Emission Blues
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New User
Joined: Jan 2004
Posts: 20
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From: Lake Tahoe (prior 13yrs)
Emission Blues
I gang.....I have a 88 BII 2.9 auto/4x4 f.I......passed CA pre-test smog with flying colors. then smog machine died....12 miles later, went to another smog shop....failed/gross polluter at an idle. HC max=120 mine=367........Co max=1.0 mine=1.53......anyway, I was testing O2 and it was 400-500mv the 3min-7min.....at 7min it began to show 800mv sometimes. Then at 10 minutes of engine idling it shot up beyond 1.8mv. So what did el Cheapo do? I put in a used O2. Sure sounds better. Before I go to smog re-test, i tested O2 signal........it stays at about 925-935mv. My question is.....isnt' it supposed to fluctuate from low numbers to this number? Or is this a sign my El Cheapo Used part is bad? My fuel pressure is 40 key on, then drops to 33 psi engine on. All my spark plugs (new and gapped 42) showed signs of some black. ( I was looking for a possible one cylinder weak spark/combustion). All spark plugs look the same. Thanks gang and I expect a beating for using used parts.
Post Fiend
Joined: Dec 2001
Posts: 10,562
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From: South Jersey
Welcome to FTE!!!
It should fluctuate around 0.5V (0.2-0.8). I would suspect a bad senser or a leaking fuel pressure regulator causing a rich condition. High numbers are rich, low are lean. Have you pulled the codes?
It should fluctuate around 0.5V (0.2-0.8). I would suspect a bad senser or a leaking fuel pressure regulator causing a rich condition. High numbers are rich, low are lean. Have you pulled the codes?
Thread Starter
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New User
Joined: Jan 2004
Posts: 20
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From: Lake Tahoe (prior 13yrs)
Thanks for the welcome and the response Ken00............................Here's today's news. Because I had the stuck O2 sensor reading of 900-925mv, I was about ready to go buy another O2. As I was taking readings again, the O2 seemed to jump into action by giving me readings between 150mv-800mv (fluctuating). I decided to drive to smog shop. The truck sure seemed peppy! Just before getting a smog reading, I checked O2 signal again. It was good, still fluctuating. Guess what? My smog reading were back to normal. HC=120 and dropping (smog guy said s. plugs will continue to clean up.......CO=.05......Here's my last question.......Is it possible......that when installing a replacement O2, that the computer has to go thru an adjustment cycle? I mean, an adjusting time frame? for the replacement sensor? It probably took a total time of 25 minutes for the new readings/computer adjustments(?) to take place.
Post Fiend
Joined: Dec 2001
Posts: 10,562
Likes: 4
From: South Jersey
The O2 sensor is only used in closed loop, which is when the engine is warmed up so its possible you were taking reading while still in closed loop. Open loop would have a rich condition just like having the choke on. Also the computer will go into failure mode when it detects a defective sensor but I believe it will discontinue this mode when a "normal" reading is obtained from the senser.
