the ballast resistor. guess i'll see if there is something going on at the ign switch. i saw one of those noise suppression filters spliced in somewhere. if i don't find anything there, i'll swap coils this weekend. trying to keep costs down.

after the coil, my total would be getting real close to what a ds2 setup would cost. i could probably return the new cap, rotor, and wires because i made sure to keep them clean. should i ditch the lom now, plug the scv on the 1940, and go ds2? this would save me the headache of dealing with all vac advance down the road.

 

[LEROY POLL]

HELLO MCEACHRW( WHAT'S YOUR NAME?)

....THOSE FIGURES DON'T LIE!!!

.....EVERYTHING IS CORRECT FROM YOUR NUMBERS. YOU WILL HAVE TO BYPASS THE RESSISTOR WIRE. IT DROPS THE VOLTAGE TO ABOUT 6-8 VOLTS. WITH THE RESSISTOR IN LINE IT SHOULD BE WHAT YOU HAVE.

.....I THINK THE INSTRUSTIONS SAY TO REPLACE THE WIRE. I WOULD JUST RUN AN ANOTHER WIRE IN PARALELL WITH A 1.2 OHM RESSISTOR. THAT WILL GIVE YOU UP TO 10 AMP MAX. TO THE COIL.

.....A SHORTED COIL WILL ALWAY BE SHORTED SO IF IT RUNS WITH MORE VOLTAGE .... COIL IS GOOD!!!

.....YOU STILL MIGHT HAVE MORE PROBLEMS.. BUT THIS WILL MAKE IT RUN.

LIVE IN GRACE

LEROY POLL

 

[CobraSix]

If I recall correctly, Pertronix can run on 6Vs. I think they updated it. I may be mistaken though.

Any change in how the car was running? Did you get a chance to test it?

As far as DS2, you can make that set up real cheap. Mine was a little more because I went with a fancy MSD Digital 6+. Go with a GM module and I think the cost is are $100.

But, even with that, you'll still have to remove or bypass the resistor wire, DS2 requires 12Vs.

Slade

 

[mceachrw]

i'll have to wait till this weekend to fire it up. i have a temporary redneck fuel cell (read that as gasoline in a garden sprayer) that i will NOT run in my garage. don't want a garage fire taking my house with it.

 

[mceachrw]

i am now completely familiar with all ignition related wiring. i followed every wire looking for a bad connection, etc. i could not find anything wrong with the wiring other than the temp sensor was shorted to ground, so i disconnected it.

the only thing i found strange was the voltage on the negative side of the coil. with 6.5v and the pertronix wired, i was getting around 0.5v to ground at the negative side of the coil. if i rotated a magnet in front of the pertronix, it would go to 0v as it should. shouldn't the voltage be much closer to the 6.5v on the positive side of the coil?

anyway, i ran a 25' jumper wire (old extension cord) bypassing the resistance wire and ballast resistor and end up with around 11v at the coil. engine would now idle on it's own, but would not continue running after revving to higher rpms and letting off the gas.

at least i know the engine will idle and it is something in the ignition. since the pertronix passed the bench test, i'm guessing coil. i just bought a complete, working ds2 setup off ebay. i'll wire in that coil and test before making the swap to ds2.

 

[CobraSix]

Correct me if i"m wrong, but if you ran a jumper wire and got 11V's to the coil, then you need to replace your resistor wire, the problem isn't the pertronix. You'll have to get 12Vs to the coil even with a DS2.

THe other problem is very likely carb related.

Slade