I've got Tuesday off work again, and have decided that I'll go by a friend who has an arc welder and get one annoying noise removed from my car.

There is a cracked weld to the rear of that perforated heat shield thing that goes over the catalytic converter, and during acceleration, or whilst idling (which is not the smoothest), there is an annoying metallic noise. If I get under the car whilst the rattling is going on, I can press directly against the cracked weld and the noise stops, so I'm fairly sure of my diagnosis.

What precautions do I need to take, to avoid the arc welding process frying some of my car electronics ? I'm assuming that my friend will clamp his welding lead somewhere on the exhaust close by the area being worked on, so the current flow should be in a fairly self contained loop in the exhaust shouldn't it ?

Aside from maybe disconnecting the car battery (?), is there anything else I could / should do ?

John Marshall
1994 940GL wagon
Christchurch NZ

I think I would feel OK about leaving things connected if the current is local to the exhaust system, EXCEPT for the O2 sensors. I would unplug them and make sure the plugs are fully isolated from possible contact with any metal.

Have him bring the welding cables into the exhaust straight on and don't loop them anywhere where the loop of welding cable could run parallel to any wires in the car. With this precaution you should be OK.
--
'96 965 with 16' wheels at 119K. Had '85 745 Turbo Diesel for 200K.

In addition to Spook's notes, you might disconnect the air bag sensor, which is quite sensitive to stray voltages and very expensive to replace. It's located under the seat, if your car is so equipped.

Dear Steve,

Good a.m. The SRS sensor is the airbag sensor. I should have been clearer.

Yours faithfully,

spook

Dear John,

May this find you well. Definitely - DEFINITELY - disconnect the negative battery cable clamp from the battery, and put the clamp in a plastic bag (to ensure that it remains isolated).

As a further precaution, I'd disconnect the ECU from its connector. Wait for 10 minutes, after disconnecting the negative battery cable clamp, before removing the ECU connector. The ECU can be left in place, behind the kick panel on the door-side of the driver's side foot-well (passenger side, in a US vehicle).

It might be well do this for the SRS sensor. However, that will require removal of a seat. On US/Canadian cars, the sensor is under the driver's seat (on the right, as one faces the bonnet). I do not know if on NZ/UK/Japan vehicles, the sensor is there, or on the other side. If you elect to do this, first remove the negative battery cable clamp, as mentioned above.

So far as I know, there are no other sensitive/costly electronic components, which need to be protected.

Re-install electronic components before re-connecting the negative battery cable clamp. The radio code will be needed to re-activate the radio.

Hope this helps.

Yours faithfully,

spook