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Oxygen Sensors?

This is a discussion on Oxygen Sensors? within the Technical / Maintenance forums, part of the General Discussion category; A little background - My 98 silverado has 136k miles - I have very little, to no, top end - ...

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    Oxygen Sensors?


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    A little background - My 98 silverado has 136k miles - I have very little, to no, top end - I get, what I consider, poor gas mileage - in the 11 to 13 mpg highway. Changed the plugs and wires about 10k ago. No misses. No oil leaks. I love my truck but I have very little power. I am considering changing the front o2 sensors. I thought I read on this forum about disconnecting the o2 sensors and see if the truck runs the same. I have and it does. Any ideas on if I should proceed with the o2 sensor replacement or look elsewhere? I really appreciate your time.

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    Re: Oxygen Sensors?

    Change your fuel filter to. I don't know about your o2 sensor(s).

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    Re: Oxygen Sensors?

    Quote Originally Posted by mikec1974
    A little background - My 98 silverado has 136k miles - I have very little, to no, top end - I get, what I consider, poor gas mileage - in the 11 to 13 mpg highway. Changed the plugs and wires about 10k ago. No misses. No oil leaks. I love my truck but I have very little power. I am considering changing the front o2 sensors. I thought I read on this forum about disconnecting the o2 sensors and see if the truck runs the same. I have and it does. Any ideas on if I should proceed with the o2 sensor replacement or look elsewhere? I really appreciate your time.
    I would suggest changing all 4 O2 sensors. It may be overkill, but it doesn't sound like they have been replaced based on your post. As old gezzer mentioned, changing your fuel filter is a good idea as well. Are you registering any codes? Might want to check/clean your EGR valve...though typically there is a code thrown prior to that needing to be done.

    You might want to check the pre-/post-cat temps to see if your cat is functioning properly. If it is on the verge of going out, your pre-cat temps will be significantly higher than your post-cat temps. Reason I mentioned this is because you complain of top-end power, which is related to higher flow rates....
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    Re: Oxygen Sensors?

    IMHO.......Why change O2 sensors unless the computer throws a code?? Check your codes......IF not, why have a computer in there?? O2 sensors are expensive like $50 each.

    Aloha, Mark

    PS.........and IF you can SCAN IT........better yet.
    Last edited by ma96782; 10-02-2006 at 12:22 PM.
    '95 Silverado ECSB, K1500, Z71, 4x4, 5.7L, TBI, 4l60e 4 spd auto trans, 3.73, G80, LT245/75R16, alum 6 lug wheels, 6 leaf springs on each side, 14 bolt rear, disc/drum (Code JB6-7200 lb rated), 6600 GVWR (Code C5S), HD chassis (Code F44).........basically stock.

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    Re: Oxygen Sensors?

    O2 sensors have a life expectancy. Once they have exceeded that expectancy they may still function, but they begin to operate slower and erratically. You won't always get a code, but your mileage will suffer. Stick with GM sensors. The cheaper aftermarket ones tend to cause problems. Unfortuately, GM sensors are considerably higher priced. The one on my 95/5.7 was $90 at the dealer, but I haven't had a problem with it since it replaced a cheapo Bosch sensor.
    Last edited by lmadore; 10-03-2006 at 10:06 AM.

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    Re: Oxygen Sensors?

    I am having some of the same trouble out of my 96 Z-71 with a 5.7Ltr 350. In doing some research the common time to change your O2 sensors is every 25K or if you pull it out. Thta is what has been on several websites, but like it has been said, O2 sensors are about $40-$90 each and there are four of them. I have a code reader and there is only a code showing for one sensor, but the code does not really tell you which one. It was for the #1 Bank and the #2 sensor. Does anyone know which side the number one bank is on?

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    Re: Oxygen Sensors?

    Got this from a FORD forum.....should be same for all vehicles using OBD II codes (I could be wrong):

    The Federal Test Procedure Catalyst Efficiency Monitor is an on-board strategy designed to monitor and determine when a catalytic converter has deteriorated below the minimum level of effectiveness in its ability to control exhaust emissions. This monitor relies mainly on the front and rear Heated Oxygen Sensors (HO2S) to infer catalyst efficiency based upon oxygen storage capacity. The front and rear HO2S switches are counted under specified conditions for the purpose of calculating a rear-to-front HO2S switch ratio. After the switch ratio is calculated, it is compared against an emission threshold value. If the switch ratio is greater than the emission threshold, the catalyst has failed. The oxygen storage capacity of a high efficiency catalyst will have a low switch ratio and high HC efficiencies. As catalyst efficiency degrades, its ability to store oxygen declines and it will begin to have a higher switch ratio and low HC efficiencies. In general, as catalyst efficiency decreases, the switch ratio increases. Inputs from the ECT, IAT and TP sensors are required to enable the Federal Test Procedure Catalyst Efficiency Monitor.

