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(Post Link) post #1 of 30 Old 01-09-11 Thread Starter
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Would you trust a 2nd hand O2 Sensor?

Money is getting tighter than scotsman at the moment and im looking into minor niggles on the car at the moment without spending huge money.

There is a tiny hesitation between 1500-2000rpm in a high gear, a little stutter. Somebody suggested it could be the Lambda sensor. Its not very noticeable, but I wouldnt mind tracking down the cause and fixing it, without spending €120 on a new sensor when it might not cure it.

So there are 2nd hand, genuine ones on ebay for about €40 delivered. What do you guys reckon? Would you trust one?

The car also idles a bit funny when hot, between 900 and 1200rpm sometimes. Ive cleaned the throttle body, done a Throttle reset, changed the MAF (Genuine Bosch) and checked for leaks in the intake pipe (unless they are tiny, I dont see them). Idle actuator somebody said, but 2nd hand ones wont work well apparently

Neither of these issues are serious, but I just dont want to throw a whole heap of money at them either for it not to be those bits.
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First port of call would be removing the coil pack and checking for water in the plug wells as dermo had some fun with the v6 when he got it
 
(Post Link) post #3 of 30 Old 01-09-11 Thread Starter
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Changed the plugs not too long ago, there was a bit of oil down in the number 1 cylinder, but i cleaned it all out and the problem was still there, unless its damaged from oil contamination?
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My experience of a failing/failed lambda is that when you try and crawl along at low revs in 1st gear in traffic the car is constantly speeding up and slowing down as the ECU adjusts the fuel mixture.

Like you say a vac leak could also cause your issue - they can be very hard to find and sometimes only happen while the car is accelerating, either due to the movement of the intake pipes or the increased vacuum.
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What make plugs were they as even petrol can cause these "weak" idle problems
 
(Post Link) post #6 of 30 Old 01-09-11 Thread Starter
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Genuine Alfa plugs went in her.

What you mean that petrol can cause weak idle problems?

Will try the 1st gear crawl. Thanks.
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Can you check the outputs of your lambda sensor on a diagnostic machine to see if they are switching properly?
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(Post Link) post #8 of 30 Old 01-09-11 Thread Starter
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Wouldnt know how to do that

Stutter only happens when its fully up to temp. Wont do it when its cold.

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Tough call then, you could ask a garage to check, but this will cost you and may just confirm what you already suspect, or you may find the issue is something else entirely.. Replacing parts on a gut feel, without testing whether or not they are working as they should is OK with a lot of experience, 90% of the time you will get it right. But unless you really know what you are doing it might be better if you get the issue confirmed, replacing parts without proper diagnosis can be a bit of a lottery. Also you will have no way of checking if the used lambda sensor is switching as it should once you fit it.

If you are into working on your own car you might want to consider buying yourself a cable and downloading a copy of Fiat ECU Scan so you can pinpoint the problems before starting to change parts.

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(Post Link) post #10 of 30 Old 02-09-11 Thread Starter
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Ordered a Cable and going to download a demo copy of Alfadiag or FiatECUScan (to make sure it connects) and then see if it will read the Lambda.

What exactly am I looking for with the Lambda readings? What is Switching?

Last edited by jf_cole; 02-09-11 at 11:28.
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Hey JF...

If you're around Cork I can help you take a look if ya want??

Here are two links that might be of interest to you:

Just Lambda NTK, Suppliers of NTK lambda sensors by post..

Oxygen Sensor Information

In short the voltage on the signal side of the O2 sensor will 'switch' ie the voltage will swing from around 0.25volts to 0.85volts and back at around once a second-ish. If it's not, or sluggish then you have an issue.. of course it might be giving a false reading altogether.. I guess you don't want to go poking holes in the insulation around the O2 lead or shoving probes into connectors etc so the route you've chosen is wise.. i.e. the ELM cable and the FIAT scan software.

TBh honest if the O2 was duff I'd expect a diagnostic light on the dash... but the ELM/FIATdiag will list any emission codes/errors stored in memory... if there are any in there it may provide a hint to the root cause.

What engine do you have in your car ? 2.0TS? if so they have two O2's (from memory).. from the diag software the sensors (when up to temperature) should be switching slightly out-of-phase.. that is, their voltages should almost be the opposite of each other at any given time.. but they should be swigging with the same frequency.. i.e both swigging one time per second... (if that makes scene?)......

