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Have a stock dodge RV with a 360 engine which has been hard to start. so far I have replaced the ballast resistor pack. I know that it has 2 resistors one while cranking and another while running. With the new resistor it starts right up...... so far.
The problem is that when I measure the voltage across the coil terminals I get 3.8 volts. If measure from the + terminal to engine block I get almost 9 volts. I have a solid ground to the ignition module body.
Which is correct?
or
Do I have a bad ignition module?
What are your thoughts please?
9 to the block is correct. Basically the ballast is bypassed during cranking start to give as much voltage to the coil during start as the starter will draw a lot of current and drop the voltage to the coil. When running the ballast resistor drops the voltage to help the coil last, 12-14 constant voltage will damage the coil.
I tracked down poor engine performance to the pickup coil and reluctor. The reluctor was chipped in several place from poor gap. Once I fixed the gap to ,008 it ran better but would still shut down all by itself. LOL
So I began to monitor the output voltage of the pickup coil this morning with a scope and saw fluctuations from 20 volts to 29.2 volts. At 29 volts the RPM would increase and slow down at 20 volts. below 20 volts the engine would die. Ordered a new distributor. I will make the measurements again when the new part comes in.
Last edited by jd_boggs; May 17, 2021 at 06:36 PM.
I tracked down poor engine performance to the pickup coil and reluctor. The reluctor was chipped in several place from poor gap. Once I fixed the gap to ,008 it ran better but would still shut down all by itself. LOL
So I began to monitor the output voltage of the pickup coil this morning with a scope and saw fluctuations from 20 volts to 29.2 volts. At 29 volts the RPM would increase and slow down at 20 volts. below 20 volts the engine would die. Ordered a new distributor. I will make the measurements again when the new part comes in.
20 Volts Dose not sound correct..... Something is way wrong...
Yes, my measurement were very wrong. I think the oscilloscope I was using was set up wrong because when I installed the new distributor my voltage was only 7 volts. 7 volts is more believable than 29 from a coil and magnet. The engine runs great starts easily. The scope has several functions that I don't fully understand and I was only trying to monitor the amplitude of the waveform until the engine died and record the last voltage. Going to experiment more on the bench using 4 GM HEI and the Mopar distributor I have. I plan to spin the distributor shaft with an electric drill and see what I can learn from this.
350-550 ohms for the reluctor........ I think? but I am not sure (Been a Long Time) that the reluctor will only generate something like 1MAV "Milli-Amp-Volt" @0.008 air gap.... But dont hold me to the fire on that note...
I made a test stand to measure reluctor voltage output on a distributor assembly.
Method:
I placed a pulley on the 1/2" distributor shaft with a belt going to a sewing machine motor (with foot peddle)
Results for each distributor assembly with reluctor:
Mopar 1975 .... 580 millivolts
GM HEI #1 ...388 millivolts
GM HEI #2 ... 620 millivolts
GM HEI #3 ... 816 millivolts
GM HEI #4 ...952 millivolts
scope leads attached to module sewing machine motor and distributor
