Quick code question

[jnrice]

Hey gang, I have come here many times to help trouble shoot my totally (except for my sweet custom bike rack in the back!) stock '99 Ranger w/ a 4.0L V6 as it always seems to have something that needs a little help. I've finally come across one that I can't figure out in my chiltons book and have found nothing that I trust on google so I figured I'd go to where the buck stops (here).

I have been chasing a miss for almost a year now and it has progressively gotten worse. I have been through with my multi meter and checked all of the O2 sensors, (cold, engine off as I can never get the running test to work with pins in the back of the wiring harness etc), MAF, TPS etc and it all checks out. However, the truck finally threw a code that wasn't just a generic "miss fire cylinder ?" and reported a bad sensor, a bad HO2 sensor. The truck has been running rich (based on the smell) and the code that it threw was "lack of HO2S1 -switches -lean (bank 2 sensor 1)". Their were also codes for misfires in cylinders 3, 4, and 6 and "System too lean" "System too rich". In other words, my truck is a bit of a sh!t show right now.

I have a few questions about what this actually means:

which of the three sensors are they talking about? At the price of O2 sensors I'd like to just replace it and see if that takes care of my problem.

are O2 sensors the sort of thing where I should consider replacing all three if one has gone bad?

is their any reason to not go with cheap OEM style sensors?

Thanks guys/gals always appreciate the help.

-The Newbie

 

[Earl43P]

The third O2 sensor (after the cat) won't affect how it runs. It simply monitors cat efficiency.

I suggest you clean the MAF and look for arcing plug wires (mist them with water at idle and revving, at night). The O2's may be telling the truth, but if they are originals, it can't hurt to replace the two upstream of the cat(s). Plugs, wires, coil are all suspects to look at. Examining the spark plugs themselves can shed light on the problem.

 

[snake]

How does it idle? The lean bank 1 and 2 is usually a code P0171 and P0174 and are pretty common. Check your PCV vacuum lines... they often get soft over the years, collapse and a hole rips in them causing a leak and throwing the code/s.

 

[adsm08]

Fix your misfires before replacing that O2 sensor.

Here is the catch, the OXYGEN sensors only monitor OXYGEN. They don't look at the levels of CO2 or fuel in the exhaust gas. A pair of dead misfires on bank 2 (which you have) will cause your O2 sensor code because if the fuel doesn't burn, it doesn't use the oxygen, and so it looks like a lean condition to the sensor. It ups the fuel to make the sensor switch, but the misfire means it doesn't, causing it to set a no-switch code.

Ohm out your coils, I think 3 and 6 are paired cylinders, which means that you may have a coil pack issue. Also, swapping your plug wires to the paired cylinder can show you if the coil is going bad. That is if you have access to a scanner that will show the power-balance.

 

[jnrice]

Thanks much.

Earl, The plugs and wires are less than 10,000 old and were all pulled and inspected about 5,000 mi ago when I started having this problem. I also checked the resistance across my coil pack and a new coil pack ad they were very similar (within 0.1 ohms) so i don't think that my spark is the issue. I cleaned the MAF yesterday and it did help to a little, but it has probably never been cleaned in the 100,000mi that the the truck has on it. I will go over my vacuum system today before I replace O2 sensors.

snake, the idle is occasionally effected by the miss but again nothing consistent enough that I cay say "my truck misses when ____________".

adsm, i was kind of working on the assumption that a bad signal from an O2 sensor would cause the computer to adjust the fuel/air ratio and make it run artificially rich, but I tend to be optimistic as I'd like to just have this project over with.

Oh, and the autoparts store has two different product numbers for the driver side and passenger side O2 sensor which seems strange to me. Can anyone confirm that they are all the same?

 

[adsm08]

Functionally the sensors are the same. I think the wires on them are different lengths though.