I have a 3" long hairline crack in the exhaust pipe less then an inch from the oxygen sensor. Can this cause the misfire and stall symptoms that I am experiencing? If I weld the crack without removing the sensor could the heat damage it.
I doubt it's the cause of your miss & stalling, but once welded up you'll be able to tell.
Arc weld or torch weld?
O2s can take a lot of heat... the arc weld I'm not too sure about because of how close it is, but should be OK provided the ground clamp is placed close to the weld.
Monitor the O2 signal with a volt meter before you fix it and after... keep track of how long it stays lean, how long it stays rich and how many times it switches from lean to rich in a given time. The better your multimeter is the more accurate your test results... cheap meters will not be able to capture quick voltage switches accurately.
The Fluke 88 line is a great Multimeter that has a bar graph under the digits for monitoring O2 voltage changes.
I had a similar problem, although I had more than a hairline crack. (There was a break in the exhaust pipe where it bolts to the pipe closest to the engine). The result of this was a severe loss of power, to the point where the van would barely move, and it was blowing blackish exhaust. I presume these symptoms were due to an excessively rich mixture. Once I head the pipe welded, these symptoms went away.
I agree, get it welded, even if it doesn't solve your immediate problem it is sure to become a bigger problem in the future. Alternatively, you can get a new pipe for about $100 CDN from California Imports.
I replaced the pipe that was cracked ($50.00 + shipping from EVWPARTS.COM) and also needed to replace one of the manifold gaskets where it bolts to the head. The gasket failed and was letting exhaust blow by. The system is now closed and the surging I was experiencing has gone away. I did not need to replace the 02 sensor.
Hey, I was wondering along this lines...I have recently purchased my first Vanagon (2 1985's:I have actually one for parts too that has sat for a couple of years) and was told from a local shop that I didn't need the O2 sensor (They plugged it with a spark plug) Is this true? The reason why I am asking is that the van Idles great (Of course I gave it a tune up with the correct Bosch wires and Plugs, air filter, fuel filter, rotor and Dist Cap), but when I shift gears or try to get some real acceleration just after started, it won't want to give me the proper acceleration (kind of like maybe there's something stuck) I have been looking into to vacuum leaks, and it's plausible that the Injectors need replaced...maybe the tranny's shot? Any suggestions of where to start first...
The engine will run better with the O2 connected... provided the O2 is in good working order. It will run perfectly fine with the O2 disconnected, but fuel economy will decrease... not sure how much as I have never kept track with my own car (similar fuel injection system).