    1. In the Federal Test Procedure Catalyst Efficiency Monitor test, only switches during steady state cruise conditions of a drive cycle are counted. Switches at idle or other drive modes are not counted. The counting of front and rear HO2S switches continues until a drive cycle is completed. At that time, the ratio of total rear switches to total front HO2S switches is calculated. If the switch ratio is greater than the emission threshold, the catalyst has failed and a Diagnostic Trouble Code (DTC) is stored.

    The DTC associated with this test is DTC P0420.

    DTC P1408 is similar to P0401 but performed during KOER Self-Test conditions.

    2. The MIL is activated after a fault is detected for up to six consecutive drive cycles.
    AND...
    The HO2S/O2S Monitor is an on-board strategy designed to monitor the HO2S/O2S sensors for a malfunction or deterioration which can affect emissions. The fuel control or upstream HO2S/O2S is checked for proper output voltage and response rate (the time it takes to switch from lean to rich and vice versa). Except on Aspire, the HO2S heater circuit is monitored by detecting proper voltage change as the heater is turned on and off. Downstream HO2S used for Catalyst Monitor are also monitored for proper output voltage. The illustration below shows that input is required from the ECT, IAT, MAF, MC-VAF for 2.5L Probe, and CKP sensors to activate the HO2S/02S Monitor. The Fuel System Monitor and Misfire Detection Monitor must also have completed successfully before the HO2S/O2S Monitor is enabled. Except on Aspire, some of the HO2S Monitor checks are also performed during on demand self-test.

    1. The HO2S/O2S sensor senses the oxygen content in the exhaust flow and outputs a voltage between zero and 1.0 volt. Lean of stoichiometric (air/fuel ratio of approximately 14.7:1), the HO2S/O2S will generate a voltage between zero and 0.4 volt. Rich of stoichiometric, the HO2S/O2S will generate a voltage between 0.5 and 1.0 volt. The HO2S/O2S Monitor evaluates both the upstream (fuel control) and downstream (Catalyst Monitor) HO2S for proper function.

    2. Once the HO2S/O2S Monitor is enabled, the upstream HO2S/O2S signal voltage amplitude and response frequency are checked. Excessive voltage is determined by comparing the HO2S/O2S signal voltage to a maximum calibratable threshold voltage. A fixed frequency closed loop fuel control routine is executed and the upstream HO2S/O2S voltage amplitude and output response frequency are observed. A sample of the upstream HO2S/O2S signal is evaluated to determine if the sensor is capable of switching or has a slow response rate. Except on Aspire, a HO2S heater circuit fault is determined by turning the heater on and off and looking for a corresponding change in the Output State Monitor (OSM) and by measuring the current going through the heater circuit. The HO2S/O2S Monitor DTCs can be categorized as follows:

    The DTCs associated with HO2S/O2S lack of switching are DTCs P1130, P1131, P1132, P1150, P1151 and P1152. For the 1.3L Aspire and 2.5L Probe the DTCs are P0134, P0140, P0154, P0160, P1170, and P1173.

    The DTCs associated with HO2S/O2S slow response rate are DTCs P0133 and P0153.

    The DTCs associated with HO2S/O2S signal circuit malfunction are DTCs P0131, P0136, P0151 and P0156. The DTCs for the 1.3L Aspire and 2.5L Probe are P0130 and P0150.

    The DTCs associated with a HO2S heater circuit malfunction are DTCs P0135, P0141, P0155 and P0161.

    The DTC associated with the downstream HO2S not running in on-demand is DTC P1127 (Except 1.3L Aspire and 2.5L Probe).

    The DTCs associated with swapped HO2S connectors are DTCs P1128 and P1129 (Except 1.3L Aspire and 2.5L Probe).

    3. The MIL is activated after a fault is detected on two consecutive drive cycles.
    Now, back to the question which side is it? I don't know.....but,in a FORD:

    Bank 2 is the driver side.
    Sensor 1 is a forward sensor (in the exh manifold or y-pipe upstream of all the cats.
    And here is another guy, he switched sensors left to right (experiment):

    Since I followed some advice on this forum, I thought I'd share my experience for future readers.

    I too had a P0430 code on my 98 5.0L V8 Ford Explorer, and an occasional exhaust smell in the truck when stopped at a light. Summary of advice I've seen on forums regarding this code:

    1) Ford indicated a bad O2 sensor will not cause this code, only a poorly functioning cat.
    2) While they cat is bad, you need to find out the upstream cause of the failed cat, or you'll just fail another one.
    3) Neglecting 1) above (not everyone agrees it can only be the cat), switch the rear O2 sensors between bank 1 and bank 2. If it really is the cat, should still get a P0430, if its the O2 sensor, the code would switch to the other bank (P0420).

