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      09-06-2019, 05:51 AM   #1
stevethresh
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Possible Failing O2 Sensor

I've just got hold of a OBDII scanner to read the engine fault that came up recently. App shows the code is a misfire on cylinder 4 so I'll start by replacing the ignition coil then spark plug.

While looking at the app I noticed the two O2 sensors don't behave when the car is revved. The attached image shows the readings as the engine speed drops back to idle. Could this be a failing sensor? (I confirmed the readings with mutiple apps).
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      09-06-2019, 04:11 PM   #2
therealdb1
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Rather than jump in and replace a single coil or plug why do you not swap them onto another cylinder and see if the misfire moves?
You say at present cylinder 4 is misfiring so swap that spark plug with cylinder 1 and swap cylinder 4 coil with cylinder 2.
Clear the cylinder 4 code and run the car again.
Depending where the misfire then occurs gives you more than a clue as to which part is faulty.
Of course, if the misfire stays on cylinder 4 you could be looking at an injector or something else but you will not have replaced a good plug and coil for no reason.

As for your lambda sensors you do not say which ones these are. I would expect you to have 4 on your car, 2 pre cat and 2 post cat.

The oscilloscope trace you show looks like one of each to me. Have a look at the other bank and see what they look like.

Last edited by therealdb1; 09-06-2019 at 04:24 PM..
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      09-08-2019, 02:20 PM   #3
stevethresh
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I swapped the ignition coils on 1+4 and the fault code followed the ignition coil so I've got a replacement being delivered tomorrow. The traces are from the same sensors just on bank 1 and bank 2. Not sure if they're before or after the cat. Before I think but I'll have another go after I've fitted the new coil.
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      09-08-2019, 02:29 PM   #4
Diawal91
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Quote:
Originally Posted by therealdb1 View Post
Rather than jump in and replace a single coil or plug why do you not swap them onto another cylinder and see if the misfire moves?
You say at present cylinder 4 is misfiring so swap that spark plug with cylinder 1 and swap cylinder 4 coil with cylinder 2.
Clear the cylinder 4 code and run the car again.
Depending where the misfire then occurs gives you more than a clue as to which part is faulty.
Of course, if the misfire stays on cylinder 4 you could be looking at an injector or something else but you will not have replaced a good plug and coil for no reason.

As for your lambda sensors you do not say which ones these are. I would expect you to have 4 on your car, 2 pre cat and 2 post cat.

The oscilloscope trace you show looks like one of each to me. Have a look at the other bank and see what they look like.
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