I have many car manuals, such as Haynes and Chiltons, Alldata. The scheduled minor and major tuneups, (3k, to 30k miles) and beyond, never call for a routine check or replacement of the Oxygen sensor. Those books say to replace it, if it is bad, but not a routine maintainence item.

I have heard one person tell me that his manual does call for a replacement, but he did not say what manual, nor did he offer to say at what mileage, nor what type shop he works at.

I am wondering if that is just the opinion of non-Ford shops. I would like to hear from someone who can identify alleged source for replacing the sensor, if it exist.

 

I would have to say that you could probably pull it out @ around 60,000 which is when most emisions maintaince is suppose to be done and take a look at it. If it looks dirty, black or coroded then indeed it would probably be a good time to replace it.

[center]

[font color="blue"]
Mudslinger_82 aka Mike G

[/font]

http://farmall_h.tripod.com/tractors_files/Animated/257.gif
[font color="red"]
[marquee]Ford Power All The Way, If it ain't broke don't fix it.[/marquee][/font]

 

[font size="1" color="#FF0000"]LAST EDITED ON 31-Jan-01 AT 00:16 AM (EST)[/font][p][font size="1" color="#FF0000"]LAST EDITED ON 31-Jan-01 AT 00:11 AM (EST)[/font]

[font size="1" color="#FF0000"]LAST EDITED ON 31-Jan-01 AT 00:05 AM (EST)[/font]

[font size="1" color="#FF0000"]LAST EDITED ON 31-Jan-01 AT 00:00 AM (EST)[/font]

[font size="1" color="#FF0000"]LAST EDITED ON 30-Jan-01 AT 11:59 PM (EST)[/font]

Thanks for the reply. I do hope to peak inquirying thoughts on this topic. Your reponse, however, reflects the general opinion that many share, and that I seek to substantiate in the form of car manufacturer documentation. I have never seen, in any official manufacturer document, i.e. Ford service manuals, that the O2 sensor should be replaced. I see many case's where the problem description includes a history of replacing the O2 sensor, "..but it did not fix the problem..".

So, I merely seek the answer to the question; What book, or service manual, recommends changing the O2 sensor based on mileage alone. I have never seen any such thing in print. If you work at Firestone or Goodyear or Ford or any car repair shop, I would like to hear from you. There are many consumable components, such as hoses, belts, filters, but nowhere do I see that sensors be routinely replaced. In fact, there is much documentation from every repair source, that explains the role of the sensor in alerting the car owner to emissions problems. As they say, don't kill the messenger, just for giving you the message. My point is that the O2 sensor is the messenger, not the cause, in the majority of cases.

It is even documented that most contaminants, i.e. carbon and coolent, will burn off the sensor tip after an hour of driving on the freeway.

I respectfully reiterate; What document states that a O2 sensor should be replaced as part of a minor or major scheduled tune-up? I would like to point out that Ford is precise and explicit when it comes to the check list of tune up items for the recommended schedule of maintainence. This "scheduled" maintence list is no secret. It is available to anyone who wants to see it. Perhaps the average home mechanic has always glossed over this chapter in the Haynes and Chilton manual, in search of their immediate car problem topic, but that information has always been published. And it is based on the published manufacturers recommended maintainence.

Are we to believe that a new O2 sensor is as worthwhile as new plug wires? Plug wire replacement, although expensive, and not always needed, are a part of routine documented replacement for some cars. But I do not see the O2 sensor listed on the check list. Does anyone?

I have tested O2 sensors that car owner have wanted to replace; in fact, they have already bought new one's at the price of $120 for 2. I have never found a defective O2 sensor. The test is as quick and easy as any voltage test I have perfomed.

It truely seems to me that replacing these sensors is convienent and profitable for shops for several reasons, including the remote possibility that it may be faulty. I understand that form of economics. But, I seek to learn the true economics of replacing $120 worth of sensors when it has never been promoted by the manufacturers.

Sorry to be long winded. Can you feel my frustration?

 

If you have axcess to a lab scope you can watch the activity response of the sensor under a varitity of conditions. There are classes that teach how to interpret what you see. O2 sensors will get "lazy" sometimes and not really cause any noticable problems other than a loss of fuel mileage. It can take some time to hook up and watch but you can see a lazy O2 pattern If you can afford to spend the time. When O2 sensors first came out your owners manual would tell you that when the emissions light came on at 60k, 90k, whatever, you were to have the sensor replaced, EGR checked and light reset. When check engine lights came into play I no longer remember seeing any replacement intervals.













2000 XLT Flare Supercab Sport 5.4-Auto-355LS-Tow pkg-Bedrug-Xtang Tonneau

 

Thanks for that very informative reply.

