Re: Ignition question: voltage from coil.
[Re: slowpoke]
#969994
04/10/11 09:24 AM
04/10/11 09:24 AM
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Joined: Jan 2003
Posts: 815
Alexandria, NJ
WayneM
super stock
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super stock
Joined: Jan 2003
Posts: 815
Alexandria, NJ
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What car is it? Is it factory Electronic IGN, or did someone put the kit in?
2014 Durango R/T
2004 Dodge Ram 3500 SRW SLT short quad Cummins 6 speed
1998 Dodge Durango SLT 5.2
1971 Plymouth Duster-
<<<<<MOPAR SPOKEN HERE>>>>>
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Re: Ignition question: voltage from coil.
[Re: slowpoke]
#969997
04/10/11 01:56 PM
04/10/11 01:56 PM
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Joined: Jan 2003
Posts: 815
Alexandria, NJ
WayneM
super stock
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super stock
Joined: Jan 2003
Posts: 815
Alexandria, NJ
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I think you should start by looking at how the ignition system was wired in. Is the ECU getting full battery voltage? I know sometimes it's wired AFTER the Ballast. If this is done, the ECU won't work right. Remove the ECU connector, with the key on and see that you have similar voltage there as the Battery.
Also, That car shoud have a single field charging system. Not as efficent as a dual field('70-up). There are kits out to update- something to consider. One other thing to check is the bulkhead connectors where the charging system passes through to and from the ammeter. With the car idling, to you show a similar voltage @ the back of alternator and @ the battery?
2014 Durango R/T
2004 Dodge Ram 3500 SRW SLT short quad Cummins 6 speed
1998 Dodge Durango SLT 5.2
1971 Plymouth Duster-
<<<<<MOPAR SPOKEN HERE>>>>>
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Re: Ignition question: voltage from coil.
[Re: WayneM]
#969998
04/10/11 03:41 PM
04/10/11 03:41 PM
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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:
Remove the ECU connector, with the key on and see that you have similar voltage there as the Battery.
Sorry I know what you are thinking, but this test is not legit. When you disconnect the ECU, you will have no load on the ignition. You will in fact have an "open ended" harness. Even if the harness had considerable resistance, the meter draws almost no current, and you will show battery voltage OK on both sides.
ONLY WAY to check for voltage drop is WITH THE HARNESS UNDER LOAD, as in, "in operation."
Quote:
. One other thing to check is the bulkhead connectors where the charging system passes through to and from the ammeter. With the car idling, to you show a similar voltage @ the back of alternator and @ the battery?
Sorry, I know what you are getting at, but this is a VERY subjective test----
depending on the current the alternator is putting out, may be almost nothing, there may be zero, some, or a "lot" of voltage drop on this harness. The FACT is that these cars---even when they were new and in good shape--had a certain amount of voltage drop on the (undersized) wire and (undersized) bulkhead connector on that line from the alternator output, through the bulkhead, through the ammeter, BACK out the bulkhead, and to the battery.
IF you had just started the car, on fast idle. so it was charging heavy, I WOULD NOT BE SURPRISED to see nearly a 1 volt drop under those conditions.
Last edited by Yancy Derringer; 04/10/11 10:33 PM.
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Re: Ignition question: voltage from coil.
[Re: WayneM]
#969999
04/10/11 03:47 PM
04/10/11 03:47 PM
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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 think you should start by looking at how the ignition system was wired in. Is the ECU getting full battery voltage?
One way to do this follows:
The "dark blue" ignition run comes directly from the ign switch and powers the ignition system, and the regulator "ign" terminal. In '70 and later cars, it ALSO feeds the alternator field (isolated field), the electric choke if used.
With the car running to simulate "low cruise" stick one probe of your meter directly onto the battery positive post.
Stick the other probe on the IGN terminal of the regulator.
