will better English give me more voltage? Haha, you're right that's what I meant. The truck turns over and over, but won't run until I release the key.
Ignition voltage
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From: Minneapolis
Ignition voltage
Hey guys. I'm new to this forum as a member, but I've been reading and doing research from the threads here ever since I bought my truck - 1980 F250 custom 400 engine. Maybe you can help me out here...
Recently the old beast wouldn't start. The starter would engage, but would just crank to infinity and never start. Started replacing stuff - the coil and the ignition switch. Wasn't working, so I dug deeper and found that I wasn't getting a voltage on my coil during start. Found an internal break in my brown/pink start wire after the ignition switch but before the merge with the resistance "run" wire, so I replaced it. Now I get voltage during start and run, but it still wont start unless I release the key to the run position. During start I get slightly less than 10v and during run I get a full 12.5v. Does my starter really pull the voltage down THAT much? And isn't the point of the resistance wire to drop the voltage to my coil during run to something around 8v? My coil says "12V FOR BREAKERLESS IGNITION WITH EXTERNAL RESISTOR 016V" is it supposed to run off 12v during run?
Recently the old beast wouldn't start. The starter would engage, but would just crank to infinity and never start. Started replacing stuff - the coil and the ignition switch. Wasn't working, so I dug deeper and found that I wasn't getting a voltage on my coil during start. Found an internal break in my brown/pink start wire after the ignition switch but before the merge with the resistance "run" wire, so I replaced it. Now I get voltage during start and run, but it still wont start unless I release the key to the run position. During start I get slightly less than 10v and during run I get a full 12.5v. Does my starter really pull the voltage down THAT much? And isn't the point of the resistance wire to drop the voltage to my coil during run to something around 8v? My coil says "12V FOR BREAKERLESS IGNITION WITH EXTERNAL RESISTOR 016V" is it supposed to run off 12v during run?
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From: Virginia
Yes the starter can pull the voltage down that much. Lots of factors such as the health of your battery and the quality of your battery cables affects it.
Sometimes people have this problem when it coughs when they let the key up, but won't run, and it turns out to be something wrong with the ignition module. You should keep a spare behind the seat anyway.
Sometimes people have this problem when it coughs when they let the key up, but won't run, and it turns out to be something wrong with the ignition module. You should keep a spare behind the seat anyway.
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From: Minneapolis
Well it doesn't cough it starts when I let go of the key! Basically there's not enough voltage to the coil to crank it over when the starter is engaged, but when I release the key to the run position the 12 volts allows it to kick over and keep the engine going. Kind of hard to time it just right... and shouldn't really be happening at all I'd say. Bad starter (drawing too much voltage)?
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From: Angier, NC
Echotop, welcome to the forum.
You keep getting "crank" and "turned over" mixed up or something, they are the same thing. You "crank" or "turn over" the motor to try and start it.
From what I think you are saying is when you crank or turn over the motor to start it it will only run when you let go of the key from cranking/turning over.
Oh I think the crank went out with the model A Ford lol
Dave ----
You keep getting "crank" and "turned over" mixed up or something, they are the same thing. You "crank" or "turn over" the motor to try and start it.
From what I think you are saying is when you crank or turn over the motor to start it it will only run when you let go of the key from cranking/turning over.
Oh I think the crank went out with the model A Ford lol
Dave ----
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From: Virginia
That can be a symptom of a bad ignition module. With 10v on the coil the engine should start and run.
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From: Minneapolis
So it may be the ONE component in the ignition system I haven't replaced since I bought the truck? That would make sense I suppose, and just my luck! My other question was whether or not I should read 12 volts at the batt terminal on the coil when the engine is running? I know some older vehicles have less voltage while running to save the coil (6-8 volts), but some run at 12 volts regardless. Since there's a 1.1 ohm resistance wire, should my voltage reading be less? Just want to make sure I'm not destroying my coil here... Thank you Franklin2 for your suggestion so far 
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Cargo Master
Joined: Mar 2008
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From: Washington
So it may be the ONE component in the ignition system I haven't replaced since I bought the truck? That would make sense I suppose, and just my luck! My other question was whether or not I should read 12 volts at the batt terminal on the coil when the engine is running? I know some older vehicles have less voltage while running to save the coil (6-8 volts), but some run at 12 volts regardless. Since there's a 1.1 ohm resistance wire, should my voltage reading be less? Just want to make sure I'm not destroying my coil here... Thank you Franklin2 for your suggestion so far
The best test is to put the key ON, engine not running, and check the coil positive voltage. it should be around 7-8 volts.
