So I was driving through some big puddles and my exhaust ripped apart at a rusty junction. It drove perfectly back home. I cut off the bad section and MIG welded it back together. Went for a shakedown and after a minute it wouldnt accelerate. On the slightest up hill grade it almost stopped moving all together and couldnt build up enough momentum to get out of first gear. Back in my driveway in park, the engine fumbles when i give it gas, although it idles well. If I keep on the gas it will stall eventually. My fear is that my mig fried something. Or is it just coincidental? I unclipped what im pretty sure is the O2 sensor from the exhaust manifold down pipe and it runs exactly the same(?), problem still there. If I did fry something, this seemed logical due to its proximity to the weld site. I have yet to check the plugs, distr., fuel, etc.. Has anyone ever experienced these symptoms? Has anyone fried electronics with a mig welder? I have welded on vehicles before and never had a problem. Thanks for any help, I need it! Also, Im not sure if this helps but its a '90 with a renix 4.0 and 220k miles on the clock.

 

sounds to me like you messed something up with the o2 sensor. if it becomes faulty it will begin to dump fuel and cause it to run like crap

 

Sounds like a partially plugged exhaust.

 

I would say its the O2 sensor. I have never personally fried any electronics with a MIG welder but i have seen someone els do it so it wouldnt surprise if the sensor is fried. Where did you place your ground?

 

I put the ground on the exhaust right next to where i was welding. Between the cat and the exhaust manifold down pipe. I also did not uplug the negative battery terminal which in after thought, would have been smart.

 

unplug the cable and touch the other terminal to reset the memory and see if that works.

 

Reset the memory and problem is still there. So, I sprayed the 02 sensor w/ PB blaster in preparation for its removal. Hopefullu it comes out easily, and a replacement will fix all.

 

Did you unhook your battery when you were welding?Sorry read right over that part

 

yea.

 

sounds like you welded before disconnecting the battery and now your ecm is toast

 

Hopefully the O2 sensor is your problem. I learned the hard way to always remove the negative cable when welding on a vehicle. Had to pay out of my pocket when I fried the pcm in a truck I had worked on.

 

So here is an update on my situation. I bought a junkyard ecm and installed it. Fired up the jeep and problem still there. New 02 sensor and problem still there. I dont think it is a clogged cat because it is a high flow cat converter that is a little less than a year old and I feel plenty of gas exiting the pipe at idle. I think I might have to check all the sensors one by one which would be a real PITA! Do my symptoms sound like any of the sensors that I havent replaced?? Also, i noticed that the exhaust smells stronger (not unburned gasoline smell though) than before (I think, or maybe Im crazy). This is starting to dive me nuts.

 

I would check the fuel pressure & flow......
Good luck!

 

Any chance the O2 sensor was bad out of the box? How about burned wires from welding? I read a lot about a bad O2 sensor making it run too rich.

FWIW I did some exhaust welding recently. At the time I didn't think (know) about dropping the negative terminal. I lucked out and nothing happened.

 

somethings fried, ECM, O2 sensor etc. check ebay for ECMs, I got one for a buck plus shipping.

Sorry, missed that post. Have you checked your fuel pressure? Its also possible an injector was fried?? Also always disconect Neg terminal when doing any unplugging or plugging in of electronics. Good luck.