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Exhaust Leak - 02 sensor - related demons?
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Turbolou
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Joined: August 07, 2005
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PostPosted: Sun Mar 18, 2012 10:24 am    Post subject: Exhaust Leak - 02 sensor - related demons? Reply with quote

FINALLY got my 86 on the road, but I fear all may not be well with the world.

I think I've got it narrowed down, but with all the world-class minds on here, I wanted to check with you all. Stock 2.1L, top end rebuild. Here's what it does:

Starts and idles perfectly. When it gets warm, it chokes to death and stalls. It will fire right back up, but it won't idle for long before it just slowly dies.

I disconnected the Oxygen sensor, and it seems to run just fine, no more dying at idle. I drove it all over hell and back this weekend with no issues. I would, however, like to make it right because I know driving it with no oxygen sensor ain't right.

So I crawled around under there a little, and I noticed an exhaust leak at the collector before the bend that heads to the Oxygen Sensor and Catalytic Converter. It's not a HUGE leak, but it's definitely leaking there. My question is: Could that exhaust leak be causing the O2 sensor to give a faulty reading to the ECU, causing the engine to either over enrich or over lean the mixture, causing the engine to die? And, conversely, if I get a new pipe from the collector to the cat and reconnect the 02 sensor, it should work... in theory... correct?

One last little thing: I haven't been able to get the van completely up to temp to the point where the fan come on. I let it idle for what seemed like an eternity, but the gauge never got past halfway, and the fan never came on. I bled it with my libby bong, but I'm not completely convinced I did it correctly... ugh.

Bottom line: The damn thing is on the road, but I want it to be right!
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Currently:
1969 Beetle got it when I was 14, hoping to have it ready by the time I turned 16. Still in primer in my garage. I'm 38.
1986 Westy ("ALAN!")
2015 Golf Sportwagen ("Sabine")
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T3 Pilot
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Joined: January 10, 2011
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Location: Deep South of the Great White North
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PostPosted: Sun Mar 18, 2012 11:14 am    Post subject: Reply with quote

You are correct in presuming that a leak in the exhaust system upstream of the 02 sensor will give a false reading. That sensor is trying to measure the difference in O2 content between the exhaust gas and the outside air.

Repair the leak in the pipe or gasket, then dig into a copy of the digifant protraining manual and you can methodically troubleshoot your ignition system from the air filter to the tailpipe.

You sound like the type of owner that would enjoy going through the protraining manuals- there are 3 of them that I am aware of for your Van. Search and you will find, they are easily downloaded and should be kept in the van with your toolbox.

I was'nt really thinking about your cooling system, maybe someone else will chime in on that topic.
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The most important part in every vehicle is the nut behind the wheel......
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NorCalbuggy
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Joined: March 06, 2006
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Location: Tracy, California
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PostPosted: Sun Mar 18, 2012 11:21 am    Post subject: Reply with quote

You are probably on the right track with your exhaust leak theory.... a voltage reading from the O2 sensor before and after the pipe replacement would tell the tale
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1987 Westfalia Vanagon - "Clifford"
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NorCalbuggy
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PostPosted: Sun Mar 18, 2012 11:33 am    Post subject: Reply with quote

Chiming in on the cooling system - there is a lot of coolant, it'll take a while to build enough heat up (about 200 deg.) to trigger the fan operation
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1987 Westfalia Vanagon - "Clifford"
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