Electrical system draw Draw
Thread Starter
Staging Lane
Joined: Nov 2006
Posts: 86
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From: B.C. Canada
Electrical system draw Draw Hi Fellas, I have a '65 Corvette with an LQ9 correctly installed. Has all sensors except rear O2s. Has functional ALDL. My batt goes to 8v after a couple days while connected to car. Stays at 13.2ish for the first 3 days and the suddenly 8v/No start. Took batt in for full slow charge and load test - tested OK.
Shows 12.2v draw between batt+ and +cable. Won't light test lite between batt+ and and +cable. Pulled all fuses and disconnected alt. Still shows draw.
Disconnected ECM - no draw.
Then connect alt - 11.6v draw. Then re-connect ECM - back to 12.2v draw.
2 days now with batt disconnected, batt still at 13.2v. Any ideas what may be a problem?
Thanks, Frank
Shows 12.2v draw between batt+ and +cable. Won't light test lite between batt+ and and +cable. Pulled all fuses and disconnected alt. Still shows draw.
Disconnected ECM - no draw.
Then connect alt - 11.6v draw. Then re-connect ECM - back to 12.2v draw.
2 days now with batt disconnected, batt still at 13.2v. Any ideas what may be a problem?
Thanks, Frank
TECH Addict
Joined: Jun 2009
Posts: 2,012
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From: Tulsa, OK
If you're showing a draw through the alternator, it's wired wrong. That would be the field flash, and it's supposed to be switched. In other words, you shouldn't see that with the key off, only key on.
If you show a draw with all fuses pulled, you have a short circuit somewhere between the battery and the fuse box.
If you show a draw with all fuses pulled, you have a short circuit somewhere between the battery and the fuse box.
Thread Starter
Staging Lane
Joined: Nov 2006
Posts: 86
Likes: 0
From: B.C. Canada
Thanks for taking the time to respond fleetmgr. I should have mentioned, the car has been in use regularly for 5 years in this configuration. It will sit for several months in the off season and start up as it should...
The discharge is a new condition.
The alt is not stand alone - it still runs thru the ECM.
The discharge is a new condition.
The alt is not stand alone - it still runs thru the ECM.
TECH Addict
Joined: Jun 2009
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From: Tulsa, OK
In spite of it being in this configuration for some time, you still have something that has changed. The one and only way to get a draw with all fuses removed is to have something that has via some mechanism shorted out. And said short can only be between the fuse box and the battery, this assumes that ALL power is routed through the fuse box as it should be. If something is routed outside the fuse box, then all bets are off.
If the engine is off, there should be no power through the alternator. You will show 12v at the hot stud, but the rest should be at 0v. If you see anything besides the 12v at the hot stud, something is wrong....and it doesn't matter what is controlling the alternator...something is wrong. As I stated, 12v to flash the field, which is the only other thing that would normally be present, should be switched so that it is off when the key is off.
If the engine is off, there should be no power through the alternator. You will show 12v at the hot stud, but the rest should be at 0v. If you see anything besides the 12v at the hot stud, something is wrong....and it doesn't matter what is controlling the alternator...something is wrong. As I stated, 12v to flash the field, which is the only other thing that would normally be present, should be switched so that it is off when the key is off.
Thread Starter
Staging Lane
Joined: Nov 2006
Posts: 86
Likes: 0
From: B.C. Canada
Thanks again fleetmgr.
More specific numbers. I'm gettin' out of my league here.
Alt and ECM disconnected 0v draw
Alt only connected 11.0v draw
Ecm only connected 11.7v draw
Both connected 11.7v draw
Alt only connected .04Ma draw
Ecm only connected .15Ma draw
Both connected .20Ma draw
The Ma draw seem low but there is voltage ... WTF?
3 days and the batt is still at 13.15v
Any thoughts anyone?
More specific numbers. I'm gettin' out of my league here.
Alt and ECM disconnected 0v draw
Alt only connected 11.0v draw
Ecm only connected 11.7v draw
Both connected 11.7v draw
Alt only connected .04Ma draw
Ecm only connected .15Ma draw
Both connected .20Ma draw
The Ma draw seem low but there is voltage ... WTF?
3 days and the batt is still at 13.15v
Any thoughts anyone?