    I decided to try 3) (shouldn't hurt, although some on the forums say a bad cat will damage an O2, so I may have to replace another O2 as well)

    I also decided to replace my spark plug wires and plugs as a potential "upstream" cause. I'm a "go to the doctor only when I'm sick" type, and apply the same philosophy to my cars (and only when their real sick) so it should come to no surprise that the original 1998 wires were still on the car after 160,000 miles. (and the wires seemed like they were in extraordinarily good shape for an 8-year old, neglected car). Any rate, new Bosch wires, new Bosch Platinum+4 plugs (decided to splurge).

    End result? After reacting to a new code of P0106/noisy acceleration due to knocking off a small hose when replacing the wires (another fix I found on the forums, thank you!), Check Engine light is out, and no new codes for 600 miles! (note the problem didn't switch banks, it disappeared. Dirty sensor?, bad connection? Who knows). Occasionally still notice a slight exhaust smell, but can't tell if its my car, or being pulled up too close to the cars exhaust pipe in front of me.

    Car also seems to have much better power due to the new wires (and perhaps more expensive plugs).

    Hope this helps someone in the future. I learned a lot, and potentially saved some bucks.
    Anyway.....good luck.

    Aloha, Mark
    Last edited by ma96782; 10-04-2006 at 03:42 PM.
    '95 Silverado ECSB, K1500, Z71, 4x4, 5.7L, TBI, 4l60e 4 spd auto trans, 3.73, G80, LT245/75R16, alum 6 lug wheels, 6 leaf springs on each side, 14 bolt rear, disc/drum (Code JB6-7200 lb rated), 6600 GVWR (Code C5S), HD chassis (Code F44).........basically stock.

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    Re: Oxygen Sensors?

    BTW.....what was the code number?

    P0171, P0174???

    Aloha, Mark

    Hope you're not using one of those oil on the air filters, before the MAF?

    PS......http://www.explorerforum.com/forums/...d.php?t=149646
    Last edited by ma96782; 10-04-2006 at 03:44 PM.
    '95 Silverado ECSB, K1500, Z71, 4x4, 5.7L, TBI, 4l60e 4 spd auto trans, 3.73, G80, LT245/75R16, alum 6 lug wheels, 6 leaf springs on each side, 14 bolt rear, disc/drum (Code JB6-7200 lb rated), 6600 GVWR (Code C5S), HD chassis (Code F44).........basically stock.

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    Re: Oxygen Sensors?

    First I would take those cats off. And second, well actually that was it just take the cats off.
    2004 Escalade, bone stock

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    Re: Oxygen Sensors?

    on this issue, i see mentioned there are 4 O2 sensors. would ya'll enlighten me as to the 4, being on the i am unaware of 3 of them?

    thanks
    93/94 Z71 4x4 ExtCab Shtbed Bone Stock

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    Re: Oxygen Sensors?

    I don't know about on a 98 model but on my 2000 there are two cats before the pipes go to one....and there is an O2 sensor before each cat and after each cat. The one's before are responsible for making adjustments to the fuel ratio whereas the ones after do nothing but monitor the effectiveness of the cats. I would just replace the pre-cat ones and only replace the post-cat ones if they are throwing a code and you want the "service engine soon" light to go away.

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    Re: Oxygen Sensors?

    Man, this forum rocks!
    I've been a little busy so this is the first time I've been able to check back on my post. I really appreciate everyone taking the time to read and/or reply to my post.
    So, a little update: I hooked the O2's back up and replaced the fuel filter, PCV valve, rotor cap & button. Truck does seem to run better with better acceleration but still not where it should be. I guess my next steps are:
    1)Clear the codes and run the truck for while. Check for any codes.
    2)Replace the front O2's and see what happens.

    Like I said before, I originally disconnected them and found no difference in the performance of the truck. Just an observation.

    I will continue to check on this posts updateds. I will also post back with the 02 replacement status.
    Thank you once again guys!

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    Re: Oxygen Sensors?

    I was greasing my truck today and noticed the cat was hot enough to fry an egg on, but the crossover pipe and muffler were both cool enough to put my hand on. Am I due for a cat? I know for sure I am due for an 02 sensor, it looks like the original (so is the cat).

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    Re: Oxygen Sensors?

    so are the cats supposed to be cold to the touch? Cuz mine are boiling water on contact.
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    Re: Oxygen Sensors?

    No, not cold. The heat is what makes them work. But too much heat and a rich condition will cause them to go bad, melt and break apart or clog up causing the truck not to run very good.

 

 

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