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Topic Review (Newest First)
11-24-2005 02:18 PM
MARTINSR ICAR guidelines say don't weld within 18 inches of a computer. Just disconnect the battery and the 18 inches is all that is needed. It also suggests don't allow your feed line, ground cable or power supply cord to be in a circle, this could produce an electro magnet effect.

11-24-2005 02:14 PM
oldred Fiurbird, You are right, definitely disconnect the battery. I did not mean to make it sound as if disconnecting the battery is a waste of time but all too often someone will think they can just do about anything they want with the welder without harm because the battery is disconnected so it will be safe. One still needs to exercise caution when welding on any vehicle, computer or not. It really is simple just look at where the welding will take place vs WORK clamp and ask "what will the current travel through in this configuration"? If welding on a door and clamped to THAT door then that is all that will be affected but if clamped to the frame and welding on the door then every thing capable of carrying current between body and frame will share the load plus the door hinges also
11-24-2005 11:11 AM
Originally Posted by milo
If you let the smoke out of some computers it'll kill em.
I've noticed that to be true with most electronics. LOL!
11-24-2005 10:50 AM
firebird_red Yes, the work clamp is not grounded to anything. It is deliberately "floating" so that the flow of current is from the electrode back to the welder without going through any other paths.

I would definately disconnect the battery before welding. Electromagnetic fields are created by welding that could alter the computer programming even if it doesn't zap the circuits. Just as you hear the welding electromagnetic interference on radios nearby, these signals are present on the input leads to the engine computer when you are welding. The memory is more likely to be altered with the 12V power applied. I think it's also good idea to remove the computer AFTER the battery is disconnected, just because they are so expensive.

The "keep alive" gadgets keep the computer powered up. They don't serve a purpose in this application because you really want power to the engine computer memory off so it doesn't get accidentally programmed (altered). The keep alive device is effectively a small power source that maintains 12V on the system but it doesn't have enough current available to harm you if a wrench gets across it.
11-23-2005 07:54 PM
oldred Kringold, Good point!
11-23-2005 07:42 PM
kringold There is no such thing as a ground clamp or ground lead. It is a work clamp/lead. It does not ground the circuit, but completes the circuit.
11-23-2005 07:38 AM
oldred The problem is that body to frame grounds are not designed to carry a weld load of over a 100 amps or even more, or at least I think this is the case.
11-22-2005 10:20 PM
milo There is a do-hicky from Matco Tools that can help protect also. The idea is you won't have to reset clocks and radio stations etc. by hooking to the battery during welding operations.

If you let the smoke out of some computers it'll kill em.
11-22-2005 05:48 PM
oldred Firebird, I think the same thing, I just can't see how unhooking the battery will help all that much but it seems that a lot of people say just unhook the battery and it will be ok. I think not.
11-22-2005 03:18 PM
firebird_red The key is correct placement of the ground clamp. If you run welding current from the exhaust pipe, through the engine back to various ground connections, it won't help much that you disconnected the battery. The ground needs to be next to the welding so the current flow path isn't through the engine electronics.
11-22-2005 10:14 AM
Originally Posted by redlightning
,and all he did was some welding on the exhaust system.

key phrase right there

all my exhaust welds are done with a 90* bracket and a hose clamp that when on the pipe, give me a handy place to connect the ground to the pipe

ive seen MANY MANY techs slap the ground on the frame while welding a new exhaist tip or muffler on .... pretty easy for power to travel up the ehaust (because chances are its rubber mounted) and into the ECU through a coolant sensor or something

incredibly rare, but possible

i dont see how disconnecting the battery raly makes a difference tho, all your doing is decucing the # of possible power supplies from 2 to one ...
11-22-2005 09:41 AM
bluesman123 All sounds like good advice. On my truck it is so easy to disconnect the battery AND the VCM that I would do it anyway.

Welded hinge pins?? That must have been a shock!

11-21-2005 07:58 PM
MARTINSR I'm with you Carl, I don't doubt for a second you can't smoke something, but I think you have to go out of your way to do it. I mean, you have to want to do it.

I use a "surge protector" when ever I weld on any computer controled car. Or unhook the battery of course. Even if it is a CYA thing, so is wearing seat belts and I do that everyday as well.

11-21-2005 04:43 PM
redlightning I am a honda mechanic.They ask me to go to a body shop down the road and program a key for them on an accord.I took our scan tool and programmed the key and it would not start.I ask him did it start before.He said yes ,and all he did was some welding on the exhaust system.They towed it to the dealership and I found no output from pcm.I installed a known good pcm and then got a map code and found the map sensor open.I replaced both of them it ran fine.To take both those out.I really wondered if he didn,t have the key on maybe listening to the radio or something.
Brian,I lurk around the body forum often.I am not questioning your knowledge or experience.This one might have been one in a million that got zapped. I don,t know these guys so I don,t know what else they did.
11-21-2005 11:17 AM
MARTINSR Unless you hook the ground cable to the alternator I can not imagine anything happening, another "old husbands tale".

I do know that with late model computer controled cars, you should always disconnect the battery. But honestly, it is a CYA deal, I have NEVER seen any kind of damage what so ever concerning this.

I have however seen exactly what Oldred is talking about. I have seen hinge pins welded because the guy gounded the body and welded on the door. I have seen a throttle cable burn right in half because he grounded the exhaust and welded on the body! Put your ground as close as you can to the weld and ON THE SAME PART.

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