'93 5.8L


It seems for the KOEO codes, I get a 111, and another 111. System pass. Then a long pause, one beep, another long pause, then code 172, right side O2 sensor shows lean.

I didn't know this truck had 2 O2 sensors, I only ever noticed one when I've been under there. Since there apparently are, which one is the "right"? It's a single pipe, so I'm unclear about a "right" as opposed to a "left".

Does this mean an actual problem, or is the sensor just bad and in need of replacement?

I couldn't believe how rare OBDI(or whatever the 80-95 ones are called) scanners are, I finally tracked down an AutoZone that had one for a whopping $19. Not a single shop nearby had one, and none of the auto stores I frequent did either.

 

I think the description may be a bit incomplete. Here is a description I found at: http://www.freeautomechanic.com/diag...blecodes7.html

172 (R,M) Oxygen sensor not switching - system is or was lean - Single, Right or Rear HO2S - Fuel control

I've grown to have faith in the fault codes - they're right much more often than I am. If the sensor wiring is intact and undamaged, then I would say chances are way better than average that the sensor is out of spec. If I read the code right - it's saying that the O2 reading isn't changing when, in fact, it should be.

If the computer had adjusted the fuel flow to one of its limits based on this sensor feedback, that should be another code.

Unfortunately, you're probably going to pay a bit more than a 'whopping $19' for a new sensor :-)~ More on the order of $40-$60.

 

Nah, meant I paid $19 for the code reader....As I found out today, a O2 sensor for the truck runs me $53. I didn't buy it yet, since the guy at the store suggested that I pull the connector off and clean it, since apparently corroded connectors often trip O2 sensor codes.

It's not surprising the code is vague, the whole manual was a little unclear, and also in 4 languages.

So "single, right, or rear" would refer to the downstream sensor, the one after the cat/con?

 

I think the after-cat sensor would be the one. Checked back on the site the first code came off of - it appears code 176 would be the corresponding fault for the before-cat sensor:

176 (M) Oxygen sensor not switching - system is or was lean Left or Front HO2S - Fuel control

Never have had problems with corroded O2 sensors - usually have that di-electric goop in the pins, but I suppose if there's a chance it could save $53 - go for it.

Be sure the exhaust pipe is cold to avoid burring up the threads. I made that mistake once, and now every sensor replacement becomes a self-tapping thread exercise.

 

Here's the thing, it doesn't have an after-cat sensor. The exhaust is highly visible, and I didn't see one after either the first or second cat. The first is at the merger of the left/right headers, right between the two. Couldn't find a second one anywhere.

The sensor looks like it's been replaced at some point, it's not as...dirty as the stuff around it. The terminals are wires look fine, and there was that electric grease on the pins.

So unless I was looking in the wrong place and totally missed the downstream one, it seems I only have one.

 

Looking at the 172 code description - it does include the term 'single' - so you may only have one sensor. Remember these codes were set up to include a wide range of vehicles, not necessarily just F150s.

If I understand your description, I think what you're calling the first converter is actually just a collector - has 2 inlets and one outlet. Not aware of putting two converters inline on these models. There is a cross-over pipe connection between the two headers before they enter the 'collector', which contains the O2 sensor.

Being a '93, I doubt it's the original sensor. I typically get an O2 sensor fault code every 5 years or so.

 

There is a cross-over pipe connection between the two headers before they enter the 'collector', which contains the O2 sensor.

That's exactly where it is, and I suppose you're right in that the codebook's vagueness was to cover as many vehicles as possible.

Thanks for the help, I'll pick up a new one tomorrow.