5 volts across coil and ballast
#929983
02/15/11 11:12 PM
02/15/11 11:12 PM
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Joined: Jan 2003
Posts: 660
River Falls, WI
urdustd
OP
mopar
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OP
mopar
Joined: Jan 2003
Posts: 660
River Falls, WI
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I've been searching throughout the electrical and fuel systems on my small block trying to figure out why it won't idle with out rattling (sounds like occasional dieseling). Well I finally pulled out the multimeter and I only have 5 volts across the coil and ballast resistor. I figured I would have 12.8V minus the drop across the ballast, so maybe 10 or so volts.
The car is a 74 Duster with dual field alternator, electronic voltage regulator, MP Orange box, single ballast and a MP electronic distributor and a Blaster 2 coil. Prior to my new findings above, I swapped coils, ballast, cap, wires, ECU and regapped and check resistance across the pickup coil. None of these changes made any difference to how it ran.
Does anyone have any idea why the voltage is so low at the coil? I visually checked the wiring, but everything looks pretty good as the engine harness was replaced 8-10 years ago.
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Re: 5 volts across coil and ballast
[Re: RapidRobert]
#929985
02/16/11 01:16 AM
02/16/11 01:16 AM
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Joined: Jan 2003
Posts: 660
River Falls, WI
urdustd
OP
mopar
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OP
mopar
Joined: Jan 2003
Posts: 660
River Falls, WI
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Ran great than I pulled engine to fix leak in oil pan, changed converter, steering box and headers. Put engine back in and have had this idle issue ever since. Seems fine above 2000 rpm, below it seems to spark knock. Initially intermittently as in every few seconds, as it warms up seems to be almost constant, like a dieseling engine. Above 2000 rpm seems just fine.
74 Duster 360 - 10:1 compression 360, Hughes 2430 cam, air gap, Edelbrock 750 carb. It took me a few months to get all the work done (long story), so I pumped old fuel from tank (probably a gallon or so left) and refilled with 50/50 mix of 100 and 91 octane unleaded.
Making me nuts....
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Re: 5 volts across coil and ballast
[Re: urdustd]
#929986
02/16/11 01:28 AM
02/16/11 01:28 AM
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Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
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it's not a spark knock, I think I've heard it b 4 it's like a hiccup where it misses and a shudder at the same time for a split second ??. Is that it or something else? Trying to get a handle on what it's doing
live every 24 hour block of time like it's your last day on earth
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Re: 5 volts across coil and ballast
[Re: urdustd]
#929988
02/16/11 01:53 AM
02/16/11 01:53 AM
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Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
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jump full 12V to coil positive pri terminal to bypass the ballast for 5 seconds to elim/confirm that. Gotta hit the hay it's 11PM here, I'll sleep on it.
live every 24 hour block of time like it's your last day on earth
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Re: 5 volts across coil and ballast
[Re: RapidRobert]
#929989
02/16/11 02:03 AM
02/16/11 02:03 AM
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Joined: Jan 2003
Posts: 660
River Falls, WI
urdustd
OP
mopar
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OP
mopar
Joined: Jan 2003
Posts: 660
River Falls, WI
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I'll give it a shot tomorrow...late here too. I'll see if I got a video from when I had the hiccup. Right after reassembly. Probably should video what it's doing now too. A picture/video is worth hundreds of typed words. Video Link Thanks
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Re: 5 volts across coil and ballast
[Re: urdustd]
#929990
02/16/11 02:09 AM
02/16/11 02:09 AM
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Joined: Oct 2010
Posts: 606
Montana
Yancy Derringer
mopar
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mopar
Joined: Oct 2010
Posts: 606
Montana
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Quote:
I only have 5 volts across the coil and ballast resistor. .........................
Does anyone have any idea why the voltage is so low at the coil?
You need to measure the voltage
ground probe on the battery negative
pos probe on the "top" of the ballast --coming from the switch.
Voltage RUNNING then compared across battery should be within .2--.3v that's THENTHS of volts.
If not, you have problems with the bulkhead connector going INTO the dash, or the connector on the ignition switch or the switch itself, or the bulkhead connection coming OUT of the dash. All these things add up to "voltage drop."
If you have not modified the ammeter or bypassed it, there's a couple MORE places for drop to occur.
As someone said, make up a clip lead, and hotwire direct from the battery to the switch side of the ballast and see it the problem disappears.
Would not be a bad time to make sure charging voltage is within limits.
