Exhaust Welding

[MG David]

When welding on older cars (dizzy and carbs) I disconect the battery and pull the plug out of the altenator. However I now need to weld a new bend into the exhaust on one of our more modern cars with an engine management system. Will disconecting the battery and altenator be sufficient?

 

[boydy1989]

if you connect the earth clamp to the exhaust near by i can't see it causing any problem.

I still havn't had a reasonable explanation as to why welding to a car which is all still connected causes problems, can anyone enlighten me?

assuming, of course, you have a good, clean path to earth through the clamp.

 

[john224]

If ive got this right on cars with ((ECUs)) when you weld on a car which is still connected to the battery you stand a chance of spiking the ECU as when you strike the arc weather mig or arc you are actually doing a direct short which can blow the ECU and the alternater,,think this is correct if not some one else will correct me,,,john

 

[NTwoO]

I've always just flailed away after connecting the earth clamp as close as possible to the weld. The way the currents flow should not cause any spikes in your circuits, unless your torch and earth leads form a huge loop that could emit a pulse. This can be compensated by twisting the two to make a smaller loop.

 

[clueless77]

welded an outrigger on my landy on sunday and forgot to disconnect the battery, only realised when i finished welding. put the keys in and it started first time. next time i'll disconnect the battery in case i was just lucky.

 

[boydy1989]

ive welded my landy many times, i also welded my injecteed metro the other day and it started jus fine after.

whilst i can understand how welding with the ecdu in circuit, i.e. using the casing of it as an earth point, would damage it, the welding current will travel from the weld, along the panel to the earth point. How can it 'spike' the ecu?

If it is an inducted current that is of concern, surely the 30-40,000 volts ignition system will generate more interference and induced noise?

 

[cortina2003]

hi
on any car,,take off the battery,,,i have seen a battery explode!!! and wow,,,very huge bang and flames,,,car was total right off!!! we live and learn
but it is a must to remove the battery,even just disconnect it

 

[shenion]

whilst i can understand how welding with the ecdu in circuit, i.e. using the casing of it as an earth point, would damage it, the welding current will travel from the weld, along the panel to the earth point. How can it 'spike' the ecu?

Suppose you're welding an exhaust. Under the car you use those nice big lugs on the transmission for the ground clamp. Weld exhaust and zap the ECU.

The only electrical connection to the engine ground is through a rusty set of flange bolts and a fiber donut. So the exhaust develops a considerable voltage relative to the engine/tranny.

The ECU has a connection to the oxy sensor on the exhaust. Since the exhaust is spiking up, it arcs through the oxy sensor then through the ECU.

Same for drive train; have seen rear ends cause radio issues as they can become completely isolated. Usually no heavy ground to them. Weld suspension and have the ground on a different part and current flows back through the ABS sensors to the ECU.

Keep the work lead close and on teh same part your are welding. I never disconnect the battery but do unplug oxy sensors when welding an exhaust.

 

[MG David]

Thanks for your comments.
It sounds then that if I put the earth clamp on a clean part of the exhaust close to the weld there should not be a problem. However, disconnecting the battery and the A/F ratio sensor would not be a bad idea just to be on the safe side.

 

[boydy1989]

Suppose you're welding an exhaust. Under the car you use those nice big lugs on the transmission for the ground clamp. Weld exhaust and zap the ECU.

The only electrical connection to the engine ground is through a rusty set of flange bolts and a fiber donut. So the exhaust develops a considerable voltage relative to the engine/tranny.

The ECU has a connection to the oxy sensor on the exhaust. Since the exhaust is spiking up, it arcs through the oxy sensor then through the ECU.
.

this makes perfect sense, but again it seems a case of a poor choice of earth point, which in turn, for an easier/stronger weld, makes sense to pick a better earth rather than just disconnect bits of the car. surely?

I know of land rover owners who have come to start their car mainly, turned the key and its rolled off down a hill - the earth braid has broken, and the handbrake cable is all that is left for an engine earth!

They dnt like 600 amps through them

 

[gavuk]

I've used this for years no problems yet .....not on my 20 year old golf at least surge protector

 

[busastars]

I go one of those surge protectors (different make) but the only welding I do is on the bike, still got CDi and powervalve electronics.

 

[chris y]

I know of land rover owners who have come to start their car mainly, turned the key and its rolled off down a hill - the earth braid has broken, and the handbrake cable is all that is left for an engine earth!

Surely not the handbrake cable, which has nothing to do with the engine at either end.
Im sure that what you say could easily happen to the accelerator or clutch cable on many cars though.

I have inadvertantly welded through a brake cable on a motorbike when I was young, the rear end was otherwise rubber mounted.
The cable was destroyed in a puff of smoke.

As for welding cars, I have worked on quite a few including 90s ones with plenty of electronics, I always disconnect the battery, make sure of a very good earth right beside the welding job and have had no problems.
That doesnt mean I think Im right, just stating my experience.

I did recently forget to disconnect the battery as it was flat, I stupidly thought I must have left it disconnected from the previous day.
It didnt cause any problems but I will always disconnect in future.

 

[pitmole]

The reason it can happen on a landrover is because they are all fitted with a transmission mounted handbrake on the rear propshaft output from the transfer case, unlike a normal car where, as you are correctly thinking, the handbrake operates on the rear wheels!

 

[boydy1989]

what pitmole said. the handbrake cable goes from the back of the 'box, which is about a foot away from the starter.

The other end goes to the seat box, about 2 feet away from the battery

 

[shenion]

The reason it can happen on a landrover is because they are all fitted with a transmission mounted handbrake on the rear propshaft output from the transfer case, unlike a normal car where, as you are correctly thinking, the handbrake operates on the rear wheels!

Still would be an issue if the cable was to the rear wheels.

The entire drive train is mounted on rubber mounts on most cars/trucks. Only ground is the braided straps. Would conduct down driveshaft, rear axle then cable.

Another possible ground is the speedo cable.

 

[Robotstar5]

Still would be an issue if the cable was to the rear wheels.

The entire drive train is mounted on rubber mounts on most cars/trucks. Only ground is the braided straps. Would conduct down driveshaft, rear axle then cable.

Another possible ground is the speedo cable.

Another one is the heater & choke cables on a Mini if the earth braid to the engine breaks

 

[chris y]

The reason it can happen on a landrover is because they are all fitted with a transmission mounted handbrake on the rear propshaft output from the transfer case, unlike a normal car where, as you are correctly thinking, the handbrake operates on the rear wheels!

Thanks for the education, I have learned something new (dont comment on stuff you dont know about)

 

[NTwoO]

Most of these examples involve a bearing or two. If your welding current goes through a bearing, that is the end of the bearing.