Presumeably such an exhaust leak leak would have to be BEFORE the sensor(s)? i.e at the header?

 

Correct. You say you do have graphing, do you see why? A voltmeter will simply give you an averaging, so your .5 volts could actually be good.
A lot of work to rule out the O2 sensor. Fuel pressure ok?

 

So, some further investigating. The graphs are a little inconclusive - possibly because they're taken during the warm up period.

However, I then unplugged the upstream sensor and went for a little drive agin from cold. What I found was improved idling, no stumbling, no dying when coming to a stop. There may have been a decrease in power delivery it a higher rev range (around 3000rpm).

Here's the graph from the cold startup, just after PCM goes into closed loop mode:



It might not tell much as the engine wasn't fully warm at the time. - for that, I will have to plug the sensor back in, and I don't fancy crawling under the car again today as it is wet out.

A minute or two later the voltage continued to decrease in the same pattern from around 0.74 to 0.64

I am, at present, unable to test fuel pressure

 

Hm. Well kind of hard to read the horizontal scale but try increasing it to 1-5 seconds...However, if that is one half cycle, and the lowest it gets to is .84ish, indeed, that sensor looks hosed to me. You DO have to be all the way hot though, try taking it for a drive first, that said, I have never seen a good one get up beyond .9 ish...even cold...and you're nowhere near .1.....Another thing these are famous for is the wiring harness shorting out by rubbing on the manifold or frame somewhere so make sure that isn't the problem either, but I think you may be on to something if your voltage from that tool is accurate..

 

The graph is taken over a 30 second period, so what you're seeing is a gradual decrease in voltage over that period. If it does normalise after the engine warms up am I looking at a heater circuit issue? I'm not sure how to test this.

That said, unplugging did seem to pretty much resolve all the related issues of poor idle, stalling and bucking.

Again I can't see any damaged or frayed wires from the upstream sensor.

 

I must say that this had been a model thread as to how to properly ask for help. It's certainly a breathe of fresh air versus the copious amount of "HELP!!" threads that get started but the OP won't don't any actual testing themselves. Thank you Jord!

 

LOL Jeepin, right on.

Well, Jord, if that period is 30s fully warmed up, then I would have to suspect that sensor is kaput.
That said, I think you can check the sensor ground at the plug, maybe somebody else can weigh in here, but it should be a 4 wire sensor, 2 are for the heater should be +12 and ground, then the sensor input then another ground for the sensor. Be very careful here...if you get the meter setting on ohms instead of volts, you run the risk of hurting the pcm.
Also just poking the probe inside the little plug you could short the +12 to the sensor input and hose the pcm.
I'm not too comfortable advising you to poke around like that, so, I would think the next step is either replace the sensor or some bench testing of it.
I would add that on my Actron, the graph is textbook, swings from .1 to .9 about 1 time a second, (not sure if thats right, think it should maybe be faster) even cold, or maybe the heater heats it up so quick its already hot.

 

It's 30s in closed loop, not necessarily fully warmed (i.e. car had been idling for about 2 mins from a stone cold start)

I'm not gonna risk prodding with my multimeter. Off for another unplugged run, then will re attach sensor and take voltage reading at full temp.

 

So finally, run to full temp (8+ miles at a range of speeds) did this with sensor unplugged and it ran/idles okay.

Plugged sensor back in for full temp reading and got this:



Another 30 second sample. To me this could read as either a rich condition or a bad sensor(!)

Having unplugged the sensor, I also got code P0132 O2 sensor circuit high voltage. I cleared the code, but even with the sensor plugged back in it comes back at each start up and as a result is unable to run in closed loop - not necessarily a bad thing at the moment given it runs better like that - but obviously needs sorting soon.

 

Ok, it appears to me that is the classic bad sensor, not heating for one, and a classic fail "stuck in midrange" mode.
One thing, you keep mentioning closed loop, how are you surmising you are in closed loop? I don't doubt that you probably are after 8 miles. To my knowledge, the CTS has to be at or over 190F reading and at least the 02 monitors have to be run, not showing incomplete. Just curious, not likely affecting what you are seeing with the sensor.

 

The scan app shows if it is running open or closed and closed loop comes on way before 190 (coolant temperature also shown by scan app - not going off the gauge on instrument panel)

I guess I'll change the sensor and if things improve I'll keep battling away with the other niggles wit the machine. If things don't improve - might be time to weigh it in!

 

Sounds pretty reasonable. Be sure to get the one mentioned...nkg>? Let us know how it goes be interested to know. The monitors are the obd2 monitors, does the tool show the status of those?

 

The usual suspects (Autozone, et al) will 'rent' you the tool for free. You 'buy' the tool at full price, take it back within 90 days, and they give you a full refund. This way they don't have to mess with rental agreements, deposits, and that nonsense, and they hope you will buy parts when you bring it back.


Agreed!!!!

This has been great! I'm learning stuff!

 

Yeah, hate to think this is just an engine starving for fuel. Worst thing you can do, run lean, next to no oil or coolant lol.

 

Pretty much nailed it that it's a bad O2 sensor. The total lack of waveform is a dead giveaway. A natural rich condition from some other would be evident without the O2's input, as one of the O2 sensors jobs is to help the PCM from preventing running rich.

Closed loop is something low like 130 or 150°F, surprisingly.