Desperately seeking help with diagnosing over fueling.

Nardo

Nardo

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Desperately seeking some advice here. I have a 197, with a over fueling issue, that I am really struggling to find a solution to, and is causing MOT fail, with lamdas reading 0.95-1.36-1.028.

The car has new cat, new bosch lamdas, new NGK plugs, new pcv. Has cambelt done last year, newish NGK coils, fresh oil, water and fuel pumps changed last year. It is running a milltek cat back, with a AS homologated CAT. MAP is a year old, two O-rings and tie wrapped in place. New thermostat last summer, always fresh oil.

When I brought this car, it had no cat. I fitted one, and the milltek for MOT and it just passed, last time. This time, I brought a new cat, the same as before and no changes to the readings.

I'm wondering, if the car has been mapped for no cat, group N exhaust prior to me, whether this would be causing these issues, and would be why we see no changes when swapping out these parts.

Live readings go 0.9 0.9 on WOT, jump around from 0.7 - 0.9 and down.

I collected it from a motorsport garage were I had the exhaust checked for leaks, vacuum leak checked, new plugs, and lamdas fitted. Could find nothing wrong, mechanically perfect, no misfires and runs really strong, no hickups, flatspots pulls very hard.

When I collected it, had the OB2 connected, ran through the emission cycle and all green. Next start, when I took it to the MOT, reports cat issue (which is brand new, under 500M)

I'm lost with what next steps to take, and having a real issue diagnosing this, any help or knowledge really appreciated.
 

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RSRowe said:
What exhaust manifold does the car have?
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Manifold is standard, asked the last garage to check the exhaust, they build customs and said it is OK (but i do not know the internals of the manifold cat, the 2nd is new)
 
RSRowe said:
I feel like the manifold cat would solve your issues for the least amount of money.
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Thanks, I think you might be right, but do you think that would account for the high lamdas? same readings, on the previous lamdas, i changed them both. Previous, and new both bosch, but no changes to the lamdas on the road, live readings more or less the same. Same with the cat swap (2nd).

The car had no 2nd cat when I got it couple of years ago or so. No matter what, the lamdas have always more or less, read the same, with, without 2nd cat, and all new parts mostly.
 
The first lambda is before the first cat isnt it? then i dont see how having cats or not is going to make a difference to the air fuel ratio.
 
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VeiRoNv2 said:
The first lambda is before the first cat isnt it? then i dont see how having cats or not is going to make a difference to the air fuel ratio.
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This is the part I am confused by, the fuel ratio's don't appear to change with any cat changes, or anything else for that matter.
 
Because you need to look somewhere else,I feel like going to somebody like Engine dynamics or EFI where they can see exactly what's going on in the parameters it's your best bet instead of blindly keep replacing parts.
 
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Not blindly changing parts, Renault reported the cat as gone, which I replaced. Rest is service items getting it were I want and lambdas to be sure. The car had belts done, fuel pump, thermostat, etc at Renault. So presume this is all correct, and pointing out everything is in good condition, serviced, etc,
 
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VeiRoNv2 said:
Because you need to look somewhere else,I feel like going to somebody like Engine dynamics or EFI where they can see exactly what's going on in the parameters it's your best bet instead of blindly keep replacing parts.
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Wish I could, I am English but over in Spain and this is not easy in another language
 
Air filter is a KN, clean. Same figures more or less with a Pipercross, checked the inlet and connections, sealed them.
 
If you're changing the exhaust then the map will surely be out, no? If it was mapped for de-cat, then adding a cat isn't going to change a great deal and I'd suggest looking at getting another map for when MOT is due and you have to add the cat in again... Then when MOT has passed emissions, you can change back to the previous map and de-cat setup.

Seems like a lot of faff for probably not a lot of gain in terms of power, especially on these N/A engines. You might find a suitable map with the cat(s) in place allow the car to run better and shouldn't be an issue come MOT time.

Or if you can find a friendly MOT tester, that could help.

Sometimes, MOT tested will suggest taking the car out for a "spirited" drive right before the do the emissions testing as getting them [very] hot can help with passing emissions tests... Saw you're in Spain so not sure how strict things are over there, though!
 
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Does this happen on all Cylinders or only one? I would get a code reader and see if its only on one cylinder, if yes then change your Injectors and see if the Problem will transfer the any other Cylinder.
 
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Could be fuel map, if it has been remapped. You said the car previously had a de-cat? Was that a full de-cat or just removing one?

With an OEM cat in place, a fuel map is typically on the lean(er) side, this is to generate the exhaust gas temperatures required to activate the catalytic converter and to ensure there is enough O2 in the exhaust gas for the oxidation reaction to occur inside the catalytic converter.

When you de-cat a car, you no longer require this additional O2, nor the higher EGT, so the tune typically introduces more fuel, taking advantage of the free-er flowing exhaust, which makes more power. If you then reintroduce a catalytic converter back into the system, without altering the tune back to how it was, you may be overfuelling and causing the emissions test failures you describe. This could also be causing early failure of the catalytic converter due to unburnt fuel getting into the cat.

A workaround for the MOT might be to take it for a spirited drive before the test. Use high revs for extended periods of time, which will lead to higher EGTs. This might be enough to burn off any deposits of fuel on the cat, allowing it to work as intended (at least for the MOT).
 
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I've done exactly this for MOT,car was mapped by EFI without any cats at all then fitted back the main cat and it still passed no problem, results are in my thread,so not sure if it could be just the map on yours or a faulty part
 
VeiRoNv2 said:
I've done exactly this for MOT,car was mapped by EFI without any cats at all then fitted back the main cat and it still passed no problem, results are in my thread,so not sure if it could be just the map on yours or a faulty part
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Just want to chime in with the same set up. EFI mapped my car with no cats and each year I whack the main cat back in and it passes MOT without an issue
 
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