Front and Rear Pre-Cat fault [Citroen C5 V6 ES9J4S]

[aszaultz]

Dear all
1. About Front and Rear cat I was changed in oem product.
2. Today I test and saw downstream sensor information below
When i start engine idle mode Downstream Inactive --> value hode 0.5v
wait a minutes downstream active mode idle engine --> value around 0.7-0.8 V (Close Loop)
When I press a padle engine around 3000-3500 smooth engine (Close Loop) --> value around 0.3-0.4V
When I un press a padle engine go to idle (Close Loop) --> value around 0.7-0.8V
3. In this senario is possible main catalytic don't have ceramic or cytalyst and generated turbulence in main catalytic effect to exhaust non-uniform blow out and plug in main catalytic??

[Mandrake]

Were you not able to capture a set of graphs like the one Ben shows with the engine hot and running at a steady rpm ?

[aszaultz]

My oxygensensor voltage graph In first pic. In thirty sec. to fifty sec. Engine speed 3000RPM after that go to idle speed.

In second pic is road drive to my home.

Come with two fault.

[aszaultz]

Today, I inspect on exhaust when start engine first In idle speed smoke smell like a petrol gasoline come out. When push a pedal smell is
disappear. It normal operate(open loop) in first start too much richness or not? or My engine mixer is richness ??

[Mandrake]

It's normal for the engine to run rich when the car is started from cold, just like an old carburettor car where you had to pull out the choke on a cold engine...modern ECU management is so good that you hardly notice the engine is cold as far as performance and drivability goes, but behind the scenes it is richening the mixture when cold.

As well as that the oxygen sensors only work above 300 degrees celsius so even if the engine coolant is up to temperature if the car has been turned off long enough for the cats to cool down the oxygen sensors will not work until they heat up, which can be around 30 seconds to a minute after starting. During that time the engine will run in open loop and will err on the side of running rich, as soon as the oxygen sensors heat up it will go into closed loop mode, and if the engine coolant is up to temperature the mixture will then be corrected to an ideal mixture.

Your upstream oxygen sensor graphs look fine to me, but there is definitely a problem with the downstream sensor readings, particularly the rear bank. There are far too many transitions across the centre (0.45 volts) line, if the ECU records a large number of transitions relative to the upstream sensors it will report a fault.

If you look at Ben's graphs you will see his upstream readings look similar to yours but the downstream readings do not have rapid closely spaced transitions... the downstream reading should gradually drift high under heavy acceleration and gradually drift low under throttle off overrun, and be a smooth line near the middle at a constant idle but it should not rapidly go up/down/up/down as shown on your graphs.

Of particular concern is the period from 40-55 seconds on the first graph for downstream sensor for the rear bank which shows 20 transitions in a 15 second period - this should not happen if the pre-cat is working properly, and this will almost certainly flag a fault if it keeps occurring. It looks almost like electrical noise - is there any possibility there is a grounding fault in the wiring to the oxygen sensors ?

I'm no expert, but everything I've read up on about cats and oxygen sensors suggests that your pre-cats are just not working properly.

[aszaultz]

Hello. update my citroen c5 v6 pre-cat fault
Today on my free time I make ground wire(25sqmm vct cable) in point all ecu, butter fly motor, Engine Frame, compressor, alternator, gear and sub frame.
here this graph for up & down stream.

See the graph when idle is good but when engine was accelation graph in downstream is not linear.
and this picture in 3000 RPM zoom

In the evening I will clear all fault and test run to investigate Fault.

[Ben82]

I could be wrong but that looks like it's going open loop when accelerating? But that does look a lot better

What gave you the idea to replace the ground wire?

[aszaultz]

Hello, Now I was changed Main catalytic and both pre-cat (From dealer OEM part) my problem can't solve. See the graph.

When engine is idle downstream both of front and rear is smooth around 0.7-0.8V but when increase engine two graphs swing 0.1-0.8 like upstream sensor.

possible my downstream sensor malfunction??

Now I don't know to focus part to check in my problems. Who can inform for check in my problems?

Thank you.

[aszaultz]

Update..

Hello


Now I'm install Oxygen sensor extended as picture below. I used 90 degree type because I try to use left extended but don't work.


This two graph when I installed Oxygen extended 90 degree in front pre-cat. The graph show work fine and P0420 don't come for fault log. I was test run in 800km traffic drive and long run speed constant around 130-140 km/h

I don't install for rear pre-cat because for compensate front and rear.




I will test run for 5000km if the code P0420 don't come. I think it work for me.

#I buy it from e-bay.co.uk
Thankyou

[Mandrake]

Hi,

I really don't understand the purpose of mounting the oxygen sensor on a long tube ? It's also not clear to me whether you have only mounted the upstream oxygen sensor for the front bank on a right angle joint or whether you also mounted the downstream sensor in a right angle joint ?

