The lack of posts like yours, and the lack of interest/contribution to them, is the main reasons why i gave up posting stuff like this too. Not many people seem to want a debate for fear of looking a fool ? What a shame that we make each other feel like this

I did start a reply on the same day you posted, but couldn't finish it cos i had to go out. It takes time to think about, and type a worthy reply to some posts, and yours was one such post. I think you removed it too soon, but i understand why.

Dave F

After 2 Days ??????

Good job i don't treat all the other posts like this, as Dave points out, someone may be out, busy, on holiday, dont have an answer......

Peter

I probably spat my dummy out too soon .

I Will stick it back up when I get a mo!

Sorry for that

Dave

Often with posts such as yours many members will have more time to think and reply at weekends

Bit of an site update coming tomorrow along with a new forum........

Peter

As George said "my tuppence worth is that it could just be the knackered cat making it keep dropping out"
I think if we had a flow chart of the programming on an ecu we would know or be able to work out why it drops out. You know how a simple program for a kettle would ask - has the kettle got water in? yes = turn it on, no = do not turn it on and store a pending code. Then it would go back to the beginning and ask the first question again etc until it had three pending codes then flag a fault, could this be happening with the ecu? The trouble with a lot of these things now is they all have little quirks that we don't know about until somebody like yourself puts the time and effort into investigating why, because the manufacturers will not release info to help us.

I don't post that often because by the time I've thought about it, checked on what I am saying and got enough confidence to post without looking a fool - somebody else has already done it. It is reading posts like yours that is slowly building up my confidence in what I am thinking and diagnosing. All the best.

Graham

Regards
Steve

But then, when do you learn anything???

Sometimes, you need to take the fall, stand up dust yourself off, then carry on walking, feeling a little wiser.

In truth I dont reply to many posts either unless I feel I have something useful to offer which is rare.

I am finding that since I got the Pico, I have been able to get a much greater appreciation of what’s going on with many of these vehicles systems. My thinking is that if I am intrigued by what I am discovering, then other like-minded techs will find it of interest too.

Anyway, now I have re inserted my dummy I will gladly keep sticking my findings on here & maybe we will all learn some more.

George. The pictures are uploaded to the server that hosts my website. All I do is put the address in the bit at the bottom of the posting.

New Cat (genuine) is being fitted next week, so hopefully I will get time to confirm the repair & report back

Thanks once again

Dave

All a bit of a guess.

Regards
Steve

Good post.

you need to have channel A on B1S1 and channel B on Injector Pulse.

You have confirmed the HEGO sensors are working fine so, when the volts drop down to zero they are indicating the engine must be running very lean. when the car returned and you confirmed the DTC P0420 was this the only DTC Stored.

Because it as gone into open loop there will be not correction.

check injector PW when in closed open and see what happens to it when in Open loop.

when at idle and in closed loop what is the C0% reading then. I would expect around 0.50or a little lower.
Also have you a simulator if yes set it to DC volts and put 0.7 volts on the signal wire on B1S2. But get the engine upto temp first.

this May fool the ECU into thinking the CAT is OK , and good enough for static testing . i.e no vehicle speed or drive cycles completed.

keep the info coming and the answer will come

In a rush again but here goes...

In my experience a failed CAT ( unless it is restricting the exhaust gases ) will not cause a higher CO than 0.7% so you appear to have a fueling issue here. Maybe the CAT just can't cope, hence the rear sensor switching ?

I would like to see the lambda readings as well as the CO% when the sensors are switching and flat lining. The lambda reading tells you if the system can achieve correct AFR, so its important to look at this and the O2 sensor patterns at the same time. The sensor behaviour and/or the fuel trim figures will show you how hard the system is working to achieve lambda 1.000.

I would also be doing a manifold vacuum test and an exhaust backpressure test.

Dave F

I must admit that I perhaps got a little exited with the scoping aspect & have not concentrated enough on my gas readings. I did consider scoping the injector pulse width to see how it reacts to the various conditions that I was seeing.

I did wonder for a while if the flat line periods were as a result of the PCM setting a constant fuel strategy based on the prolonged steady 2,500 rpm. I thought it may have looked at the conditions & decided on a set pulse width, whilst the same conditions continued. That was until I noticed on the scanner that it had dropped out of closed loop.

The car is back with the customer for the time being. I will try to put some proper time in on it before & after I replace the catalyst.

Thanks for the debate

Dave Hill

I have it booked in for three days next week (he's on holiday).

Cheers

Dave

Regards
John

It was a coil failure. He reckons he only drove it four miles. Mind you, when I approached the car with scan tool in hand, he was revving the nuts off it & it was missing like a pig (whatever that means).

Actually it came in today for a few days & I spent some time scoping both sensors & getting some gas readings. Guess what, the bloody thing wont flat line now & switches fine. I had it on test for over an hour at 2,500 rpm & never did it go open loop. The gas readings were as expected for a dead catalyst.

I have it for a few days so I will try a few times to get to the bottom of this.

Cheers

Dave

John

Unfortunately the car just would not misbehave (fortunate for the customer). So we just fitted the new catalyst. One thing that did become apparent was that the monolith was loose & disintegrating. I dont think it was severe enough to be causing a blockage, but it wasn’t something I expected to see after a simple misfire fault. Probably a coincidence I suppose.

I did take some pre & post O2 sensor captures at various rev ranges with the new catalyst. If anyone is interested I shall post them.

Cheers all

Dave

Since taking these captures I have found that the Laptop charger was causing interference & also the lead that I was using for channel A appeared to be causing allot more noise than the others (now demoted to channel C )

If anyone has any views or corrections to my comments then don’t hold back (manners appreciated of course )

Cheers all

Dave (Hill)

The emissions were absolutely spot on!

Yes I am sure you are right about the downstream O2 sensor flat lining. However, I suppose there must be a limit to what the catalyst is capable of dealing with (volume wise).

This is the first capture of this nature that I have taken so I can’t offer a confident generalisation. It would be interesting to perform the same test on a 60,000 mile catalyst that is still functioning efficiently (comparatively I mean) to compare the level of switch & at what engine speed.

I think that what we are seeing in the first frames of the animation is the result of the catalyst working at the limit of its Oxygen storage capacity. It looks like the catalyst is saturated with oxygen at this engine speed & the excess O2 is what is driving the lean state on the downstream sensor. In the middle section of the animation, when the RPM is reduced to 2,500 RPM & the downstream sensor volts rise, it shows that there is no Oxygen present. This switch from low volts to high volts is not a switch in the same sense as we see it in closed loop fueling; it is more a display of how the catalyst is coping with the volume of gasses thrown at it.

Please don’t take my comments as Gospel, as I am only saying what I believe is happening in the captures. My opinion is always open to question!

There is a very interesting post from William Mclarren on the subject of Catalyst efficiency.

Tom

Thanks for the comments mate. I don’t have allot to offer diagnostically, but I enjoy discovering things with the Pico & I hope others are learning as much as I am from the images.

Cheers all

Dave (Hill)

Am I missing something, or isn't this cat knackered?

Keith

Regards