964 front pan welding - what about electronic damage?

[hemeoncdoc]

I have a 1990 964 C4 that needs replacement of the forward aspect of the front trunk floor. The pan just behind the front bumper cover got scraped leading to rust perforation there. I have the replacement part, and will use the forward part of it and MIG weld it in place. However, I have only welded on a SWB which had no electronics of concern. I have read various recommendations from removing EVERY electronic part in the car, to just make sure the grounding cable is placed close to the weld and on to well-cleaned steel for a good connection.

I dont want to fry the electronics. What should I do?
Thanks in advance!

[David McLaughlin]

Buy a surge protector. Attaching it to the battery curcuit will most likely protect the car.

[962porsche]

all you have to do is disconnect the battery .
in your case you should be removing it to do the job .
I have been doing welding on cars for well over 30 years now and I have only seen one time were the cars computer was damaged .
and it was totally the falt of the tech that was working on the car .
he was welding with the battery hooked up and next to the air bag sensor a hot spark landed on the two wires at the sensor and grounded the two wires and set off the air bags in the car . though with that is was not the computer it was still damage from welding . the time it damaged a computer was pretty much the same thing . the battery was not hooked up and the tech was repairing a rust hole over the computer on a 944's battery tray he pulled back the carpet but left the wiring and ecu and did not cover the ecu with a fire blanket and a hot weld dropped onto the wiring right at the ecu and burned /melted right thru some of the wiring . when the tech went to start the car after he was finished the car was totally dead .

the real chance that you will damage the cars computer from welding is quight small . if your really going to worry about it just unplug the computer .

[mreid]

The only electronics I've ever damaged when welding on a car was an MSD box. It happened twice and disconnecting the battery didn't help. You have to disconnect and isolate both the heavy red and heavy black wires. All other cars, no problems.

[hemeoncdoc]

Thanks for the advice! Makes my job a lot easier. Once again, this forum is excellent!

[911MD]

Can you please let know where did you get the floor panel replacement part I have the same rust issue

[hemeoncdoc]

Sorry for the late reply. I just saw your question. I got the pan and battery bracket from Sunset Porsche. A few pointers: the pan is "weld-bonded" along the front and sides with epoxy panel adhesive and spot welds thru that. I used the SEM structural metal to metal panel adhesive. The battery bracket is spot-welded to the pan (sold as separate parts). There are a few studs that are welded to the pan also (that don't come on the pan), such as one under the ABS on the driver's side, and 2 for the metal strip that covers the battery cables. I cut across the back of the trunk and seam welded with the MIG. Not fun, but use several sheet metal clamps to keep it flat. I used the 3M Body Schutz to coat the trunk and underside. Mask off what you dont want to deal with repainting later, and body schutz any area that you will paint over (likely all of the body schutz). The Porsche trunk paint and undercoating cannot be repainted, at least without applying epoxy primer, it seems, to avoid a perpetually tacky surface that will not harden. So my advice is to mask it, spray what is visible with the body schutz, then prime and paint over that, no problem. The photos show the before and after...