Did you buy a stock DS2 coil with a primary resistance around 1.2 - 1.3 ohms?
What is the voltage across the battery terminals at idle ... 14.5 volts?
Jim
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From: Minneapolis
Hey there Jim! Thanks for responding. Using a Fluke 85 I just took some readings. Battery voltage at idle: ~14.59v. Primary coil resistance: 1.4-1.5 ohm. Key on (engine not running) coil positive voltage: ~7.39v. Now that's what I expected it should be, so maybe I was making a rookie mistake and reading the coil while the engine was running? I'll be picking up a new ignition module today and swapping that out. Hopefully that will fix my starting woes. I'll let everyone know what happens!
Cargo Master
Joined: Mar 2008
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From: Washington
The voltage readings all look good.
At idle the voltage at the coil positive is a square wave with the low point at ~7.39 volts and the high point at ~ 14.59 volts. The meter will attempt to average this based on the duty cycle (dwell) of the square wave... in your case 12 volts.
In the big picture, as long as you are not getting 14.59 volts at the coil positive at idle the resistor wire is working.
Next test is coil positive voltage, key in start position, engine not running.
To keep the starter from engaging and dragging down the voltage, remove the small push-on connector from the starter solenoid.
Your starter solenoid should have 2 large terminals and one small terminal. If so, the full voltage bypassing the resistor wire to the coil positive then come from the ignition switch.
You should see the volt meter go from 7.39v (key ON) to full battery voltage in the start position.
A weak battery or "high draw starter" can drag the voltage down to the point where it wont start.
A good parts store can test the DS2 IGN module... and also the battery and starter.
Jim
At idle the voltage at the coil positive is a square wave with the low point at ~7.39 volts and the high point at ~ 14.59 volts. The meter will attempt to average this based on the duty cycle (dwell) of the square wave... in your case 12 volts.
In the big picture, as long as you are not getting 14.59 volts at the coil positive at idle the resistor wire is working.
Next test is coil positive voltage, key in start position, engine not running.
To keep the starter from engaging and dragging down the voltage, remove the small push-on connector from the starter solenoid.
Your starter solenoid should have 2 large terminals and one small terminal. If so, the full voltage bypassing the resistor wire to the coil positive then come from the ignition switch.
You should see the volt meter go from 7.39v (key ON) to full battery voltage in the start position.
A weak battery or "high draw starter" can drag the voltage down to the point where it wont start.
A good parts store can test the DS2 IGN module... and also the battery and starter.
Jim
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From: Minneapolis
Jim thank you so much for teaching me a bit about the electrics. I hooked up my oscilliscope and everything looked just as you said it would. Yeah my multimeter was definately calculating average voltage then.
Wired up the new ignition module and no surprise it works! Turns over maybe twice then fires away! Not only that but the engine runs a heck of a lot better at cold idle now, couldn't be happier! Well now that I've replaced 90% of my ignition system I hope I wont have any problems for a very long time.
Thanks guys! Cheers
Wired up the new ignition module and no surprise it works! Turns over maybe twice then fires away! Not only that but the engine runs a heck of a lot better at cold idle now, couldn't be happier! Well now that I've replaced 90% of my ignition system I hope I wont have any problems for a very long time.
Thanks guys! Cheers
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Cargo Master
Joined: Mar 2008
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From: Washington
If you still have the oscilloscope handy take a look at the stator output on the ALT, I am guessing it will be a half sine wave. ~20-21 volts peak, but I sold my oscilloscope a long time ago so I can't confirm this.
Thanks
Jim
Thanks
Jim
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From: Minneapolis
Um, there's been a serious breach of forum etiquette. You posted a problem and you got some good advice. Normally that's where it ends, and we are left wondering what finally fixed it. Instead, you came back and updated the thread for everybody's benefit.
If you still have the oscilloscope handy take a look at the stator output on the ALT, I am guessing it will be a half sine wave. ~20-21 volts peak, but I sold my oscilloscope a long time ago so I can't confirm this.
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