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Welding in a vehicle with a computer

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RobMD

12-18-2007 06:02:37




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I was told that all you had to do in order to weld floorpans on a later vehicle with a computer is remove the negative ground cable.

However, after welding, the truck runs erratic, hesitates and stuff with no check engine light. Have I fried the computer?




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david b. guest

12-19-2007 21:29:17




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 Re: Welding in a vehicle with a computer in reply to RobMD, 12-18-2007 06:02:37  
RobM, Rustyfarmall took the words outta my mouth exactly! Disconnect battery and you lose driveability which will return after 4 or 5 days of normal driving and relearning program.



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RobMD

12-18-2007 14:10:21




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 well, that was rather...ODD in reply to RobMD, 12-18-2007 06:02:37  
I disconnected the battery in a last minute haste and touched the two cables together, turned the key switch off and on about 5 times, and then drove it right up the highway.

No more problems, thank heavens. It's a 95 f150



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02XLT4X4

12-18-2007 11:53:42




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 Re: Welding in a vehicle with a computer in reply to jdemaris, 12-18-2007 06:02:37  

fepo69 said: (quoted from post at 09:28:43 12/18/07) I'm with stumpalump on this one, as an electrical engineer I also can tell you it is not good to remove ground from circuit boards, if you do you leave ground side floating and no place for stray currents to go but back into the device.


But if you are welding with the vehicle turned off then electricity isn't flowing to the ground anyway, it is going backwards from what is normally the chassis ground to the + side of the battery. I pull off both cables just to be safe and haven't had any issues, but my old truck is about as complex as a hammer, I just do it for the sake of my CD player.

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Weldin man

12-18-2007 08:24:05




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 Re: Welding in a vehicle with a computer in reply to RobMD, 12-18-2007 06:02:37  
On all Fords after 2005 with power stroke diesels you have to remove the Computer- ABS computer and the entire instrument cluster to weld on them.Cat -Cummins and most others say to unhook the wiring harness at the computer. Most of the older ones you can get by with unhooking the battery cables , but be very careful where you hook your ground cable,keep it as close to where you are welding as possible, don't hook it to the frame and weld on the chassis or the chassis and weld in the frame.

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Mike M

12-18-2007 10:40:58




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 Re: Welding in a vehicle with a computer in reply to Weldin man, 12-18-2007 08:24:05  
Our problem truck had a gas engine. And I think you are right by having to unhook everything !



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Stumpalump

12-18-2007 08:20:32




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 Re: Welding in a vehicle with a computer in reply to RobMD, 12-18-2007 06:02:37  
I'm with Rusty on giving it a chance to re learn. The last one I fooled with I touched the disconected battery leads together and turned the key on for 30 seconds to reset the computer. It fixed it.1998 Jeep Cherokee. As far as disconecting the battery before welding I thing your all wrong. Leave it hooked up with the key off and you will be OK. You blew the computer because it had no ground. Correct me if im wrong. I fix expensive medical devices for a living and the computer boards cost as much as a good used truck. I leave the instrument pluged into the wall and turn it off before I touch anything inside. The cord has the ground and if you touch stuff inside without it all being grounded than static will take out the boards. Sounds crazy but "belive it or not". I also ground myself to the instrument wich in turn is grounded to earth.

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CH(upstate,NY)

12-18-2007 13:45:24




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 Stumpalump, sounds like we have something.. in reply to Stumpalump, 12-18-2007 08:20:32  
In common. Except the Med equipment is 480 3ph. Single point ground to all subassemblies and magnet(hint hint).



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fepo69

12-18-2007 08:28:43




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 Re: Welding in a vehicle with a computer in reply to Stumpalump, 12-18-2007 08:20:32  
I'm with stumpalump on this one, as an electrical engineer I also can tell you it is not good to remove ground from circuit boards, if you do you leave ground side floating and no place for stray currents to go but back into the device.

I welded the exhaust on my Sentra with a Mig, made damn sure the ground lead of Mig was connected close by to weld area and that it was clamped to a cleaned area of metal for positive connection.

