This Is Crazy!

KENNHON · January 22, 2010

Go figure! 1996 C-3500 7.4L crew cab dually----- i had replaced inj's and distrib. started it up-runs TERRIBLY----and when i turned off key---it kept running!!!!!!!!!!![i know a FEW reasons why this would happen!]... BUT when i removed the negative cable---it STILL kept running!!! HOW CAN THIS BE????????????

brims · January 22, 2010

You have an alternator that kept it going. Also I believe that's bad for the electrical system.

rmck490 · January 22, 2010

Go figure! 1996 C-3500 7.4L crew cab dually----- i had replaced inj's and distrib. started it up-runs TERRIBLY----and when i turned off key---it kept running!!!!!!!!!!![i know a FEW reasons why this would happen!]... BUT when i removed the negative cable---it STILL kept running!!! HOW CAN THIS BE????????????

I believe it means your alternator is working correctly. You only need the battery to start the vehicle and keep things alive when you turn off the ignition (like radio clock and PCM). After the vehicle starts, the alternator provides all the current needed for most everything and charges the battery. This is one way you can check the alternator by removing the neg cable. If the car dies, your alternator or voltage regulator could be bad.

nfisherman · January 22, 2010

I was always told that you should never remove a battery cable while engine is running because it can ruin the alternator. Is that true?

orlan85 · January 22, 2010

Go figure! 1996 C-3500 7.4L crew cab dually----- i had replaced inj's and distrib. started it up-runs TERRIBLY----and when i turned off key---it kept running!!!!!!!!!!![i know a FEW reasons why this would happen!]... BUT when i removed the negative cable---it STILL kept running!!! HOW CAN THIS BE????????????

I believe it means your alternator is working correctly. You only need the battery to start the vehicle and keep things alive when you turn off the ignition (like radio clock and PCM). After the vehicle starts, the alternator provides all the current needed for most everything and charges the battery. This is one way you can check the alternator by removing the neg cable. If the car dies, your alternator or voltage regulator could be bad.

+1

Thurman · January 22, 2010

The issue seemed to be that the owner stated his truck kept running even when he turned the key OFF. THAT is not normal. This sounds as if you may have a bad ignition switch, or maybe some wiring got mixed up when you did all of the work. On a 1996 model it would run IF the negative battery cable would be disconnected from the battery while the engine was running. As stated, the '96 model used the battery to crank the motor and for accessories, then the alternator basically ran the electrics of the motor. Hopefully you have gotten the motor to shut down, and figured out your problem by now. David

grose67 · January 22, 2010

I was always told that you should never remove a battery cable while engine is running because it can ruin the alternator. Is that true?

It is not something you should do multiple times a day, but every once in awhile wont kill anything. It is a sure fire method of checking the alternator. As far as the motor continuing to run after the ignition being shut off, that sounds like a wire or switch problem.

brims · January 22, 2010

I was always told that you should never remove a battery cable while engine is running because it can ruin the alternator. Is that true?

It is not something you should do multiple times a day, but every once in awhile wont kill anything. It is a sure fire method of checking the alternator. As far as the motor continuing to run after the ignition being shut off, that sounds like a wire or switch problem.

A volt meter will tell you the same thing, and won't introduce dangerous spikes into the electrical system. The battery voltage will be under 12.6 I believe it is if it's not charging.

music · January 22, 2010

IIRC, the battery is part of the regulator circuit for the alternator, so disconnecting it can cause the alternator to not regulate voltage correctly (i.e., it will increase current output to compensate for a sudden drop in the normally steady "load" presented by the battery). I personally would not do that as a test, especially with all the computers we have now. The computers will have have a separate voltage regulator (probably 5V), but they have their limits for input too.

KENNHON · January 22, 2010

IIRC, the battery is part of the regulator circuit for the alternator, so disconnecting it can cause the alternator to not regulate voltage correctly (i.e., it will increase current output to compensate for a sudden drop in the normally steady "load" presented by the battery). I personally would not do that as a test, especially with all the computers we have now. The computers will have have a separate voltage regulator (probably 5V), but they have their limits for input too.

Thanks.... As you saw, i said AFTER i shut off key-itstill kept running.... my ign sw. was fine when i took this garbage apart 2 months ago.... don'thave a clue as to why....i'll haveta trace wiring and other crap... VERY hard to time correctly[computer is not compensating

Zembonez · January 22, 2010

I was always told that you should never remove a battery cable while engine is running because it can ruin the alternator. Is that true?

This can cause damage to the alternator. Any voltage surge when the cable is disconnected (or reconnected) has nowhere to go and can damage the built in voltage regulator. Key word here is CAN.

KENNHON · January 24, 2010

I was always told that you should never remove a battery cable while engine is running because it can ruin the alternator. Is that true?

This can cause damage to the alternator. Any voltage surge when the cable is disconnected (or reconnected) has nowhere to go and can damage the built in voltage regulator. Key word here is CAN.

I called an electrician that knows auto's,too. Robert and this pervious chap are CORRECT! do not take off neg. terminal while running with 'load' on elec.system--As Robert said it CAN cause damage. My buddy also came up with the 'why and wherefore' of my problem. What i didn't mention ws ---i have a remote start/alarm sys.[Cobra]... and there is a ground on the alternator so if someone cuts your cables, there still is power for alarm and remote start function.... ONLY thing left to do is TAKE OUT distributor[this is a B**** on a '96 BB!] and advance distributor[computer is NOT compensating for late timing enuff! THANKS to ALL who took the time to respond!

az'03Silverado · January 24, 2010

I work for a flight school and one morning I was using our '89 GMC (pos) to jump start a Piper Warrior. I got the jumpers all hooked up and with the truck running I went to crank over the airplane. It was such a draw on the truck's battery that the truck's engine died. Needless to say, not only was the airplane's battery dead, but the truck's battery was crap.