Last edited by 00fxd; Aug 29, 2014 at 11:04 PM.
you keep saying voltage is drawn. it is current that is drawn, not voltage.
so when your alternator and ECM is not connected, naturally there will be no voltage... because the wires are disconnected. when you connect the wires, then you will either measure voltage present at the device or you won't, will depend on what you're measuring and what it's function is.
where you mentioned .04Ma, .15Ma, .20Ma draw. you are saying less than a milliamp... 40 microamps, 150 and 200 microamps. was that correct?
and initially you said battery disconnected for 2 days and it's at 13.2 volts, i find that hard to believe. no car battery will sit higher than 12.7 to 12.8 volts, unless you have a charger on it. so if that was the case what make/model meter are you using?
and what make/model alternator? besides the large output wire to it, how many wires does it have plugged in to it? and how is it wired to your ECM?
so when your alternator and ECM is not connected, naturally there will be no voltage... because the wires are disconnected. when you connect the wires, then you will either measure voltage present at the device or you won't, will depend on what you're measuring and what it's function is.
where you mentioned .04Ma, .15Ma, .20Ma draw. you are saying less than a milliamp... 40 microamps, 150 and 200 microamps. was that correct?
and initially you said battery disconnected for 2 days and it's at 13.2 volts, i find that hard to believe. no car battery will sit higher than 12.7 to 12.8 volts, unless you have a charger on it. so if that was the case what make/model meter are you using?
and what make/model alternator? besides the large output wire to it, how many wires does it have plugged in to it? and how is it wired to your ECM?
Thread Starter
Staging Lane
Joined: Nov 2006
Posts: 86
Likes: 0
From: B.C. Canada
Thank you FMF. You are correct of course, current is drawn.. I don't often deal with these issues so I am a bit out of my league.. The alt is the original 'Dephi' alt and is wired as it would have been originally to the ecm in a 2004 LQ9 - blue wire disconnected gray and brown connected.
The gauge is a "Micronta" digital, Radio shack unit. There was no charger on the batt during the 'test' period that the batt was disconnected.
I drove the car two days ago on a 450mi. road trip. When I shut it down I forgot the headlites on for a 1/2 hour or so. 12.96v at this time after 2 days.. not disconnected from car.
The gauge is a "Micronta" digital, Radio shack unit. There was no charger on the batt during the 'test' period that the batt was disconnected.
I drove the car two days ago on a 450mi. road trip. When I shut it down I forgot the headlites on for a 1/2 hour or so. 12.96v at this time after 2 days.. not disconnected from car.
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i can only tell you what i know, on my 2002 camaro it has 1 wire to the 4-pin plug and the pcm puts 5v on it, it is known as the exciter wire and in gm speak the generator turn on signal. the voltage regulator sees that 5v and then makes the alt. output power. the internal voltage regulator handles everything and maintains ~14 volts output under all conditions. if the voltage regulator fails or the alternator has a problem, that pin gets connected to ground in the alternator, the pcm sees this connection to ground and is how the pcm knows the alternator is in a failed state.
later model years started using more wires and got more sophisticated, a way to gain more fuel economy is to make the alternator output less voltage (less parasitic load on engine) and it did that with a wire to the voltage regulator for field duty cycle, the pcm would put a PWM signal on there to control alternator output. i don't know what your gray, brown, blue wires actually do but that'd be my guess among other things. if you have those connected wrong then wouldn't surprise me if you have enough of a current draw when engine off to drain battery. how you got by 5 years with it like this... i dunno. did you drive it frequently?
your using the ecm/pcm out of a 2004 gm vehicle that had this LQ9 in it?
later model years started using more wires and got more sophisticated, a way to gain more fuel economy is to make the alternator output less voltage (less parasitic load on engine) and it did that with a wire to the voltage regulator for field duty cycle, the pcm would put a PWM signal on there to control alternator output. i don't know what your gray, brown, blue wires actually do but that'd be my guess among other things. if you have those connected wrong then wouldn't surprise me if you have enough of a current draw when engine off to drain battery. how you got by 5 years with it like this... i dunno. did you drive it frequently?
your using the ecm/pcm out of a 2004 gm vehicle that had this LQ9 in it?
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Staging Lane
Joined: Nov 2006
Posts: 86
Likes: 0
From: B.C. Canada
I drive the car a lot considering that I work at home. Several thousand miles each year for the past 5 years. I do not have a charging problem, I had evidence that I have a drawing down the battery problem when the car sits. I am quite sure that I do not have any connections wired wrong, and I am using the correct PCM for the engine.
I may have fixed whatever was causing the condition with my going thru the systems lately and checking connections. 3 days now, batt connected, 12.91v. I think all is well now... Thanks...
I may have fixed whatever was causing the condition with my going thru the systems lately and checking connections. 3 days now, batt connected, 12.91v. I think all is well now... Thanks...