You are looking for a VERY low reading. Zero volts is perfect, anything over .2 (two tenths of a volt) is too much and indicates problems in the "dark blue" "ignition run" circuit. Most likely "usual suspects" are the bulkhead connector, the connector on the ign switch, or internally in the switch itself.
If you've added some sort of accessories?? like fans, look where they are wired. If you are robbing power off the "dark blue" you may have a problem there.
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Re: Ignition question: voltage from coil.
[Re: Yancy Derringer]
#970000
04/10/11 05:53 PM
04/10/11 05:53 PM
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Joined: Jan 2003
Posts: 815
Alexandria, NJ
WayneM
super stock
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super stock
Joined: Jan 2003
Posts: 815
Alexandria, NJ
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"Sorry I know what you are thinking, but this test is not legit. When you disconnect the ECU, you will have no load on the ignition. You will in fact have an "open ended" harness. Even if the harness had considerable resistance, the meter draws almost no current, and you will show battery voltage OK on both sides. ONLY WAY to check for voltage drop is WITH THE HARNESS UNDER LOAD, as in, "in operatation."" Hey Yancy- You got nothing to be sorry about. I think you're jumping the gun... Circuit integrity comes way after we figure out if everything is wired correctly to begin with. If the ECU was tapped after the ballast, you're only getting 8VDC @ ECU no matter what. I guess you just want to take over? I feel sorry for this guy. This is what's bad about the internet. 
2014 Durango R/T
2004 Dodge Ram 3500 SRW SLT short quad Cummins 6 speed
1998 Dodge Durango SLT 5.2
1971 Plymouth Duster-
<<<<<MOPAR SPOKEN HERE>>>>>
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Re: Ignition question: voltage from coil.
[Re: WayneM]
#970001
04/10/11 08:34 PM
04/10/11 08:34 PM
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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:
"Sorry I know what you are thinking, but this test is not legit. When you disconnect the ECU, you will have no load on the ignition. You will in fact have an "open ended" harness. Even if the harness had considerable resistance, the meter draws almost no current, and you will show battery voltage OK on both sides.
ONLY WAY to check for voltage drop is WITH THE HARNESS UNDER LOAD, as in, "in operatation.""
Hey Yancy- You got nothing to be sorry about. I think you're jumping the gun... Circuit integrity comes way after we figure out if everything is wired correctly to begin with. If the ECU was tapped after the ballast, you're only getting 8VDC @ ECU no matter what. I guess you just want to take over? I feel sorry for this guy. This is what's bad about the internet.
WHAT IN THE 'ELL are you talking about???? If you unhook the ECU, there is no LOAD on the BOTTOM END, the LOAD END of the harness, and you will have NO VOLTAGE DROP across the resistor.
That IS what you said, right? Unhook the ECU and check the voltage?
I feel sorry for you. I've been around electronics since a very young age. I was first licensed as an amateur before I left high school. I spend 6 years in the U.S. Navy maintaining approach RADAR. I've troubleshot automotive electrics, maintained and installed HVAC/R, built some 250 HP dehumidifier dry kilns, and installed and maintained FM radio and telco gear for E911 systems for Motorola.
I have a good idea how the Mopar ECU system is wired and how it works, and I have an unarguable concept of voltage drop across a simple resistor
IT'S CALLED OHM'S LAW and there is a REASON why it is called a LAW.
I'm not trying to deflate your ego, I'm trying to point out that you are incorrect.
So let's go through this ONE MORE TIME
Refer to the diagram:
the below diagram is wiring for a "4 pin" ECU and "2 pin" resistor. The connector is shown "looking in" to the end of it rather than looking "down" on the back
IF YOU REMOVE the ECU connector, and measure the voltage at the Coil positive post AND at the dark blue "ignition run" feeding in, in OTHER WORDS you are measuring AT BOTH ENDS of the resistor, YOU WILL READ EXACTLY THE SAME VOLTAGE WITH THE CONNECTOR REMOVED FROM THE ECU.
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