O2 Sensor Help

[tc197]

Hi guys,

87 GMC V2500 350 TBI

My truck has been running rough lately and stalling at idle. I finally got around checking the DTC codes with a paper clip and found codes 13, 34, and 44.

Given that code 34 is MAP I replaced the MAP sensor and my truck ran a heck of a lot better. I don't stall at idle anymore, it starts better, and idles smoother. Also after replacing the MAP sensor the truck began backfiring out of the exhaust when hard engine breaking. The first time it happened I thought someone had a shotgun in the bed. I figured this might be due to the codes 13 and 44 now which are both o2 sensor related.

Now I have a couple of questions:

1. What is the difference between code 13 and 44? Does the fact that both appear mean more or less than just one or the other?

2. When I recheck the codes now, 34 still appears even though I changed the MAP sensor. Do I need to clear this or something for it to go away?

3. I purchased a new o2 sensor to see if it will help with the 13/44 codes but it looks like I have 2 o2 sensors? Everything I read on here says I should have 1 o2 sensor on the drivers side manifold, but I also have something that looks just like an o2 sensor at the Y-pipe in the exhaust. Is this normal and do I therefore need to replace both sensors?

4. When I do go to replace the o2 sensors, whoever previously installed the sensors appears to have cut and spliced wires. Should I buy a connector to mate up with the connector on the new o2 sensor or just go ahead and cut the new connector off and splice it into the harness like was done previously?

Thanks for any info, I've been searching for awhile now and haven't found anything yet.

[VileZambonie]

Post pics. Sounds like someone added one.

Have you checked for vacuum leaks?

[tc197]

Here are the two sensors. Y-pipe next to the trans and manifold near the oil filter. I checked for vacuum leaks by spraying carb cleaner about a month ago but not since replacing the MAP sensor yesterday.

[tc197]

Any thoughts on the code 13 vs code 44? Also, if someone had added a second sensor, how would they wire both in? I'm assuming there is only 1 spot in the harness for the single o2 sensor?

[ehjorten]

Well Code 13 is an open circuit in the O2 sensor and Code 44 is a low voltage in the O2 Sensor...so...could be a bad o2 sensor or it could be faulty wiring to the O2 sensor.  O2 sensors are not designed to last for life...they do wear out and yours look pretty crusty...I would start by replacing it, simply because it is more than likely time to replace it.  If that doesn't fix it, then I would look to the wiring of the sensor to see if something is chaffed or a bad connection.

You could have an exhaust leak, low fuel pressure, and/or vacuum leaks.

I don't know what the story is with the 2 o2 sensors!

[tc197]

Definitely replacing the o2 sensor, I was just hoping to sort out the double sensor issue. I could replace both but if one isn't even doing anything why bother.

[VileZambonie]

You'll have to follow the wire and see where it is going. Maybe someone was trying to remedy a problem with a hack...