98 5.0, o2 questions

[white_shadow]

what is the rear o2 reading/measuring and telling the computer?

 

[thorney_5]

The rear o2 sensor essentially measures the efficiency of the catalytic converter. By comparing the output of the rear sensor to that of the front sensor, the computer is able to determine the catalyst's efficiency.

If the rear oxygen sensor goes out of a predetermined range, the computer will store either a catalyst efficiency trouble code, or one related to the circuit/shorts.

Here is a great resource for learning about how the 1998 OBD2 system operates. Specifically, page 4:
http://www.motorcraftservice.com/vdirs/diagnostics/pdf/obdsm986.pdf

 

[white_shadow]

The rear o2 sensor essentially measures the efficiency of the catalytic converter. By comparing the output of the rear sensor to that of the front sensor, the computer is able to determine the catalyst's efficiency.

If the rear oxygen sensor goes out of a predetermined range, the computer will store either a catalyst efficiency trouble code, or one related to the circuit/shorts.

Here is a great resource for learning about how the 1998 OBD2 system operates. Specifically, page 4:
http://www.motorcraftservice.com/vdirs/diagnostics/pdf/obdsm986.pdf

thanks, ill check out the link. so basically, the rear o2 is just measuring how well the first cat is doing its job? reason being, im getting a p0430 ( iirc ) code, and i cant pass inspection, and im not buying new cats for a 15 yo explorer. just need it to pass inspection, truck runs like a champ, other than the CEL being on. im wondering if i just unscrew the o2 and let it see fresh air while i plug the bung, will it make the computer happy enough to let me pass inspection? im getting 3 not readies, egr, catalyst and evap. i can only have 2 to pass inspection.

edit: the truck keep the 3 not readies after almost 100 miles of driving with several restarts.

 

[thorney_5]

Affirmative on your first question. I think checking out that link will really help you get those I/m readiness monitors complete. It tells what conditions must be met for the monitors to run, and what would cause them to fail. You can actually tailor your driving to enter the monitor cycle.if you don't have any other codes then that's all you really need to do, get the monitors to run and show the system is functioning properly.

There really isn't am easy way to get that rear 02 back in range without replacing the cat.

 

[white_shadow]

ugh, thanks for the info. was hoping for an simple fix. the bad cat is whats causing the CEL to come on, im getting the 0420/0430 code. so the egr and the evap being not ready are not turning on the CEL, so both first cats are bad, just priced them out and ouch.

as im reading through on the link, on page 3, it is saying the rear o2 may be deleted, do i interpret that as just unplug them and roll on or should i pull the o2 out and just let it see fresh air and plug the bung?

edit: i was thinking a 98 was OBD2?

 

[thorney_5]

The 1998 is OBD2. Where it says obd1, you should ignore. Vehicles over 8500 pounds did not have to comply with obd2 until the early 2000s. The chart simply states the differences that will be seen on the obd1 vehicles(not yours). You CAN NOT simply delete the rear o2 sensors in your application.

If your state allows 2 monitors to not be ready, and no other codes are set, you can still pass. Refer to pages 11-13 and page 22 to see details on the evap and egr monitors, respectively. If the PCM runs just one of these tests, you will pass emissions. The charts list minimum and maximum parameters for the tests to run.

 

[white_shadow]

The 1998 is OBD2. Where it says obd1, you should ignore. Vehicles over 8500 pounds did not have to comply with obd2 until the early 2000s. The chart simply states the differences that will be seen on the obd1 vehicles(not yours). You CAN NOT simply delete the rear o2 sensors in your application.

If your state allows 2 monitors to not be ready, and no other codes are set, you can still pass. Refer to pages 11-13 and page 22 to see details on the evap and egr monitors, respectively. If the PCM runs just one of these tests, you will pass emissions. The charts list minimum and maximum parameters for the tests to run.

the only codes stored are 420/430, so its turning on the CEL, i think its time to jsut replace the cats. local parts house quoted me ~ 400 for new magnaflow cats. they have weld in universals for ~300, then i would need to take it to an exhaust shop to have the old ones cut out, and the new ones welded in. i think it would be cheaper in the long run to just get the magnaflow bolt in ones.

 

[masospaghetti]

You can try using a "spark plug non-fouler" to trick the aft o2 sensor. It essentially creates a dead space of gas in front of the sensor by backing it away from the exhaust stream. Illegal, but it does work.

I used it after I was still getting a code, AFTER replacing my cat with a new Magnaflow. This was on a Camaro.

 

[jremington59]

I'm first going to replace a sensor before assuming the cats are bad. Have you had it scanned while running to be sure the cats are bad?

 

[white_shadow]

I'm first going to replace a sensor before assuming the cats are bad. Have you had it scanned while running to be sure the cats are bad?

after i reset the computer, i have several not readies, as i drive it around various systems become ready, only the egr, evap and catalyst stay not ready, when the catalyst changes to ready, it triggers the CEL. my dad has a laptop with some program on it so we can watch live data from the rear o2's, going to get that done this weekend and go from there. im thinking if i can find the voltage the computer is looking for from the rear o2's, i can put a resistor inline, so that it reduces the voltage to what makes the computer happy. im still researching online though. my guess is this so far, too low voltage and to high voltage = CEL, im thinking im getting to much from the o2, so if i put a resistor inline, it will drop it to where the computer is happy. just a thought, the idea of replacing the cats is still on the back burner though. if i go the replacement route, i have found 2 options, a) get the magnaflow bolt ons, ~300 bones from local parts house, or b) buy just the cats themselves, take it all apart, cut out and weld in the new cats myself. i think i can do it for about half, but the PITA factor is higher. either way, i need to do something, truck is due for inspection now, and in my state ( nc ) you have to pass inspection to get new registration.

 

[white_shadow]

You can try using a "spark plug non-fouler" to trick the aft o2 sensor. It essentially creates a dead space of gas in front of the sensor by backing it away from the exhaust stream. Illegal, but it does work.

I used it after I was still getting a code, AFTER replacing my cat with a new Magnaflow. This was on a Camaro.

where would i order those from? ill just go ahead and get a set and try it, thats something i can pop in easily.

edit: i have never used these, do they go on the spark plug or do i put the o2 in it? dumb question, maybe, but since i have never used them. i read that that they go on the spark plugs, if thats the case then i dont understand how that would help me. i am not burning oil.

 

[jremington59]

So you're getting the code for both banks? By any chance is your exhaust in bad shape near the manifolds? If the sensors test fine a friend of mine told me he ran a rerod through the center of the cats and it worked for clearing the codes. I don't know if it works though. Have you checked Rock Auto or any other online places for the cats if you do have to go that route?

 

[white_shadow]

So you're getting the code for both banks? By any chance is your exhaust in bad shape near the manifolds? If the sensors test fine a friend of mine told me he ran a rerod through the center of the cats and it worked for clearing the codes. I don't know if it works though. Have you checked Rock Auto or any other online places for the cats if you do have to go that route?

exhaust is in good condition, its a southern truck so salt is not a serious issue here ( nc ). ill know exactly what the rear o2's are saying this weekend when i get a chance to hook it all up to the computer.