Re: Voltage at coil (+)? Might be on to something...
[Re: Schwinger]
#681318
04/26/10 10:21 PM
04/26/10 10:21 PM
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Joined: Mar 2003
Posts: 15,493 the boonies
aarcuda
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I Live Here
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Posts: 15,493
the boonies
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ya, thats a problem. i like to see around 7v at the coil
It's got a cop motor, a 440 cubic inch plant, it's got cop tires, cop suspensions, cop shocks. It's a model made before catalytic converters so it'll run good on regular gas.
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Re: Voltage at coil (+)? Might be on to something...
[Re: Schwinger]
#681319
04/26/10 10:25 PM
04/26/10 10:25 PM
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Joined: Sep 2007
Posts: 14,889 up yours
Supercuda
About to go away
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About to go away
Joined: Sep 2007
Posts: 14,889
up yours
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11.3V tells me the charging system, isn't.
When it's running 13.8V is more like what you should see. It will vary a bit, but should be in that ballpark. Low voltage tot eh ballast means low voltage out adn low voltage at the coil.
Fix that first, then see what's at the coil. If this is a dual ballast resistor you probably have it hooked up to the wrong side, 2.5 Ohms is way too much.
How voltage drop works is simple to figure. Measure from the ballast input to ground (no voltage applied). Subtract the ballast resistance, in this case 2.5 ohms. The difference is the coil resistance. Let's say both are 2.5 ohms, then the voltage at the coil + will be half the voltage at the input to the ballast, the equally drop the same voltage. If the coil resistance was 1.25 ohms and the ballast is 2.5 then the ballast would drop 2/3 of the voltage and the coil the remaining third, so at 12V into the ballast you would see 4 volts at the coil +. IOW, the percentage of resistance the coil has in the circuit is the same percentage of voltage dropped across the coil.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
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Re: Voltage at coil (+)? Might be on to something...
[Re: dave571]
#681323
04/27/10 12:19 AM
04/27/10 12:19 AM
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Joined: Jan 2004
Posts: 2,362 Paso Robles, CA
Schwinger
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OP
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Paso Robles, CA
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OK, I dug around the garage and found a ballast that reads .7 ohms. Might be the one that came with the MSD coil, I dunno. Still seeing less than 5 volts at the coil! Went over the wiring to the ballast and the box, seems OK. Jumpered the ballast out, I get 8.3v at the coil, engine off. Was tempted to start it just to see, but didn't want to fry my only chrome box. BTW, are ballasts rated hot or cold? The .7 ohm one read more like 1.5+ after running the engine a bit.
69 GTO | 72 Chevy Highlander | 56 Ford 850 | Lawn-Boy 10518 | 96 Honda XR250R
Fresh out of Mopars
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Re: Voltage at coil (+)? Might be on to something...
[Re: Schwinger]
#681324
04/27/10 01:19 AM
04/27/10 01:19 AM
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Joined: Dec 2005
Posts: 4,280 State of Fascism
52savoy
master
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master
Joined: Dec 2005
Posts: 4,280
State of Fascism
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Get a new ballast... and then if you still have a problem... Check voltage from the ignition switch "on" position. Check for loose/bad wire terminals. Start at the beginning(starter relay power) and go forward..check the fusable link volts at the firewall bulkhead and then the ignition switch power wires. No MSD box?
Last edited by 52savoy; 04/27/10 01:33 AM.
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Re: Voltage at coil (+)? Might be on to something...
[Re: BigBlockMopar]
#681327
04/27/10 05:15 PM
04/27/10 05:15 PM
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Joined: Apr 2005
Posts: 12,271 Overpriced Housing Central
RobX4406
I Live Here
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I Live Here
Joined: Apr 2005
Posts: 12,271
Overpriced Housing Central
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Wow look what the cat dragged in... LOL Sup JC??? Check it when running. Sounds like it may be a bad wire somewhere. They don't run well on 3 volts at the coil... As a test, you might try running a hot lead right to the ballast, opposite side of coil lead, and see if that helps.
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Re: Voltage at coil (+)? Might be on to something...
[Re: Schwinger]
#681328
04/27/10 07:23 PM
04/27/10 07:23 PM
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Joined: Sep 2007
Posts: 14,889 up yours
Supercuda
About to go away
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About to go away
Joined: Sep 2007
Posts: 14,889
up yours
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Quote:
OK, I dug around the garage and found a ballast that reads .7 ohms. Might be the one that came with the MSD coil, I dunno. Still seeing less than 5 volts at the coil! Went over the wiring to the ballast and the box, seems OK. Jumpered the ballast out, I get 8.3v at the coil, engine off. Was tempted to start it just to see, but didn't want to fry my only chrome box.
BTW, are ballasts rated hot or cold? The .7 ohm one read more like 1.5+ after running the engine a bit.
With the ballast jumpered out you should see battery voltage at the coil. Since you are not you need to find out where you lost the voltage, probably at the ignition switch. I would measure the switched 12V at the ignition switch and see what that is, if it's low measure the voltage into the switch. If the switched 12V is OK at the ignition switch then the wire between the switch and the balast is the issue.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
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So much for that theory.
[Re: 71_deputy]
#681331
05/01/10 09:25 PM
05/01/10 09:25 PM
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Joined: Jan 2004
Posts: 2,362 Paso Robles, CA
Schwinger
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Antisocial
Joined: Jan 2004
Posts: 2,362
Paso Robles, CA
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So I went looking for the cause of the low voltage again today. Found that the coil (+) side of the ballast actually showed shorted to ground! Traced the other wire there back to the ignition switch, where it also goes off to the gauge cluster. I have a lot of unused wires in the dash, so I just nipped that wire off. Presto, short to ground gone! No change in voltage at coil. What??? Found that I lose about 1v turning the key on, even at the alternator post. Don't get that, either. The only other wire that goes to the ballast is the starting bypass, so I clipped that one to test it. Voila, 11+v at the coil! Got it to start by releasing the key slowly from 'crank'. STILL RUNS CRAPPY Closed up the garage. At this point, I'm so frustrated and angry with my own lack of ability to diagnose this, I'm ready to push the car and all my mechanic tools down to the end of the driveway with a big "FREE" sign on them.
69 GTO | 72 Chevy Highlander | 56 Ford 850 | Lawn-Boy 10518 | 96 Honda XR250R
Fresh out of Mopars
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