No spark at coil.

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C

Casaroonc

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Hi everyone,

New to your forum, & the 75 Dart SE I just bought for my son.

I drove this car 2 hours home on Friday, & around the neighborhood Friday & Saturday with no problems. My intentions were to go through everything before I made this my sons daily driver. However on Saturday after my boys & I finished doing our first round of cleaning the car up it wouldn't start. After further inspection there was no spark at the coil. So here are some of the facts that I have found.

-Dual Ballast resistor was new but installed upside down.-Corrected
-ECU was a 4 pin, Harness is a 5 pin. I had a 5 pin that came with the car so I switched it out.
-I did OHMS test on all the harness lines & everything checked out.

This is where my question lies
-+side of Coil shows within 1 Volt of Battery not connected to the coil however when connected to the coil the voltage drops to around 3.5 Volts.

Any thoughts. & at some point I think I will upgrade the electronics.
 
If you are measuring the coil voltage, with ballast connected up, and the key "in run" that is normal. You are seeing the drop through the ballast.

Two checks you need to make

Turn key to "run" engine off. clip your voltmeter to the "key side" of the ballast and compare that to battery. You should be within 3 tenths of a volt or better

Clip voltmeter to coil + and crank engine using the key. You should be within 3-4 tenths of a volt of battery

Easy way to measure this voltage drop directly is to clip the other meter lead NOT to ground, but rather, the battery positive post. This will directly show the drop

Try removing/ installing the distributor, ECU, and resistor connectors several times, to "scrub" them clean, and to "feel" for tightness

CHECK the reluctor gap in the distributor. Hook your meter to the two dist. terminals with your meter on low AC volts, and crank the engine. You should get about 1V AC if not replace the pickup coil and reluctor. Inspect them for rust/ debri/ "strike" damage.

You say you had the resistor upside down. The diagram below gives the correct orientation. NOTICE the "U" shaped opening at one end of the resistor, which orients it correctly

Be aware that a 5 pin ECU MUST have a 4 pin resistor, but

a 4 pin ECU can use EITHER 2 or 4 pin resistor -- 1/2 is just not used

You cannot ID a box by the number of pins. Some 4 pin boxes have a dummy 5th pin. YOu have check continuity to tell the difference.

IF possible use a 4 pin box --better design.

(From "MyMopar")

Ignition_System_5pin.jpg
 
"Two checks you need to make"

I will Check these things these this week. The car is at my workshop (wood shop) & I'm not at it to check tonight.



"You say you had the resistor upside down."

After the car wouldn't start I started to look around & at a book I have for my truck, that covers the 70's models & saw right away that the guy i had bought it from had put it in upside down. The firewall even has a bump in it for the notch. Also the Resistor was very hot after we were cranking the car.

"Be aware that a 5 pin ECU MUST have a 4 pin resistor"

it is


"IF possible use a 4 pin box --better design."

I was wondering if before I go any farther if I should just switchover as some are advocating on this site.

Thanks
 
"Two checks you need to make"

Done

"Turn key to "run" engine off. clip your voltmeter to the "key side" of the ballast and compare that to battery. You should be within 3 tenths of a volt or better"

- At least 1.5 volts less at the key side of the ballast.

"Clip voltmeter to coil + and crank engine using the key. You should be within 3-4 tenths of a volt of battery"

- + side of the coil was at 3 volts, then drops to 2.24 when cranked.


"Easy way to measure this voltage drop directly is to clip the other meter lead NOT to ground, but rather, the battery positive post. This will directly show the drop"

- did this & got 4.4 volts when cranked.



"Be aware that a 5 pin ECU MUST have a 4 pin resistor, but

a 4 pin ECU can use EITHER 2 or 4 pin resistor -- 1/2 is just not used"


- Tried all of the above test with both the 4 & 5 pin boxes.

any thoughts as to why my voltage is so low at the ballast/

Thanks


[/QUOTE]
 
Be certain you are measuring the voltage at the KEY side of the ballast and not the COIL side.

The "ignition run" (dark blue) coming out of the bulkhead connector supplies

the key side of the ballast

the blue field wire to the alternator

the "I" terminal on the regulator

the electric choke heater if used

So another point to check is the blue wire down at the alternator field.

Your voltage drop suspects are the bulkhead connector, the connector on the ignition switch, the switch itself, problems at the ammeter or the "in harness splice" which supplies the ignition switch, or the battery/ alternator infeed wires, again, coming through the bulkhead connector
 
"Be certain you are measuring the voltage at the KEY side of the ballast and not the COIL side"

I checked both sides to be sure.
 
Sounds like it's not firing.
 
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