Now that you mention it, I would love to have a lab scope but I don't think they make any for under $500 do they? You have touched on a interesting point about lazy injectors. My DMM tester will show activity and voltage levels, min, max, average, but I have not taken a class in O2 testing, so I can't be sure they are 100% operation. For example, would you know if a min and max voltage reading of 250mv / 950mv is normal at idle. It seems a bit of a wide swing to me, but 100mv to 900mv is within the correct operating range, or close to it.

I do seem to recall the early model 'emissions light' which has now been replaced with the 'check engine' light.

Thank you.

 

O2 sensor range is 0 to 1 volt. In reality they will range from a low of .2 to 1.3 volts. It should crossover several times a second. Called O2 crosscounts on a scan tool. Refers to the number of times the reading switches from rich to lean and crosses the 450 mv center line. As for a lazy O2, you will need a lab scope to see the slow responce time. DVOM's just are not fast enough.



2000 XLT Flare Supercab Sport 5.4-Auto-355LS-Tow pkg-Bedrug-Xtang Tonneau

 

Sooooo Do we replace the old O2 sensors or not? I am totally confused but your conversatation... I was always under the impression that the O2 sensors should be replaced at the 60k milage mark! PLEASE clear up my confusion if you can....

Mike

 

Personaly I don't like to change anything until I can prove why. Just for my own info. and because I wanted to see if I might have found a reason for another problem I've had I did a lab scope test on my own 02 sensor. Scope says its working great. 115,000 miles on it. Its an 89 and then I've changed out lazy 02's on 97's so go figure.


2000 XLT Flare Supercab Sport 5.4-Auto-355LS-Tow pkg-Bedrug-Xtang Tonneau

 

Hi Nitro,

You da man! Glad to hear from you. I have read that 8 crossings per 10 seconds is the rule. But unfortunately, WHAT rule are they talking about? I am unsure which of the two it is:

1. 8 per 10 sec is the MINIMUM crossings. 7 or less or not good.

2. 8 per 10 sec is the AVERAGE crossings. 6 or 7 is acceptable.

Could you clear up which of the above is the 'rule'?

Also, if a DMM function for Average millivolts, reads 650 instead of 450, yet has 10 crosscounts per 10 sec, it that considered acceptable for the sensor?

 

450 mv is the centerline. Above is rich, below is lean. First the sensor has to be hot (600°) and computer in closed loop before any 02 reading can be evaluated. 8 crosscounts is a reasonable rule of thumb or average but only a part of the picture and not a condemning factor by its self. On a snap throttle you need to see volts spike to at least .9mv and dowm to .2mv and on steady fast idle say 1500 rpm you should see a even pattern that resembles a sine wave pattern crossing above and below the centerline. So in my opinion I don't condemn one just because it doesn't cross but 4 or 5 times. I want to see it hit high and low and not have a lazy pattern. I'm not an expert at lab scope patterns so I remain open to new and better informaton. Hope this makes sense.



2000 XLT Flare Supercab Sport 5.4-Auto-355LS-Tow pkg-Bedrug-Xtang Tonneau

 

Thanks again Nitro.

You have cleared up quite a bit for me. However, I still confuse the readings for a 'good 02 sensor' with the performance of the car. For example:

1. I believe this 02 sensor is sound and good, but that doesn't mean the engine is running avg on fuel consumption.

2. Thus the 650mv Average reading, indicates an engine that is running rich, is that right? ? ?

Sometimes I simply get confused between a 'good' sensor, and a 'good' running engine. In this case, I think I have good sensor but rich engine.

The owner says he gets poor gas mileage, but I can't pull codes with a scanner for the 96 Ford OBDII. But the check engine light is always on and the truck runs fine.

 

Yes, if the reading is staying at 650mv most of the time I would agree that the engine is running rich and the sensor is just doing its job. This is where scan tool and lab scope info. would keep the guess work down. Scan PIDs can reveal a lot of info but you must remember that it is only a snap shot of real time so you miss a lot of action that lab scopes don't.


2000 XLT Flare Supercab Sport 5.4-Auto-355LS-Tow pkg-Bedrug-Xtang Tonneau

 

A local mechanic where my dad takes his truck says the 02 sensor should be replaced every 50,000 miles. My dads truck 92 chevy didn't pass emmisions until we replaced the sensor at 119,000 miles the only time it was replaced the check engine light was not on. My mom has a 96 hyundai which had like 56,000 miles when the check engine light came on it needed the sensors. I guess it depends on the vehicle when it needs changed. With the OBDII the computer needs to be reset after they are changed.