While you may not yet have received a fault code I don't see how this will help your problem, also I'm puzzled why you modified the front bank when the rear bank is the one showing too much downstream activity on your graphs - even in your most recent graph there is still far too much activity in the rear bank down stream sensor and I believe its only a matter of time before this will set a fault code.

I was going to post a new scannerdanner video that was released yesterday in this thread but I couldn't remember what this thread was called to find it. I strongly recommend that you view and study this video in detail because it is an excellent, perhaps definitive video on how to diagnose catalytic converter efficiency / ageing problems:



I don't want to sound critical but it seems like you are clutching at straws trying to fix this issue without really understanding what is going on. I know you say that you have replaced the pre-cats with new OEM types but if they were working properly you would not be seeing rapid switching of the downstream sensors, its as simple as that. Are you certain they are manufacturer provided cats and not just after market "OEM compatible" types ?

Pay close attention to comments by Paul (Danner) near the end of the video where he says he has seen a LOT of problems with after market "OEM compatible" cats where they will keep setting fault codes as little as a few months after being replaced, because they are simply not good quality and not up to the job, and on many models only the original factory supplied cats will work properly.

We also have forum members who have had problems with 3rd party replacement cats for the Xantia V6 which simply do not work well enough to pass the emissions tests because they are not built to the same standard as the originals.

I really do think that your replacement cats are not genuine factory types even if they were sold as such, and that they are simply not good enough quality, hence the downstream oxygen sensor readings. It's possible that the rear pre-cat may even have been faulty on arrival given the large difference between the readings of the front and rear downstream oxygen sensors. Compare even your latest downstream oxygen sensor readings with those posted by Ben82 on the previous page, which is an example of correctly working pre-cats.

The fact that you have such a difference between the front and rear bank downstream oxygen sensor readings while Ben does not should make it clear that something is wrong with the rear bank pre-cat at the very least.

As I say, please study the diagnostic procedure demonstrated in the above video carefully especially the comments on the oxygen storage test and draw your own conclusions.

[Ben82]

I was thinking about this thread the other day and wondered whether there was an update.

Isn't this cheating? Looking at those extenders they seem to be off racing/off road use only, and seem like all they do is move the sensor away from being directly in line "of fire" of cat so the ECU thinks the cat is performing better than it actually is.

So it seems like this isn't solving the issue just masking it.

@Simon: I believe he's attached the extender to the front downstream sensor, since it's not pretty much a perfect reading, compared to previously.

[bamba]

It is possible that some oxygen sensor related faults can be caused by other parts/sensors reading incorrect, for instance a MAF may be giving out an incorrect reading for the volume of air passing, the reading is still valid and within the ecu's set parameters,therefore the ecu does not see the MAF as faulty but the engines fueling has gone to pot,and ends up running rich,giving oxygen sensor faults and cat failures, any thing that effects the fuel combustion will also give misleading faults, such as low compression/burning oil,valve timing,spark plugs,etc the car neads to go on a gas analyser to see what actually coming out of the exhaust. oxygen sensors are just at the end of a massive chain of events in your engine if some thing goes wrong at some point along the way, then what comes out the back will be wrong.

[Ben82]

Bamba: there's a bit of an issue with hooking the ES9J4S up to a gas analyser. The o2s come inbetween the precats and the main cat, so anything setting off the o2s may get cleaned up by the main cat so the gas analyser may end up saying everything is hunky dorey when it isn't.

I would also imagine if the MAP was faulty it would at least also hurt performance rather than just affecting the O2 readings.

The test that Simon links to is probably going to reveal more about the precats in this case than a gas analyser.

[bamba]

A gas analyser will still pick readings, even more so if something is a miss as in this case and will give a lambda reading regardless of the number of cats,what is this test by "simon" as i cant see a simon on here, im guessing you mean the one from mandrake, yes agreed a good worth will test, but the op here is doing it checking the symptom and may be not the root problem.
Imagine a bike tyre, that has gone flat, ive replaced the inner tube, but it still looses pressure, i replace it a second time, but still it looses pressure, i recorded the pressure drop over time on a graph,pump it up again etc, the root cause, a thorn still in the tyre causing repeated punctures.
The o2 sensors are just reading there values of what ever mixture right or wrong in in there.it is possible how ever that the op has fixed the problem after replacing the cats,but some damage to the cat or cats occurred in the mean time , so therefore still not functioning dis spite the problem being fixed.
Prob also worth checking continuity/short circuit. to ground or any other wire of the o2 sensors wiring from the sensors back to the ecu.
Its a bit hard work mind given the ops location and england skills, dosnt make easy reading

[aszaultz]

Now I'm fixed this problems by change both post cat and change all of ignition coil. I'm very happy in my citroen