Problems are coming faster than I can fix them...

Code as above, checked lambdas, both seem ok.

No obvious misfiring, haven't hit any big puddles.

So is there a good way to diagnose the next step? If not, is it new cat time?

Dreading those manifold bolts. Time to invest in a blowtorch.

check with mes if both lambdas are giving same reading then could be cat

As Dave said, if downstream lambda sensor (the one after the cat) is switching (0-1v) the cat is knackered however be aware the cat will dump oxygen every so often so don't confuse this reading with continuous switching.

Is engine light on and does code clear?

Engine light comes on and codes clear ok, but come back after maybe an hour of driving.

Upstream cat switches 0-1v approx, downstream cat switches at same frequency, but smaller amplitude, maybe 0-0.6v from memory. Tis would suggest that the cat is fine as oxygen is being consumed?

The issue is, I don't know what "low efficiency" translates into in terms of measurable parameters, that prompted my other post on workshop manual, which must contain sufficient diagnostic information for fiat techs?

The pre cat should bounce between 0 and 1v as said As it strives to get the perfect a Stoitchiometic mixture (ie 14.7 bits of air to 1part fuel)

This never happens really - dont ask me why but there we go

the post cat looks at the performance of the catalyst and adjust the fueling in the long term

So if the post cat is bouncing quiet alot like the pre cat sensor, it would say cat to me

but i'd be tempted to swap both of them around
Pre to post
post to pre and see if the results look the same
If they do - it means the lamba are right and you best dig deep....

You 100% sure there are no leaks or cracks? ie sealed exhaust system
Tempguage working correctly? so its swapping from open to closed?


Ziggy

Checked for leaks, seems like there is no problem.

Temp gauge.....what temp gauge? I've got the budget model......electric front windows were an added extra , you can forget about something useful like a temp gauge (although I can look at this with my reader)

I suppose I could also check the calculated fuel trim.....but the issue is that I have no baseline to compare it with.

You can defintely feel it running a bit rougher

atom0007 said:

Checked for leaks, seems like there is no problem.

Temp gauge.....what temp gauge? I've got the budget model......electric front windows were an added extra , you can forget about something useful like a temp gauge (although I can look at this with my reader)

I suppose I could also check the calculated fuel trim.....but the issue is that I have no baseline to compare it with.

You can defintely feel it running a bit rougher

Click to expand...

the thing is - if the sensor aren't responding how they should

The car looks to revert to a base line programming, so it knows the fault can be ignored and keep you running, but leaves the light on till it checks and see's if the problem has been fixed or not

Ziggy

exactly - but this doesn't help in looking at the sensor output, i still need a baseline on that....

You might see if the Seicento Technical Manual has anything of use. After all, it's the same (on early run MPI cars) the same aweful ECU and cat/lambda system. In the downloads section.

i know for a fact i'm going to have this code when i read the ECU, the only difference is................ i've just slid straight on in a tight right, the handbrake helped send the rear around the corner, BUT i hit a ditch and it's now ripped the cat OFF the manifold, so looks like a nice warranty claim will be put in

If downstream lambda constantly switching the you need a cat.

T14086 said:

If downstream lambda constantly switching the you need a cat.

Click to expand...

I don't believe that.....the downstream must switch...I have traces from a while ago when it was working ok, showing downstream switching.

nikkiy9 said:

i know for a fact i'm going to have this code when i read the ECU, the only difference is................ i've just slid straight on in a tight right, the handbrake helped send the rear around the corner, BUT i hit a ditch and it's now ripped the cat OFF the manifold, so looks like a nice warranty claim will be put in

Click to expand...

On the upside, it's easier to diagnose....

Haha, yeah, that's true, I will upload a picture of the damage once I get the cat off, manifold is already removed

atom0007 said:

I don't believe that.....the downstream must switch...I have traces from a while ago when it was working ok, showing downstream switching.

Click to expand...

Then your cat has been inefficient for a while.

T14086 said:

Then your cat has been inefficient for a while.

Click to expand...

Interesting.

Surely the downstream reading must switch, albeit with a lower amplitude than the upstream one?

If it was constant, that implies that there is the same amount of oxygen in the exhaust gas, regardless of how the ecu was setting the mixture.

That doesn't make any sense to me....

the Pre cat sensor is a very up and down very quickly as it adjusts the instant fuel mixture

The post cat sensor is still working the same, however its seeing a hella lot less of peak and troughing, it will fluctuate but no way near as bad

Ziggy

atom0007 said:

Interesting.

Surely the downstream reading must switch, albeit with a lower amplitude than the upstream one?

If it was constant, that implies that there is the same amount of oxygen in the exhaust gas, regardless of how the ecu was setting the mixture.

That doesn't make any sense to me....

Click to expand...

See post #3

Lambda 2 (downstream) if monitored (depending on manufacturer, strategy condition etc) will normally sit around 0.4-0.6v. Remember the lambda 2 is monitoring the efficiency of the catalyst nothing else.

Can't say I fully understand the science of it....but I don't ignore good advice so it's time for a new one.

What's a reasonable price? Fit myself probably.

I'm happier now, I have done a bit of reading about this, so here goes for those interested.

My confusion was that when the ECU changed the mixture strength, I expected the variation in oxygen to be measurable before and after the catalytic converter. What I didn't know is that catalytic converters can store oxygen, and act like a damper.

When running with a lean mixture, there is an excess of oxygen in the exhaust gas. However, this excess (largely) does not make it past the catalyst, which can store it in the Cerium Oxide.

When running with a rich mixtue, there is a deficit of oxygen. The stored oxygen is released by the Cerium Oxide in the catalyst and (largely) oxidises the excess hydrocarbons (fuel).

In other words, the catalytic converter/ECU works to maintain a constant oxygen concentration post cat, and has to balance off the competing needs of extra oxygen for oxidising unburnt fuel, against the needs of lower oxygen for reducing NOx.

In short, like the helpful folks on here said, if it's switching too much, it's broken. (But don't ask me what "too much" means ).