Time for a new oxygen sensor?
Lead Driver
Joined: Nov 2002
Posts: 9,556
Likes: 43
From: Concord, NC
An O2 sensor is not like the other sensors on the vehicle. Most other sensors just change resistance and don't wear per se, but the O2 sensor generates a voltage output depending on the amount of oxygen present in the exhaust. I don't know specifically how it creates this voltage though. I've never gotten an O2 sensor code other than when it has been unplugged. I just replaced my O2 sensor a couple weeks ago, and it made the truck run much better. No code, but it had been 50-60000 miles since last replaced, and the truck was getting worse gas mileage than it had a while back. The readings the computer gets from the O2 sensor during closed loop fuel control can have some bearing on open loop fuel trims too. I don't think it is enough to cause the black smoke and stumbling at startup, but the computer adapts (at least to some extent) to what it sees from all the sensors.
Senior User
Joined: Jan 2005
Posts: 131
Likes: 0
From: salem now then boxford
guess i can't say *******...oops...****...
hahahaha
anyway, my car kinda matches what your truck is doing...so the oxygen sensor is definitly an option worth checking out.
as for me i think i blew another sensor in my car...time to ge the 1977 F-250 on the road
hahahaha
anyway, my car kinda matches what your truck is doing...so the oxygen sensor is definitly an option worth checking out.
as for me i think i blew another sensor in my car...time to ge the 1977 F-250 on the road
Last edited by SasquatchF-250; Apr 20, 2005 at 12:06 AM.
Posting Guru
Joined: Jun 2004
Posts: 1,781
Likes: 1
From: Central NY
The o2 sensor doesn't come into play at startup. It will have an effect when the computer take control of running the engine.
Black smoke at startup is typically an over rich condition; possibly overpressurize fuel or leaking injector.
As FEFARMS suggested already, you need to check both the running pressure and the leakdown/bleedoff rate when you shut the engine off. The v8's have about 39psi running at idle and should hold withing 5psi when shutoff for 30 seconds.
Cheers,
Popa Tim
Black smoke at startup is typically an over rich condition; possibly overpressurize fuel or leaking injector.
As FEFARMS suggested already, you need to check both the running pressure and the leakdown/bleedoff rate when you shut the engine off. The v8's have about 39psi running at idle and should hold withing 5psi when shutoff for 30 seconds.
Cheers,
Popa Tim
Lead Driver
Joined: Nov 2002
Posts: 9,556
Likes: 43
From: Concord, NC
The O2 sensor isn't actively used at startup, no, but the computer does trim the fuel map in closed loop, which carries over to open loop. However, it's likely not going to trim the fuel map enough to let out a puff of black smoke.
Junior User
Joined: Feb 2005
Posts: 50
Likes: 0
From: Dallas, TX
Re: Need Oxygen Sensor ...
Gentlemen,
Iv'e got a '91 F150 Lariet, 300 I6 w/E40D & 80,000 miles ... Runs good. Been reading this thread. Question(s) ...
1. How many Oxy sensors does this beast have? ... I can see one in the Cat going to the muffler.
2. Do I have another Cat upstream?
Thanks, Clueless in Dallas
Iv'e got a '91 F150 Lariet, 300 I6 w/E40D & 80,000 miles ... Runs good. Been reading this thread. Question(s) ...
1. How many Oxy sensors does this beast have? ... I can see one in the Cat going to the muffler.
2. Do I have another Cat upstream?
Thanks, Clueless in Dallas
Elder User
Joined: Sep 2004
Posts: 941
Likes: 4
A 1991 I6 F150 has one oxygen sensor total. It should be in the exhaust system after the manifold but before the catalytic converter.
"After cat" oxygen sensors didn't come in until the advent of OBD-II and Federally mandated catalytic converter efficiency monitoring (1996 and later models).
"After cat" oxygen sensors didn't come in until the advent of OBD-II and Federally mandated catalytic converter efficiency monitoring (1996 and later models).
Junior User
Joined: Feb 2005
Posts: 50
Likes: 0
From: Dallas, TX
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Senior User
Joined: Dec 2004
Posts: 357
Likes: 0
From: Midwest Illinios
I had the same problem with the rough idle. My truck ran good but wouldnt idle for crap. After replacing the obvious plugs, wires, cap, rotor(which needed to be done anyway), it still idled horribly. I got a can of seafoam and ran through it and now she purrs like a kitten. This stuff definetly gets the thumbs up from me.
Senior User
Joined: Apr 2005
Posts: 109
Likes: 0
From: Canada
A LOT of peoplle don't realize that an O2 sensor is a "wear" item. But it is. Just like plugs, filters, etc. A lot of mechanics don't replace them either. They do age and wear out. They are the main source of info to your engine's computer.
I think an O2 is like a lot of people with imports etc don't realize a timing belt is normal to replace. They hear they have to replace it and go "Oh my God!" not realizing this is just a normal replacement item.
I think an O2 is like a lot of people with imports etc don't realize a timing belt is normal to replace. They hear they have to replace it and go "Oh my God!" not realizing this is just a normal replacement item.
Last edited by DenDanger; Apr 25, 2005 at 06:34 PM.
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