where am I losing voltage at?

[nrt69]

Im having a problem getting enough "juice" to my plugs to fire up my car. If i run a wire from the batt to the coil it will fire right up. it starts up for a while by itself after I do this but eventually gets hard to start and then wont start at all.
My buddy was measuring volts while i turned the key so I dont remember the exact volts at the various locations (alt, coil, volt reg, etc) with the key on and when cranking but the highest amount around the coil and volt reg was around 7-8 volts. Batt is putting out 12-14 volts.

heres my set up:
new MSD eCurve distrib (requires 12 volts)
new MSD blaster coil
ballast resistor bypassed
new volt regulator (pre-70)
new alt
new battery
new plug wires
starter relay is of unknown age

other factors:
i have a higher 78amp alternator and my ammeter gauge has been seeing almost 20 amps under throttle for a month or two.
it gets a constant 5 amp charger at idle.
same symptoms happened to me early this year and it turned out to be a bad battery but i have a new one now.

Any suggestions on where to start looking for the power drop?

[68neverlate]

it starts up for a while by itself after I do this but eventually gets hard to start and then wont start at all.

Hi nrt69,

Can you provide more details about this ie:

1)  Does it only start when connecting a wire directly from battery to coil? 
2)  Does it stay running once it does start?
3)  When you say it gets hard to start and then won't start at all, are you talking about when you have a direct wire from battery to coil?  Or??

I remember you having some charging issues in another thread where you mentioned that you would be doing some wiring modifications to handle the extra power from your alternator... did you complete those mods??  If so, which mod did you do?

Ah, electrical....   

[nrt69]

1 no. right now its starting without doing that each time
2 yes
3 no. i only used the wire to jump it once and started it a few times since this weekend unassisted. eventually the car will "lose spark to the plugs". It will first have a weak spark and barely light up the gas sometimes causing it to backfire through the carb. then eventually the spark completely goes away and it do anything. the last time this happened in JAN it was from a bad battery and alt. all that stuff has been replaced now.

my other charging issue was resolved when i grounded the alt. now my 78 amp alt charges too much so ill go back to a 60 amp alt or maybe do the mods eventually.
before i can do anything to the car i need to make it reliable enough to start up when i need it to. i havent done any wiring mods yet.

[nrt69]

update:

my brown ground wire coming off the starter relay on the fire wall is VERY loose. A friend with a 70 Challenger noticed it this weekend when we were troubleshooting but he just pushed it in tighter and we moved on to some more voltage checks.

today i drove the car and returned home, parked it, waited a few minutes, then tried to start it again. nothing. i touched the ground wire on the relay and it almost fell off. i made it tigher, got in the car and it fired right up. im going to play with it some more when i have the time this week but im thinking it may be that loose ground wire.

could a loose ground wire prevent spark from getting to the plugs???

[68neverlate]

No, not that brown wire (starter relay)... if you have any issues with that brown wire, your starter won't engage when you turn the key.

If the issue is that not enough voltage is getting to the spark plugs, I'd turn your key in the ignition to the run (not start) position (engine not running) and take a voltage reading on the wire that feeds your MSD ignition (the one asking for 12 volts).  If that's not 12 volts, then it's a problem with the wiring between the battery and that spot.  If you are getting 12 volts there, then I'd double check to make sure your ignition and coil are wired correctly...        

[Big Sugar]

Did you ever get this resolved ?  Im wondering cause im floating in the same boat,  weak spark and intermitant, ive got 7.5 volts at the coil and im reading 1.5 ohm risistance at the ballast   Swapped out my ecm still no improvement, could it be a bad coil lead ?  Somthing is out of sorts... Dull intermitant spark at the plugs as well, put on my old dist cap,,,, still no change ?



Ron

My battery is in the trunk, have installed 0 gauge ground from the head to the chassis all clean surfaces, my ecm also has a ground strap to the valley pan ...should i ground the ecm to the chassis or is the block the better choice ?


Ron again

[Big Sugar]

Bump