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[Peter13]

Hi Guys!

Last year I was getting the MIL blinking sometimes, then more and more frequently. When it came always during moderate accelerations on highway, I replaced the lambda sensors. Replacement came from ebay called "Vauxhall Frontera Omega LAMBDA OXYGEN SENSOR - 90509274"
It was not original Bosch 90509274.
Then the fault kept coming. Okay, I had had a replacement ECU, I put it in. Same issue. There were problems with my head gasket, I replaced it a month ago and did a full head renewal at shop.

Current status:
Engine is running smooth and fine, but I have the MIL permanently on, however the car has just passed the emission test with outstanding results. (its results also fit the euro4 standard!)

Paperclip test shows 13 and 89, which should mean both my lambda sensors are open circuit. I have checked yesterday, they are connected and fitted well.
(before the head removal sensor 2 went to open circuit sometimes during acceleration, and I am afraid I may have broken the cable for sensor 1 during the head job, but this is too much I think)

Finally the question: can I do anything else to diagnose this issue than buying new sensors again?

[cem_devecioglu]

you can measure the voltages at connections and impedance of lambda sensors and if possible find someone with tech 2 and monitor them..

http://www.picoauto.com/applications/lambda-sensor.html

ps: using ohmmeter on some lambda sensors may create problem so please read the link ..

[Peter13]

News:

I have checked the voltages using an "My Naff Code Reader".
One sensor is quite okay, close to 450mV when idling.
The other shows 20-50mV during idle, and can go up to 900+mV when reving up. This is weird.

Another thing that the fault shows signs of disappearing:
After the maintenance work MIL started to lit permanently. On the way to home at the weekend it went out sometimes, on the way back today MIL came to on only sometimes. ?

I am about to record data of a whole drive.

[Kevin Wood]

Both lambda sensors should be cycling between <200mV and >800mV all the time at idle and under light load if they are working properly. 

[Peter13]

Latest new on this:
I have replaced one of the sensors (left side, passenger's side for you - driver's here), which seemed more often to go open loop.
A few miles after, on the way from the shop to the office the MIL light went off, but if I looked to the laptop on the seat near I saw the read signal value is still low and stable when I was stopped at trafficlights. It was okay when the car was moving.

I will upload the before and after logs from my "My Naff Code Reader" in the evening.

[robmac]

possible air leak maybe in exhaust/manifold on that side???

[Peter13]

I am starting to assume the same..., but no strange/thicking noise, no visible sign of a leak on the exhaust manifold.
How could I get evidence of an exhaust leaking?

[cem_devecioglu]

I am starting to assume the same..., but no strange/thicking noise, no visible sign of a leak on the exhaust manifold.
How could I get evidence of an exhaust leaking?

you will smell unburnt fuel from the car (car revved a bit and you are outside) as the mixture gets richer.. and the consumption a tad higher than  usual..
 
 
 
 
 
 
 
 
 
 

[Peter13]

Nothing like this for fortune.
I have downloaded now the logs of today. One on the way to the shop, second from the office to home.
Findings: originally I have very often had both my oxygen sensors in open loop together. (from line #2700 in before xls)
After replacing the left (passenger's side in UK) sensor, I see sometimes only the Loop1 to go open. This is strange cos I believed sensor 1 is on the left and sensor two belongs to the right. However this is contradictional to the fact, that the pistone #1 is on the rdriver's side(right). (see from line #1160 in the after xls)
I do still have the low but closed loop state radings when idling.

Does this mean sensor replacement did the job and I should replace the other one as well?

http://landboyz.4step.hu/20111010_before_2.xls
http://landboyz.4step.hu/20111010_after_left_o2_sensor_2.xls

[Peter13]

Hi All!

I think I am on the way to figure out this.
When I check the lambda signals in idle they show very lean mixture (<100mV). Then I tried to disconnect the MAF sensor and voila, both lambda voltage started to alternate between 150mV and 900mV!
Now I assume that will be a vacuum leak or my MAP sensor is gone. (no fault code yet for it. live data seems okay)

Another concern is the ignition timing. Is that normal that I see almost always the knock signal inactive in logs? And knock retard at ZERO?
You can check in the xls linked above.

What is the normal spark angle in idle?

[Kevin Wood]

When I check the lambda signals in idle they show very lean mixture (<100mV). Then I tried to disconnect the MAF sensor and voila, both lambda voltage started to alternate between 150mV and 900mV!
Now I assume that will be a vacuum leak or my MAP sensor is gone. (no fault code yet for it. live data seems okay)

Hmm. MAP sensor problem perhaps?

Another concern is the ignition timing. Is that normal that I see almost always the knock signal inactive in logs? And knock retard at ZERO?
You can check in the xls linked above.

That's exactly what you want to see. Knock signal should stay inactive. If not, it starts retarding the ignition to save the engine.

What is the normal spark angle in idle?

It varies widely at idle as it's used by the ECU to stabilise the idle speed. I'd say anywhere between a few degrees negative and about +12.

[Kevin Wood]

Oh, and as you sit in the car, sensor 1 is on the right. On the same bank as cylinder 1. So, bank 2 has improved and bank 2 is the sensor you swapped, IIRC? Maybe it was just tired lambda sensors?

Disconnecting the MAF probably forces the system into closed loop, since there is no load input available, that's the best approximation the ECU can make, so the Lambdas will start toggling regardless of the amount of fuel trim required.

[Peter13]

Oh, and as you sit in the car, sensor 1 is on the right. On the same bank as cylinder 1. So, bank 2 has improved and bank 2 is the sensor you swapped, IIRC? Maybe it was just tired lambda sensors?

According to my available documentation states the sensor 1 is on the left side, despite the piston1 is on the right. I don't think this is because I drive an opel.
This doesn't matter because it seems any of them can go to open loop and very lean before.

Disconnecting the MAF probably forces the system into closed loop, since there is no load input available, that's the best approximation the ECU can make, so the Lambdas will start toggling regardless of the amount of fuel trim required.

As far as I know the sensor voltage can be substituted only to 450mV by the ECU when it can not read the signal voltage or it is out of range. So I'm happy with my working sensors (now I have 4 of them )

[Kevin Wood]

As far as I know the sensor voltage can be substituted only to 450mV by the ECU when it can not read the signal voltage or it is out of range. So I'm happy with my working sensors (now I have 4 of them )

I think the ECU is more intelligent when the MAF sensor fails. The car would no be remotely drivable with a basic substitution but in practice it's not too bad.

[Peter13]

I am going to replace the MAF today in the evening and will do air leak tests as well... Will report back tomorrow!