Coil problem?

Aspen500

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If you have electronic spark control or lean burn, you are correct. You may want to check the charging system voltage at 2,000-3,000 rpm, to make sure it isn't going too high while driving. It shouldn't go above 14.6 volts max. Above 14 volts at idle is unusually high. Not sure what coil you installed but, does it have printing the side saying "no resistor required" or "External resistor required", or something similar to that? As long as the coil is rated for 12-14 volts constant (no resistor required) the 14 volts is fine. If it requires a resistor, it's made to operate on 7-8 volts (12 volts in "start"), supplying it with 12-14 volts constantly can cause it to overheat and fail.
 

69-

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Fast blinkers? Whats the voltages in your system?
E.g. ground to alternator output stud and in comparison directly at the battery?
 

AJ/FormS

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Fast blinking is not due to over-voltage. Let me rephrase that; I have not seen 14.2volts be a problem. Lots of cars nowadays have charging systems running ~14.2 volts; it is actually quite common.

Fast blinking is usually due excessive draw in the bulb circuit , in the which, the hi-draw causes the bi-mettalic bar inside the old-style flasher to heat up too fast, and then she breaks contact.
The hi-draw could be from wrong bulbs, too many bulbs, faulty bulbs, or a plain old short somewhere including inside the bulbs them selves.

But that old-style flasher eventually just gets worn out.
You can try replacing it with a "HD electronic type" sometimes called a trailer flasher which does not suffer the same malady.
I have seen the short inside the signal switch.
 
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SharkHead

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At rpm rev I am getting 14.4v from the coil and 14.6v from the main post on the alternator.
The coil is an original mopar 4176009.
 

Aspen500

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That voltage is perfect. 14.6 volts is the what the regulator limits voltage to on conventional (non-computer controlled) systems.
 

Hayzoos

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With the Spark Control Computer (Lean Burn) the voltage is controlled on the (-) negative side of the coil from inside the computer. With the electronic ignition the ballast resistor controlling the voltage is on the (+) positive side of the coil. So testing the voltage at the (+) positive side of the coil and the other voltmeter lead grounded is correct for the electronic ignition with a ballast resistor. The equivalent test point with the Spark Control Computer is in the computer so is not as easy to perform. But if you connect the voltmeter to the battery (+) positive and the (-) negative of the coil you should get a proper reading of voltage at the coil on the Spark Control Computer lean burn system. I haven't tested this but the voltage should be in the same range of 6-8 volts. I came up with this by examining the FSM wiring diagrams and knowing that the same external resistor required spec. coil is used in both systems.

The Spark Control Computer lean burn system has the equivalent of a ballast resistor inside the computer. It starts with a direct ground or a higher voltage and runs with a resisted ground or a lower voltage.

They do not generally build resistors into coils. Resistors create heat and excess heat is bad for coils. The coils that run at battery voltage have different windings so the primary can handle the higher voltage. This also means they have different secondary windings to match the primary windings so the resulting secondary voltage is in the proper range for ignition and not too much which would wear away plug electrodes faster.
 

SharkHead

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So I tested coil negative to battery positive and it's running anywhere from three and a half to almost four and a half volts, jumping around a bit even at a steady rate of around 2,000 RPM.
 

Hayzoos

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At first glance those voltage readings seem low. Now I have referred back to the wiring diagram and see the computer has a ground. My next thought is to make sure that ground has not degraded.

The diagram I am referencing states the ground is located at the right rear cylinder head. Test it by meter negative to that ground point and meter positive to battery positive. It should be very close to battery voltage or charging voltage if running.

The block also has to be grounded well and is on the left front of the engine with a cable directly to the battery. While you are at it clean up the battery terminals. There is also a ground for the alternator at the right front of the engine.

Also check the connectors on the computer, poor connection there can impact both the ground path and the coil control.

Copper and most copper alloys' oxides conduct about as well as uncorroded copper/alloy. But certain copper/alloy corrosion such as sulphur (acid rain, battery acid vapors), calcium or sodium (road salt, ocean spray), or whatever may not be as conductive. And iron/steel corrosion AKA rust is definitely not as conductive as uncorroded. Same goes for aluminum and most other metals, corroded not as conductive.

Eliminate poor connections especially grounds, before suspecting any bad parts.
 

AJ/FormS

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Did you do this while the car was running?

Yes, Car was running

Ok so if you connect the coil neg to the batter pos while the engine is running, as per
So I tested coil negative to battery positive and it's running anywhere from three and a half to almost four and a half volts, jumping around a bit even at a steady rate of around 2,000 RPM.

How can the engine even stay running? You are attempting to pump battery voltage into the ECU, backwards thru the coil. This should totally extinguish the incoming ECU signal, making it go from a pulsed 8 volt to a solid 13 volts. IDK how the engine can stay running?
 

Hayzoos

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The connection was made with a voltmeter to check the voltage. The voltmeter has high impedance so no current flows on that connection.
 

AJ/FormS

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Hooked up that way, the battery has the higher pressure, so what you are doing is measuring battery voltage while the ECU is bouncing the coil to ground in tandem with the Magnetic pick up. Whatever numbers you are getting, IMO, are meaningless, for the purpose of diagnosing your system.
 

Hayzoos

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Hooked up that way, the battery has the higher pressure, so what you are doing is measuring battery voltage while the ECU is bouncing the coil to ground in tandem with the Magnetic pick up. Whatever numbers you are getting, IMO, are meaningless, for the purpose of diagnosing your system.
The battery has higher pressure from either it's negative or positive only polarity is reversed. The ballast resister has been moved from the positive side of the coil to the negative in the ECU design. And the positive side of the coil is now directly connected to battery/charging voltage. So you need to measure the ballast resistor side of the circuit to see the lower voltage.

The voltmeter may not be able to respond fast enough though to get a peak reading, since as you mentioned it is measuring the pulsed signal. Here, higher RPMs make that effect even worse. You would need a better voltmeter or an oscilloscope to get the peak reading.
 
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