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Re: 5 volts across coil and ballast
[Re: urdustd]
#929991
02/16/11 05:01 AM
02/16/11 05:01 AM
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Joined: Jan 2003
Posts: 5,445
So Cal
Sinitro
master
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master
Joined: Jan 2003
Posts: 5,445
So Cal
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Quote:
I've been searching throughout the electrical and fuel systems on my small block trying to figure out why it won't idle with out rattling (sounds like occasional dieseling). Well I finally pulled out the multimeter and I only have 5 volts across the coil and ballast resistor. I figured I would have 12.8V minus the drop across the ballast, so maybe 10 or so volts.
The car is a 74 Duster with dual field alternator, electronic voltage regulator, MP Orange box, single ballast and a MP electronic distributor and a Blaster 2 coil. Prior to my new findings above, I swapped coils, ballast, cap, wires, ECU and regapped and check resistance across the pickup coil. None of these changes made any difference to how it ran.
Does anyone have any idea why the voltage is so low at the coil? I visually checked the wiring, but everything looks pretty good as the engine harness was replaced 8-10 years ago.
What is the resistance of the ballast resistor?,
The original was 1.25 Ohms but with the Blaster II coil you should be using a 0.25 Ohm..
Big difference in coil voltage between these.
Just my $0.02... 
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Re: 5 volts across coil and ballast
[Re: Mr.Yuck]
#929994
02/16/11 10:37 AM
02/16/11 10:37 AM
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Joined: Jan 2003
Posts: 660
River Falls, WI
urdustd
OP
mopar
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OP
mopar
Joined: Jan 2003
Posts: 660
River Falls, WI
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I've tried 3 different ballast resistors, two Wells Ampco (4-wire) and 1 MSD (2 wire, low resistance) and they all run the same. I didn't check the difference in voltage at the coil as there really didn't appear to be needed as it still knocked. The voltage readings I got were with the MSD ballast. I need to check the charging voltage to rule out the alternator and voltage regulator. I will also disconnect and clean all the bulkhead and other connectors in the harness to be sure I don't have a massive voltage drop somewhere in it. I will also disconnect the coil and check voltage, but I vaguely remember checking years ago and it was ~11V, but who knows for sure as I'm getting old and can't remember schmidt, if you know what I mean! I appreciate everyone's input so don't be shy if you have an idea. Added YouTube link to video, listen to beginning (idle) of video for the knock YouTube
Last edited by urdustd; 02/16/11 10:57 AM.
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Re: 5 volts across coil and ballast
[Re: can.al]
#929997
02/16/11 11:48 AM
02/16/11 11:48 AM
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Joined: Jan 2003
Posts: 5,444
Indiana
YO7_A66
master
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master
Joined: Jan 2003
Posts: 5,444
Indiana
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I had 4.5 volts at the coil (when I was running a ballast setup) which resulted in a poor and inconsistant idle. So I also cleaned all of the connectors and replaced the ones that had too much of the original wire showing before the terminal. Then I too cleaned the bulkhead fitting and then had 8+ volts.
Since then, I now have a voltage guage to read the coil voltage and one that reads the battery voltage. This way I can reference both voltages from inside of the car while driving when needed. They are both hidden inside of the glove box.
1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)
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Re: 5 volts across coil and ballast
[Re: YO7_A66]
#929998
02/16/11 12:36 PM
02/16/11 12:36 PM
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Joined: Jan 2005
Posts: 3,344
Central TX
roe
master
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master
Joined: Jan 2005
Posts: 3,344
Central TX
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what is the best way to disconnect all the connections at the bulkhead without damaging the connectors? I may need to pull mine and clean/grease rhem with a good dielectric
roe
1971 Plymouth Satellite
408/904 8 3/4 3.23 SG
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Re: 5 volts across coil and ballast
[Re: roe]
#929999
02/16/11 12:46 PM
02/16/11 12:46 PM
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Joined: Jan 2003
Posts: 24,562
Brookeville, Md
Mr.Yuck
Not enough dumb comments...yet
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Not enough dumb comments...yet
Joined: Jan 2003
Posts: 24,562
Brookeville, Md
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Quote:
what is the best way to disconnect all the connections at the bulkhead without damaging the connectors? I may need to pull mine and clean/grease rhem with a good dielectric
roe
outside (engine side) is pretty easy just be careful with the tabs as they get brittle w/ age. Under the dash can be a PITB, just take your time and be care not to yank on anything and they should all come out. I took a small flat head screw driver and folded a small piece of sand paper to it..I ran it in and out of every contact point, made sure everything was nice and shiney before I sprayed it and pluged it all back together.
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