02 Sensor? Fuel Filter? (vida dice data included)

[draser]

Based on these tests looks like both sensors are toast, and the cat. The recovery time should be millisecs not minutes. They're supposed to cross over at least once per sec. If the cat works, the post cat sensor has nothing to do, there should be minimal crossings. The other thing is that the system (sensors and ECU) never got to closed loop mode, where they cross happilly back and forth. Looks like, from your voltage readings, that Volvo uses a DC component to shift the normal 0.1-0.9VDC sensor output, that's why you have these high readings. They use this component to tell the ECU there's a sensor problem when they do not crossover. Can you actually graph the O2 sensor signal versus time?

[carboncow]

Based on these tests looks like both sensors are toast, and the cat. The recovery time should be millisecs not minutes. They're supposed to cross over at least once per sec. If the cat works, the post cat sensor has nothing to do, there should be minimal crossings. The other thing is that the system (sensors and ECU) never got to closed loop mode, where they cross happilly back and forth. Looks like, from your voltage readings, that Volvo uses a DC component to shift the normal 0.1-0.9VDC sensor output, that's why you have these high readings. They use this component to tell the ECU there's a sensor problem when they do not crossover. Can you actually graph the O2 sensor signal versus time?

Looks like you know your way around 02 sensors...and I know Jimmy does to specifically for Volvo.

1. What makes you think the cat could be jacked too?
2. I have some graphs in this post that show the 02 values as a function of time. Could you specifically let me know what "signal" you are looking and did you mean versus (opposed?) to time or as a function of time?

I think I may just order the front one per Jimmy and retest and see what we get since he said the rears values can be a function of the fronts values.

[jimmy57]

The ECM uses the front sensor for primary fuel trim so the CC will get the correct gas mixture with the proper fractions of component gases so the CC can do its job. When the CC does its job there is just a little oxygen left in the exiting exhaust gas and you get a rear O2 reading that is similar to a slightly rich sensor reading if it were a front sensor. The ECM can also, and does in many cases, use the rear sensor to fine tune the fuel trim a bit more so the CC has a longer life and works at its optimal performance. When the front sensor is biased the ECM will have the fuel trim off the correct level a bit and the rear sensor will not have the right signal and the result will be catalyst efficiency codes. The ECM has diagnostics for O2 sensor but many sensors get "lazy" and stay just inside the area where diagnostics do not flag a bad senosr so the sensor is assumed OK and CC is flagged faulty. Testing front O2 sensor is the first step to see if its response is timely and accurate. The front sensor should have had a greater range response than it did. The rear O2 response and range was OK.
The leak at the booster hose should have been ample to produce a very lean condition and the sensor should have driven fuel trim very rich to compensate.
Shawn,
I assume the car ran very ragged when the leak was uncapped. Did it completely smooth out after a couple of minutes or improved with some roughness still present?

The front sensor on Volvos for more than 10 years have (started with 99 model year) changed to linear type sensor where the out put signal is not a voltage. The signal is reverse of what the value is for voltaic sensors.

[carboncow]

Jimmy,

I believe it did "smooth out" to a level equal to the removal of the hose...with the exception that the idle went up a few hundreds RPMs (I believe).

I clipped the one graph to show again how the values were looking after about 1-2 minutes with the hose off and the system settled down. As mentioned before it was rough for the first minute as I swore the car would stall but I think we could call it settled.

On another note do you recall how many "pins" are on the front 02 sensor connection? While researching bosch replacements (cheaper then OEM which is most likely bosch, right?) I'm looking at ones that have the connector (not generic and thus need clipped) but I've seen both 4 and 5 pin connectors listed with some vendors!

Skitch.jpg (19.58 KiB) Viewed 2107 times

[draser]

I've seen these Vida graphs where they have O2 voltage on Y and time on X axxes, and you can see the sinusoid type graph, how many times a sec it crosses the X and what voltage you have. There was one for each sensor. The post cat sensor should cross the X axxis less because of the cat function. The ECU calculates cat efficiency based on number of crossing differential between pre and post cat sensors. So if they cross about the same the ECU thinks the cat is bad.

[jimmy57]

What you are saying is correct if the load is the same and fuel trim is functioning properly and is within acceptable range.
If the load is high the fuel trim is inhibited and the functioning of catalysts is unimportant.
The graphs showing oscillation of both sensors coinciding would be due to the catalysts not functioning and the gases not being processed. At steady load when the ECM is monitoring catalysts function there should not be any crossing of the center range of rear sensor as catalysts should be processing gases to the least harmful gases with a touch of oxygen leftover.
If the graph is at idle and A/C goes on/off or with a/c off the cooling fan goes on/off the load changes from those events will make the rear momentarily mimic the front. If engine is fully warmed up in closed loop and you watch the period when no load changes while idling the rear will stay in a narrow range .65-.75 V. IF front sensor is a bit slow to respond then the rear will drift to a signal that goes above and below 0.5 V like a conventional voltaic front sensor since the catalyst has periods of no function.

[carboncow]

Jimmy,

Got a few more pressing items fixed on the cars so I'm going back to the 02 sensor discussion you were helping me with here...

Our 2001 V70 is finally throwing an 02 code, specifically ECM-4801.

Based on discussion before you were guessing the front O2 was to blame...does this code confirm either the front or back?

This part of Vida confused me:

Substitute value
Rear heated oxygen sensor (HO2S) control is disabled.

This started about a month ago and is very intermittent...additionally since then the #2 cylinder is also stating ECM 3310. Not sure if a bad coil could coil could toss off the 02 value...but again the 02 error was showing up weeks before the #2 CSC did.

Shawn