Pre Cat Lambda Sensors.

[Gloomy]

Hi, have been offline for awhile, working in the States. My problem is as I have returned from the States, my first port of call was my Z4MR 2006. Car is now running very lumpy, missing and popping back through the exhausts. I have taken some real time data readings. Ready
Signal, Oxygen sensor before Cat. Conv, Bank 1 voltage 1.9 to 2.0 volts
Signal, Oxygen sensor before Cat. Conv, Bank 2 voltage 1.7 to 2.0 volts
Signal, Oxygen sensor post Cat. Conv, Bank 1 voltage 0.0 volts
Signal, Oxygen sensor post Cat. Conv, Bank 2 voltage 0.7 volts

Plugs all look to be running slightly lean.
Bearing in mind on the Pre Cat sensor's the sweet spot is 0.45 volts, and the voltage readings should not fall below 0.1 and not rise above 0.9 volts. The high voltage readings on the Pre Cat sensors indicate the engine is running very rich, but the plugs say different.
Would I be right in thinking that the 2 Pre Cat sensor's are no longer working.
Car has failed it's MOT emissions test.

Any input from you guys will be much appreciated.
Many Thanks in advance, Gloomy.

 

[andyfanshawe]

Hi Gloomy.
What did you use to get these readings? The before cat sensors dont look right at all.
What was short and long term fuel trim readings?

How long has this been standing?
Oxygen sensors are tested by pushing them rich and seeing if they respond. I just blip the throttle and watch for an increase in voltage from both pre and post cat. Or. if the car is reading rich to start with, pull off a vacuum pipe (servo a possibility on most engines) to lean it out and watch for a corresponding drop in pre and post cat sensors again.

Popping in the exhaust is usually a rich mixture, popping in intake is usually an indicator of a lean situation.

Let me know what scanner you used.
And try to warm it up a bit and see what the short and long term readings are doing.
Oh, check the scanner says it is going into closed loop.
Whereabouts are you in the UK?

Bit jealous about the states bit! No, a lot jealous actually!
Andy.

 

[andyfanshawe]

Just looking at this again.
Really difficult to give a direction when I cant hear the engine. But...
Get me some fault codes please.
Assuming the pre cat sensor readings are correct and fixed high and rich (and i dont think they are because the post cat sensor readings dont show that), the short term and long term fuel trims should be waaaay negative and pulling fuel away. Which might explain the white spark plugs.
Get it running, and tell me what the short and long term trims are doing. Essential.

Andy. 07833 967239

 

[Gloomy]

The OBD2 reader I'm using is a Delphi DS150E. Initially there was a fault code for Post Cat sensor can't remember exact code then car failed emissions test. Checked K&N filter quite dirty, cleaned and re oiled. Filter allowed to tack up for 2 days before refitting. Car then brought up to temperature, all real time data taken at idle. Fault codes, 2C7F, 29D0, 29D1 and 29D2. Car has stood for 6 weeks, but engine has been run regularly. Cheers.
P.S. Will do some testing at 2500rpm.

 

[andyfanshawe]

Thanks.
Get me short term and long term fuel trims at idle AND at 2500 rpm.

Codes are oxygen sensor bank 2 sensor 2 - trim control
Then cylinders 4, 5 and 6 misfires. Which is undoubtedly bank 2 also.

Still worried about the very high pre cat o2 sensor voltage readings though. Can only be feeding in from the heater circuit via the loom or the internals of the sensors. Quite interesting that both pre cat sensors are reading high though. But will wait for trims.

May be asking you to unplug the pre cat sensors and tell me that voltage again.

You haven't got mice and/or other critters near the car have you? Nibbled wires???? Lol! Just a thought.

Any other history of work on the car that may be relevant?
When did this start?
Was it running okay the last time you drove it?

Andy.

 

[Gloomy]

Hi Andy,
I have attached the info I believe you asked for, I should like to admit that once into Delphi I was a bit out of my depth. See what you can make of it.Thanks in advance. Gloomy.