This is a guess, but I'd say your O2's are fine.... if I was to gamble I'd say it's the throttlebody. If it's the 2.0TS you have I'd be recalibrate the butterfly flap on the throttlebody. I've had to do this in the past with our car in the past due to driveabilty and erratic rev issues. This problem DIDN'T bring on the diag light either. The revs were a bit erratic, after the cal.. all fine...

I don't know if the FIAT ECU scan software had the procedure/algorithm to do this, I'd assume ti does.. I had to use Snap on gear to do it at the time, but it only takes a min or twp and the difference in the car (I found) was vast....

I hope it's a simple fix in the end......

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As cathal said you are looking at the voltage but also depending on the speed of alfadiag you are looking at the frequency of switching. If alfadiag has the "lambda integrator" function as i use the examiner and not alfadiag you are looking to see if the ecu stays within the box.... but this integrator is not the lambda probe but is the rate of correction in the ecu
 
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Hey jf... any luck with your car?
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(Post Link) post #14 of 30 Old 07-09-11 Thread Starter
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Hey, Thanks for replies guys.

I tried a new (2nd hand) coil in number 1 plug as that had oil in it. No joy. I couldnt try the number 2 plug as the coil had a short leaded number 2 plug coil.

Waiting on the cable for alfadiag/fiatscan to arrive and will give that a go then. Hoping one of these in its free form will show the lambda.
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theres one for sale on Adverts.ie

Alfa 156 20ts Lambda Sensor For Sale in Midleton, Cork. Buy Car Parts & Accessories

€55 for it i think. might even able able to get it for less if you bargain him.
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(Post Link) post #16 of 30 Old 07-09-11 Thread Starter
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theres one for sale on Adverts.ie

Alfa 156 20ts Lambda Sensor For Sale in Midleton, Cork. Buy Car Parts & Accessories

Ä55 for it i think. might even able able to get it for less if you bargain him.
Thanks, if you look in the comments, I asked him back in July whether it was a bosch (now realise it should be NTK?), but it seems to be spurious.

Spurious MAF's & O2's never seem to last.
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didnt look at the comments. LOL

just go for a spurios out for now. they arnt that bad.
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(Post Link) post #18 of 30 Old 09-09-11 Thread Starter
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FiatEcuScan now setup on the laptop and reading the Lambda volts and correction etc.

Didnt get time to get it warm or go for a spin though.

There was a code stored that the Lambda parameters were high, but it wasnt showing on the dash, just a stored code. It said it could be due to a leak in the exhaust pre lambda or intake post MAF. Im getting the downpipe->cat gasket replaced as there is a small leak in the morning, this may be it.

Have to try read the lambda signals after that to see.
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That sound cool the fact you found a leak....

A code stored but not bringing on the diag light points to an infrequent event..would.be interesting to.see the O2's signals when.warm and after the leak is plugged..
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(Post Link) post #20 of 30 Old 10-09-11 Thread Starter
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Lambda switching 90% of the time fine, 10% a biy slow.

I take it that on full throttle the signal stays high and when off throttle coasting in gear it stays low?

The lambda status at idle was all over the place, from bottom limit to rich to lean even saying cold when clearly it wasnt. On a steady throttle it did the same, constantly changing. Full throttle it stays rich and on coasting in gear it says lean or bottom limit.

Are these normal?

I did an idle actuater test and the idle fluctuations are worse now might do a throttle reset again and hope fpr the best.

Exhaust leak cured, but made no difference.
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On full throttle the ECU runs open loop, so lambda reading (whatever its showing) is ignored.
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Originally Posted by Pud237 View Post
On full throttle the ECU runs open loop, so lambda reading (whatever its showing) is ignored.
They go onto a WOT map don't they? Hence why I get such poor mileage outta my 156 lol I can get it to 9mpg
 
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On full throttle the ECU runs open loop, so lambda reading (whatever its showing) is ignored.
True but the map is close to lambda at high revs when in open loop unless the engine is trying to accelerate as otherwise you would have cats burning up big time
 
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They go onto a WOT map don't they? Hence why I get such poor mileage outta my 156 lol I can get it to 9mpg
Yea... but u drive like a maniac
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(Post Link) post #25 of 30 Old 10-09-11 Thread Starter
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So, it looks like then the O2 Sensor is running normal?

Im not sure what the 'lambda status' should look like on FES, should it switch like a maniac, including saying cold, bottom limit, rich etc?

Thanks
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