Exhaust welding

[scottRS4]

Hi, I need to refit the standard exhaust to my Audi RS4. The standard exhaust was modified by means of chopping out the centre section and fitting two straight through pipes.
To refit the original centre section I will need to weld the original back boxes back onto the centre section, and I would want to at least tack them with all parts mounted so that I get the alignment correct.
If I weld them with the parts mounted on the car would disconnecting the battery be sufficient to stop any ecu's getting fried or would I need to do anything else?

[stevieturbo]

It is always reccommended to disconnect the battery before welding.

Although Ive never had any problems welding a car with it still connected.

Just be sure disconnecting wont fk any immobilisers or codes up

[eliot]

Before welding, make sure that you clean the inside of the pipe as much as possible. Otherwise the carbon/soot from inside mixes with your weld and it look like bird poo.

[scottRS4]

Thanks for the advice guys, I will make sure that the pipe is as clean as possible before welding it.

Hopefully I wont wont have any problems with the immobiliser/codes

[oakdale]

Battery disconnection is recommended because of the possibility (which I think unlikely, although not impossible) of damage being caused to the battery and/or the risk of it exploding.

I think there is a much lesser chance of damage to the electronics if the battery is left connected, as it acts as a damper to absorb any spikes in the circuits.

I always leave it connected, but make sure that the ignition is turned off (and key out) for 15 minutes or so before welding, to give the various electronic units time to shut down.

Edited by oakdale on Saturday 5th September 21:47

[Mr2Mike]

The reason the battery should be disconnected has nothing to with it exploding; welding currents can cause significant voltage drops though the bodywork of a car, and if this voltage drop is between two earthing points on a car it can be sufficient to cause equipment to see a reverse polarity or a high voltage spike depending on orientation of the earths and the welding currents. Since the battery ground is the main earthing point, disconnecting it considerably reduces the chance of a problem.

However, this is usually only a problem if your welding ground is a considerable distance from the point you are welding, which is a bad idea anyway. With the welding clamp a close as possible to the welding torch, it's unlikely you'll cause any problems.