Non-73-87 related - 99 S10 - no after cat O2 sensor...what does that cause?

[AJMBLAZER]

My buddy's dad has a '99 S10 pickup. 4cyl, auto, single cab, shortbed 2wd. Plain jane, used to be a meter reader vehicle. Like his son he neglects it to death but unfortunately is one of those older guys who uses stuff he "learned" 30+ years ago about cars with newer tech.

At some point...for some reason...the cat was removed along with most of the pipe up to the flange as well and it all was replaced with flex pipe. He was complaining it's gotten loud so I was looking at it and realized...there's no 2nd O2 sensor. The one that should be after the cat. Someone just unplugged it from the harness and tucked the harness up against the trans. It's not there at all.

Yes, his check engine light is always on.

He doesn't drive it long distances usually and well, he's an old guy that is sort of a painter and handyman so normally it just goes to the bar and/or various jobs. It was so in need of a tune up...ugh...we put new plugs and wires in, it has a newish fuel filter, oil change, air filter, etc and it still runs rough.

Would the lack of an o2 sensor cause it to go into "limp home mode" and not run correctly? Doesn't even sound like a miss or a ping, just not running right.
When my '96 Ranger had 140,000 miles on the original plugs and wires and the smallest gap was over .075 and the largest past .1 it ran better than this thing does now with all the new tune up parts.

 

[sweetk30]

check engine light = on

o2 after cat checks efficence of cat. make sure it working just fine.

2 ways to dump it.

o2 simulator plug in.

or

full reprogram / flash of computer to turn it off.


why do you ask today ?

 

[AJMBLAZER]

What does the computer do since it isn't getting any signal from the o2 sensor?

 

[K85 Octane]

normally just throw a code to say it's not sensing an O2 and/or cat. The front one measures F/A ratio. Someone needs to put the cat and sensor back on. The crapping performance is likely from something else. If it's louder, sounds like it's running rich.

 

[sweetk30]

What does the computer do since it isn't getting any signal from the o2 sensor?

like i said in my first post here. check engine light on .

 

[4xcrazy]

i will 2nd what others have said already, the after-cat sensor is just to detect if the cat is working properly or not.

I just went through this with my dads car a few months back, the cat had somehow blown out the insides, making it hollow from a poor running condition, making it run very rich. It kept throwing the check engine light on until eventually i found another cat for this vehicle, installed it and all has been good since.

Reason it had to be done, as even though it doesn't affect engine performance, Arizona emissions stations wouldn't pass it due to this CEL condition, and lack of properly working cat.

the running rough is something else, possibly weak fuel pressure, have ya checked that yet? vacuum leaks?

 

[AJMBLAZER]

What I'm getting at is along with the CEL coming on does it make the engine go in limp home mode or something?

Guess not.

Frankly I'm not too worried about it. I'll help when he's asking but until then well, it's not my problem. Sad part is his son feels about the same way since he doesn't listen to any of us. Got all that "knowledge" of cars back in the 70's ya know.
Guy's had it for years and only had one set of keys because he was convinced that since the factory keys had plastic heads they must be chipped keys and would cost tons to get new ones made. Never asked anyone though. Coulda had new ones made at Ace for $5.
Lost his keys and locked himself out of it a few weeks ago a few hours south of here. Ended up dragging my buddy down there the next day and instead of having the local GM dealership cut him a new door and ignition key he cheaped out and smashed a side window and then drove it home.
He was then surprised when the cost of a new junkyard side window wasn't $10.

The guy's a good guy but oy.

like i said in my first post here. check engine light on .

Right, because your first post was soooo clear and well written.

 

[K85 Octane]

If it's running rich, idling funny, and you have already changed everything known to man......

fuel injection spider, maybe, not sure
notorious on the 4.3's anyway

but it's amazing what plugs, wires, cap, rotor, O2 sensors, and some SeaFoam can do.

 

[AJMBLAZER]

It's a 4cyl and all the usual stuff has been replaced. No distributor or cap obviously. My buddy talked about SeaFoaming it but who knows if they will do it?

Like I said, they need to let me know if they want to do anything else. I was mainly just curious about the O2 sensor.

 

[6.2Blazer]

Just to agree with the above, removing the rear O2 sensor and/or cat should only set the check engine light and cause no changes in how the engine runs. There is only one CEL, but there could be more than one code causing the CEL.....tell them to spend 5 minutes at the local auto parts store and put the scanner on the truck to see what codes.

The other red flag is the comment about the exhaust getting loud and the cobbled flex pipe. A leak in the exhaust around the forward O2 sensor will give it a bad reading and make the engine think it's running lean.