What the **** are diagnostics for?

Putting a wire from the cat to a body earth would remove any PD in the ground levels of the sensors to the main ecu ground. Potentially if the cat is isolated then a generated earth loop current could offset the sensor value and hence create an anonymous fault indication when the sensor is actually producing the correct result.

This would eliminate the potential errors that could arise when the ratios are compared eg. Precat and postcat sensors where one may have a good electrical path to earth and the other not so good. The sensors rely on temperature and consumed energy based on the width of the pulse required to maintain the operating temperature if there is a bad earth or an earth loop current then the reported value to the ecu would be incorrect despite the function being correct. Result being no misfire or smell but reported error in the O2 ratio across the cat.

Just a theory may not be the case but I have seen this occur on other high performance engine systems.
 
Nelly Welly said:
Putting a wire from the cat to a body earth would remove any PD in the ground levels of the sensors to the main ecu ground. Potentially if the cat is isolated then a generated earth loop current could offset the sensor value and hence create an anonymous fault indication when the sensor is actually producing the correct result.

This would eliminate the potential errors that could arise when the ratios are compared eg. Precat and postcat sensors where one may have a good electrical path to earth and the other not so good. The sensors rely on temperature and consumed energy based on the width of the pulse required to maintain the operating temperature if there is a bad earth or an earth loop current then the reported value to the ecu would be incorrect despite the function being correct. Result being no misfire or smell but reported error in the O2 ratio across the cat.

Just a theory may not be the case but I have seen this occur on other high performance engine systems.
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I rang my indy after reading your post, he said its very unlikely as the diagnostic equipment they use would show a sensor fault, thanks for your continuing help/thoughts tho.
 
It would not nec show a sensor fault it would just show up as an incorrect ratio across the cat.

Let me know where you end up but gut feel is the O2 sensors out of range of each other.

Just had a thought have you had the Indy check the engine coolant sensor to make sure it is showing as the engine is hot or the cold running will kick in and cause an imbalance in the O2 sensors.
 
Nelly Welly said:
It would not nec show a sensor fault it would just show up as an incorrect ratio across the cat.

Let me know where you end up but gut feel is the O2 sensors out of range of each other.

Just had a thought have you had the Indy check the engine coolant sensor to make sure it is showing as the engine is hot or the cold running will kick in and cause an imbalance in the O2 sensors.
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Thanks I will mention it to them tomorrow, they will probably be fed up with me by now :roll:
 
I think NellyW is barking up the right sort of tree mate. If as you say your light comes on under hard use it's running too hot and too lean producing too much NOx. This suggests A) that the fuel/air mix is going off which could be down to anything in fuelling system that affects inlet fuel air ratio, including a split inlet, faulty injection or a sensor triggering improper fuel mix (e.g temperature as NW suggests). Or B) you DID HAVE a fuelling fault which was fixed but it stressed and damaged the cat causing it to run out of spec under certain conditions. This doesn't mean it won't pass an emissions test and won't be helped by Redex in your case as that is to fix a dirty contaminated cat caused by over-fuelling, or rich running often down to town use on a cold engine.

Whilst you absolutely should eliminate other causes it is an inefficient cat fault code and the story is probably in the headline. You did have a fuelling fault (manifold) and in all likelihood you have a cat that is simply under-performing under certain conditions. I think you will either end up having to live with option D (clear and drive it which is what I'd do) or change the cat.

It's why in my heart I love classics with carb's and a choke flap :oldman:

Worth a read http://robisonservice.blogspot.co.uk/2012/05/those-dreaded-p0420p0430-catalyst.html
 
Ewazix said:
I think NellyW is barking up the right sort of tree mate. If as you say your light comes on under hard use it's running too hot and too lean producing too much NOx. This suggests A) that the fuel/air mix is going off which could be down to anything in fuelling system that affects inlet fuel air ratio, including a split inlet, faulty injection or a sensor triggering improper fuel mix (e.g temperature as NW suggests). Or B) you DID HAVE a fuelling fault which was fixed but it stressed and damaged the cat causing it to run out of spec under certain conditions. This doesn't mean it won't pass an emissions test and won't be helped by Redex in your case as that is to fix a dirty contaminated cat caused by over-fuelling, or rich running often down to town use on a cold engine.

Whilst you absolutely should eliminate other causes it is an inefficient cat fault code and the story is probably in the headline. You did have a fuelling fault (manifold) and in all likelihood you have a cat that is simply under-performing under certain conditions. I think you will either end up having to live with option D (clear and drive it which is what I'd do) or change the cat.

It's why in my heart I love classics with carb's and a choke flap :oldman:

Worth a read http://robisonservice.blogspot.co.uk/2012/05/those-dreaded-p0420p0430-catalyst.html
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Thanks for the input, looks basically like I will have to live with it until its coming on every day.
 
Just for arguments sake if it were something as simple as a duff spark plug or air leak(as has been stated on tinternet so must be true :roll: )-wouldn't my zed run crappy round town etc...
 
Air leak or bad spark would give irritable running. I really feel it's more likely to be a sensor error as it's running fine.
 
Nelly Welly said:
Air leak or bad spark would give irritable running. I really feel it's more likely to be a sensor error as it's running fine.
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Ah okay I have a STFT B1 at 4.68%
LTFT B1 at 1.56% freeze frame data from code reader -does this show anything amiss does anyone know?
 
The first stft value is well in the normal range the ltft value is possibly a little high and should return to zero, if this remains positive and above 1% the this would indicate the system is having to add fuel into the mixture in long term driving evident of an unmetered air leak. It's likely to be after the mass air flow but before the manifold.

This would support the error in the O2 sensor theory.

If you listen can you hear a very slight hiss when the engine is running ?
 
Nelly Welly said:
The first stft value is well in the normal range the ltft value is possibly a little high and should return to zero, if this remains positive and above 1% the this would indicate the system is having to add fuel into the mixture in long term driving evident of an unmetered air leak. It's likely to be after the mass air flow but before the manifold.

This would support the error in the O2 sensor theory.

If you listen can you hear a very slight hiss when the engine is running ?
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I will have a listen tomorrow, is that for a leak?-is it possible the indy's smoke test has missed something?
 
There will be a leak inwards not out. It's the vacuum of the intake sucking in air that is not being metered through the maf.. This results in the fueling trying to correct the O2 sensor ratios by increasing the fueling.

That's why it gives the error as a weakened cat result.

It's not a blowing leak but a sucking leak the fueling changes will keep the engine running sweetly until the leak gets to big then it will start to run rough at tickover but smooth on raised rpm.
 
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