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jeff_hooper

Oxygen sensors

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Road tested my 96 V8 tonight with laptop recording data - Gendan software.. I suspected a problem - I've been getting some popping on tickover for the last 1,000 miles and now have an occasional problem getting no boost when applying steadily increased throttle in lower gear, the car seems to hesitate and hold back (like an old carburetor did when cold with not enough choke) feels liek the fuel is going in but the engien just isn't picking up then Whallop! boost seems to kicking in with a thump in the back, no build up just all at once!

1. On three of my O2 sensors i'm getting variable readings within limits which will probably draw as curves if graphed out - so I guess they are okay. But on Oxygen Sensor 2 Bank 2 I'm getting 0.49 V all the time - with no changes.. I'm guessing this might indicate a knackered LH Bank Cat? Although its throwing no fault codes..... - Yet..!?

2. I'm guessing, 'intake manifold pressure,' is my best option for assessing boost? any ideas what sort of reading are within parameters? Or is there some other reading I should be looking at to assess boost pressures?

Thanks.

Jeff H

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Hi Jeff sorry I cant help at the moment but let us know what you find out when all sorted. I would give you some live data from my EZ Scan 4000 Scanner to compare notes but one of my newly replaced left bank sensors is still bringing up same check engine code, so im not going to give you data incase mine isnt right either :welcome: Let us know how you get on.


350.gifNo.23

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The symboms you describe indicate a problem with one or both of the pre-cat (that's bank one, sensor one and bank two sensor two) sensors.

The pre-cat sensors should be oscillating between approx 0.15v and 0.85v. At idle you should get a full oscillation every few seconds but it will be quite jerky and not always a clean sweap up and down so it's hard to tell whether there's a problem with the sensor.

But as you increase the revs, the oscillations will speed up dramatically and become very jagged, literally straight up and down. It you don't see that there's probably a problem with that sensor.

The post-car sensors are a bit of a grey area. They's supposed to indicate a potential problem with the catalysts, but there are other factors which can affect them. It is RH one a steady 0.49v with no movement? Is the LH oscillating the same as a normal pre-cat sensor or is it slower or with a lower amplitude?

Regarding boost, yes you want to look MAP sensor. At idle it should be around 0.35 bar, increasing as you accelerate the car. At full throttle in fifth gear with the turbos spinned up you should see approx 1.75 bar.

Edited by neal

May: DON'T hit it with a hammer!

Clarkson: Why?

May: Cause it's the tool of a pikey.

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I didn't think post cat 02 sensors were utilised on UK cars? I know they need to be plugged in, but thought they were ignored by a UK ECU?

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Jeff,

O2 sensors should give a reading between 0.1v (lean) and 0.9v (rich). However, as Graham pointed out the UK cars don't act on the post cat sensors. They just check that they are connected.

Have you taken a trace of the MAP yet? If you do please feel free to send the file to me and I'll look and compare against results from my V8. Can you please monitor MAT, RPM & Speed as well as the MAT. I'll pm you my email address.

Regards,

Peter.

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Certainly on UK cars the post-cat sensors aren't used to monitor the performance of the catalysts.

However, I'm not sure whether they need to be connected. On my car they aren't and that doesn't cause any problems or CELs but it does have the S350 code. That said they're not completely ignored. I was a bit perplexed a while ago when I started getting a CEL indicating a high sensor voltage from a missing sensor! A disconnected sensor should give a steady 0.49v. It turned out to be a short in the engine wiring harness between the sensor output and the sensor heater.


May: DON'T hit it with a hammer!

Clarkson: Why?

May: Cause it's the tool of a pikey.

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Jeff, you can change the sensors (if they not fully rustet..) from front to rear. OK -the rear sensors are not needed for detections in European/UK cars, but they work also . And you can compare the readings before and after.

Only problem is the rust! So let your car cool down -and then use an gas welder or similar and heat up the ring section in what the sensor is screwed in. This should give you the possibility to move/turn it slowly in the treats.


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to name the things if I see them, that's what I call integrity..

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