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s.crum

12-18-2007 08:18:45




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 Re: Welding in a vehicle with a computer in reply to RobMD, 12-18-2007 06:02:37  
I've always had the policy of un-plugging all computer modules in a vehicle before any arc work is done (welding, plasma etc). Several years back an area fire company wanted some welding done on an overflow drain on one of their tankers. This was an extension tube and all stainless and not removable from the truck. Since all I use on stainless is high frequency TIG, I insisted that they send someone with the truck to disconnect all electronics in the truck. The chief found this unacceptable and would only agree to disconnect the battery cables, so I turned the job down. About 6 months later I was told by a member of the fire company that they found somebody else to do the job. After about 30 minutes worth of welding, the truck had to be wreckered down state to a dealer to have a "couple electric issues" ironed out to the tune of 3 weeks down time and several thousand dollars.
I heard of one instance of a guy stiking an arc on a trailer hitch on a late 90s GM car and the airbags blowing.
So I would consult a dealer before I did any welding on anything with computers unless you disconnect the computers BY THE BOOK. Yes there are correct ways to do this to avoid damaging the computers or touching off the air bags. Things are a lot more complicated than they used to be.

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JT

12-18-2007 08:10:57




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 Re: Welding in a vehicle with a computer in reply to RobMD, 12-18-2007 06:02:37  
you can take it to Auto Zone, O'reily's, Advnace Auto and they normally have a cheap scanner to hook up and see if there are any codes in it. You might also unhook the positve battery cable let it set for 5 minutes and this will clear any codes in older systems if there are any fault codes.



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glennster

12-18-2007 08:03:20




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 Re: Welding in a vehicle with a computer in reply to RobMD, 12-18-2007 06:02:37  
yup, if its got a puter, disconnect the ground from the battery. the surge from the welder can do a lot of damage to the electronics. there is an adapter that will take a 9volt battery (the little square one for smoke alarms and such) you plg the battery into the adapter and put it in the cigarette lighter socket on the vehicle. it will keep a small amount of juice to the ecm to retain the memory. if not you need to drive the car so it relearns the settings. be careful of honda's with factory anti theft radios!!! if you disconnect the battery, it locks the radio out, you need a special code to unlock the radio, after 10 trys it shuts the radio down for good !!! (the radio will have a blinking light when the car is shut off on the radio face)

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El Toro

12-18-2007 06:44:28




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 Re: Welding in a vehicle with a computer in reply to RobMD, 12-18-2007 06:02:37  
You may need to take it to a shop and see if any fault codes are present. A man had his Nissan
Magnum detailed and they used some kind a solution to clean the carpets and it wouldn't start when they finished. The owner had the car towed to the Nissan dealer that was less than a mile away and they told the owner it was the computer. I don't know if the owner was reimbursed by the detail owner. Hal

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Dave from MN

12-18-2007 06:26:17




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 Re: Welding in a vehicle with a computer in reply to RobMD, 12-18-2007 06:02:37  
Call closest dealer for each brand and ask them, model and year specific, what you should do, ask to speak to the tech with the most electrical knowledge. Even the best shops have knuckle heads.



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Mike M

12-18-2007 06:14:41




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 Re: Welding in a vehicle with a computer in reply to RobMD, 12-18-2007 06:02:37  
What make and year of truck ? Our body shop just had an 2005 Ford in here and they swear they unhooked the cable before welding on it. Well we had to take it to the Frod dealer and $3,500 later it was all fixed. New instrument cluster,wiring harness,and some modules. I wish I knew for sure what happened in order to prevent it from happening again !



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RustyFarmall

12-18-2007 06:12:50




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 Re: Welding in a vehicle with a computer in reply to RobMD, 12-18-2007 06:02:37  
I'm certainly no expert, but I think some of the older systems would actually lose their memory when the battery was disconnected, and had to be run and driven for awhile after to give the computer a chance to re-learn.



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