Will the engine remain running,
06-01-2022, 11:30 PM
#2
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Year: 1989
Model: Comanche (MJ)
Engine: 4.0
DO NOT DISCONNECT THE BATTERY WITH THE ENGINE RUNNING. That's an old redneck trick to check the alternator, but a great way to damage the electronics on a modern car.
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06-02-2022, 09:56 AM
#3
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The battery is part of the system, expected to be there. In some systems it is a required load. If removed, it may cause voltage spikes which can damage things. Id not try that test, do Not try it.
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doublechaz (06-03-2022)
06-02-2022, 10:20 AM
#4
Senior Member
Possible, but probably not. Most modern vehicles won't, but as stated it is very possible to fry stuff without the battery there to act as a voltage damper.
06-02-2022, 10:31 PM
#5
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There was a small bump in voltage +16VDC but the engine remained running for the short moment we pulled the cable..
My point that if the battery goes open while running, the engine will not quit. Im guessing now that the ASD circuit wont drop off either.
My point that if the battery goes open while running, the engine will not quit. Im guessing now that the ASD circuit wont drop off either.
Last edited by MtnGoat; 06-03-2022 at 12:10 AM.
06-02-2022, 11:16 PM
#6
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Year: 1989
Model: Comanche (MJ)
Engine: 4.0
The generator puts out pretty big voltage spikes without the battery to smooth it out. That 16-volts was just the average of the nastiness.
For the record, if you try that with an older Ford that has an EEC-IV ecm, it'll run for about a minute before it lets the smoke out. Been there and watched that happen when they tested the emergency cutoff switch on a race car. It really didn't like the 30-volt spikes from the alternator, which is supposed to get wired on the battery side of the kill switch.
For the record, if you try that with an older Ford that has an EEC-IV ecm, it'll run for about a minute before it lets the smoke out. Been there and watched that happen when they tested the emergency cutoff switch on a race car. It really didn't like the 30-volt spikes from the alternator, which is supposed to get wired on the battery side of the kill switch.
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06-03-2022, 12:40 PM
#9
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06-03-2022, 02:48 PM
#10
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Just because you did it doesn't make it a good idea.
As a general rule of thumb, unplugging things that are powered up is a huge no-no...not just because it might fry your electronics, it might fry you. There's better ways to see if circuits are energized or have continuity. Basic electrical troubleshooting and a simple meter is much safer than handling an energized circuit.
As a general rule of thumb, unplugging things that are powered up is a huge no-no...not just because it might fry your electronics, it might fry you. There's better ways to see if circuits are energized or have continuity. Basic electrical troubleshooting and a simple meter is much safer than handling an energized circuit.
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06-03-2022, 07:50 PM
#11
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06-04-2022, 01:07 AM
#13
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