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Strange - oxy sensor maybe?
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belliott
Novice
Sep 22, 2006, 8:25 AM
Post #1 of 11
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Strange - oxy sensor maybe?
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Just finished a complete exhaust job on my 1993 GMC 3500 with a 350 and AT. Replaced everything from the manifold back including the oxygen sensor before the cat. covt. Now she won't start and is choking black smoke while trying to start! This was only a exhaust job and she ran fine before -- any ideas-- has the new oxy sensor fried my computer??
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Sep 22, 2006, 9:36 AM
Post #2 of 11
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Re: Strange - oxy sensor maybe?
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That is strange!!
Why did you replace the o2 sensor?
Any chance if you used torches that some wiring got messed up?
Just a thought. Anybody else have ideas here?  T
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belliott
Novice
Sep 22, 2006, 9:40 AM
Post #3 of 11
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Re: Strange - oxy sensor maybe?
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no flames - just unbolted and dropped the old. Old sensor had welded itself with rust to old pipe so a new one was only $18.
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steve01832
Veteran
Sep 22, 2006, 11:06 AM
Post #4 of 11
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Re: Strange - oxy sensor maybe?
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Unplug the O2 sensor. With a digital multimeter, set volt scale to 12vdc. Turn key on engine off and test O2 sensor plug on vehicle side. If you have approx. 1/2v the computer is fine. I'm assuming this is a single wire O2 sensor. Computers look only at the O2 sensor voltage after the engine is at operating temp. It shouldn't affect a cold start. My question is "Did you use a welder when you did the exhaust or was it slip on with clamp)? A mig welder can send high voltage back on the vehicle frame and can spike a computer if you leave the battery connected! OOPS
(This post was edited by steve01832 on Sep 22, 2006, 11:13 AM)
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belliott
Novice
Sep 22, 2006, 11:10 AM
Post #5 of 11
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Re: Strange - oxy sensor maybe?
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no it was a slip on with clamps. no electrical charge at all because the battery had been disconnected before I worked on it
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steve01832
Veteran
Sep 22, 2006, 11:15 AM
Post #6 of 11
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Re: Strange - oxy sensor maybe?
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Can you hear the fuel pump run when you turn the key on? Is it possible the harness got yanked by a pipe or muffler during tear out?
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belliott
Novice
Sep 22, 2006, 11:21 AM
Post #7 of 11
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Re: Strange - oxy sensor maybe?
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Yes that why this is so puzzling - I took the exhaust off and disconnected the o2 sensor and she still won't start and is choking on black smoke like incomplete burning of fuel.
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steve01832
Veteran
Sep 22, 2006, 11:27 AM
Post #8 of 11
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Re: Strange - oxy sensor maybe?
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Can you smell fuel if you crank the engine for about 20 seconds? If you can, let's check for spark at a plug wire.
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belliott
Novice
Sep 22, 2006, 11:34 AM
Post #9 of 11
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Re: Strange - oxy sensor maybe?
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Yes, she's trying to start but she can't catch her breath! It's a throttle body injection and the only thing I can think of is the timing is out of sync or the computer is behind or ahead in it firing order???
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steve01832
Veteran
Sep 22, 2006, 11:36 AM
Post #10 of 11
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Re: Strange - oxy sensor maybe?
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Did you confirm spark?
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belliott
Novice
Sep 22, 2006, 11:38 AM
Post #11 of 11
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Re: Strange - oxy sensor maybe?
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Not yet - I'll have to get back to you because I'm away for the truck right now -- I will check the dist cap also maybe it's cracked-- thanks for your time
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