Hey all,
my 98 150 has 4 o2 sensors, are they all the same? Any advice, wisdom, dos or don’ts for sourcing and replacing them?
heath

 

Not sure but you can go to Rock Auto's site, look up your parts and see if the O2 part numbers are the same. They last a long time in a PROPERLY running engine. A code for an O2 sensor most of the time is representing a symptom of another problem and the sensor is just doing its job.. Unless you prove one faulty, I would leave them alone. I have two 87's and they still have their original O2 sensors.

 

well the the check engine light came on and it started running really rich so I scanned and all 4 sensors are bad apparently. I’ve attached the scan. there isn't any other fault codes that would suggest some other failure at this point. it's always run very well, so i can't imagine what would cause all 4 to fail at once.

 

The descriptions for the codes do not justify replacing all the O2 sensors.
There appears to be a failure of required power to the sensors and that last code is where I would start looking because that problem can affect all the O2 sensors which very well could have nothing wrong with them.
ALWAYS ,,,simple thing check for any blown fuses first.

 

I've checked all the fuses and no problem there. but i noticed that when i cleared the codes the mil goes off and it seems to run quite well, for a while. after about ten minutes the mil is on again and it's running rich. i also noticed that it runs relatively well when cold and gets worse as it warms up.
i also get readings from each sensor while it's running so they seem to be doing their job, which makes it sound like there's something wrong with the ecu, god forbid.

 

Always questions.
Did anyone do any kind of work in the engine compartment?
If so , what kind?

The reason I ask is there is a good possibility someone left off a ground wire someplace that involves the ECM.
The oxygen heaters are not getting power to function correctly and the codes are telling us that, plus the code involving power to certain parts needs to be checked out. There is a power supply relay in the ECM that supplies power to certain areas. If that relay is not functioning for whatever reason a lot of things can't work
We always rule out all other possibilities before replacing an ECM. The good part is programming the ECM on this vehicle is not necessary, but it is no fun after you replace the ECM and still have the same problem.

 

There has been no work done at all. I was driving one day and it just happened. Before then, there were a couple of occasions when it didn’t star right away as usual and seemed to be flooded, but cleared up after a few seconds.
is th relay in the ecm?
i’ll have to track down the grounds and check them.

 

Ok, I went through the wiring diagram and checked all the grounds and they are all good. The pcm relay is working because it also controls power to the fuel pump and it’s working properly. I do have heater power at the o2 sensor connectors but I haven’t verified that the ecm and the rest of the circuit is working. That’s the next step. But I was checking the scanner and all 4 sensors are reading well when it’s hot, fluctuating around 600-800mv but it shows 0.0% trim on both banks in short and long term. I don’t like the thought of that. Any wisdom about the trim? Also, as I mentioned before, it actually runs ok when it’s cold.

 

If you disconnected the battery, it will take a while for long term trim information to be reliably displayed. Short term should be present and constantly changing according to engine speed and conditions but it may take some start/stop cycles if you disconnected the battery.I am glad you didn't replace the O2 sensors because I think they are working and doing their job.
You stated you checked the grounds, hopefully you removed each one and cleaned them. Visual means nothing. The ground(s) for the computer usually are located behind the lower kick panels. Hopefully you checked them too.

 

I had to drive it yesterday, put about 100km on it, start and stop, so I’ll check the trim again and see if the computer has woken up. I did remove and clean each ground before reassembling them including the two in the left kick and the one behind the right kick.