CEL from high flow cats

jasst

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2,313
Just to revisit this, I put oem cats back on for the mot, and have left them on as an experiment. No cel yet, and I definitely would have by now with the sports cats, but having suffered cat failure once in my life, I am now bricking it that it may happen again.
 

Twinspark

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460
If you’ve got the early model without the primary cats in the headers I’d say you should upgrade for peace of mind if you can afford the relatively high cost.
 

3hcp

Member
Messages
238
Just to revisit this, I put oem cats back on for the mot, and have left them on as an experiment. No cel yet, and I definitely would have by now with the sports cats, but having suffered cat failure once in my life, I am now bricking it that it may happen again.
Hi James,
did you ever solve the cel problem as I am having the same problems with the larini cats.
if I’m dawdling it’s not hot enough Cel then on motorways I get slow down over temperature.
regards
H
 

Zep

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9,110
How old are your lambda sensors? As they get old the cycle time increases making them less likely to read correctly. I’d be checking the long term fuel trims as they tend to go rich with lambda issues.

If yours is the type with the thermocouples (early cars) this might be the source of the slow down message.
 

3hcp

Member
Messages
238
Yes its the early one with thermocouples, below are the error codes.
it says slow down in red on dash after as little as 20 minutes cruising on the motorway (not speed dependent and fine when on A roads at varying speeds) so presumably too hot, do the thermocouples fail or is the temperature out of range. I presume the lambdas should be ok as they were fine on the standard cats.
is there a way to test the thermocouples/lambdas? Or has anyone remapped the range out of the system?
i have also had the orange cel with code p0431 temperature below threshold when dawdling but not as often.
seems like my options are
1 put the original cats back on
2 get a remap (if that’s possible)
3 change thermocouples/lambda with no guarantee of success.
any suggestions greatly appreciated
 

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Zep

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9,110
Is P0431 the only code you are getting? That is for bank 2. I suggest that if it was an overall issue you’d also be getting P0421, which would be bank 1.

I assume you have checked for leaks etc?

You can check the cycle time of the lambdas, which gives an indication of condition, as I said above.

Reading the code description for the thermocouples, it reads as a sensor range/performance issue, not a high or low temp.

1694976695274.png

While there are few guarantees, it seems likely that you have at least one faulty lambda and you need to look at the sensors to see how they are fitted and wired.

The higher flow cats will change how the sensors read and operate, so it’s not a surprise that if they were heading toward the end of their life that they could then be tipped over the edge.
 

jasst

Member
Messages
2,313
Hi James,
did you ever solve the cel problem as I am having the same problems with the larini cats.
if I’m dawdling it’s not hot enough Cel then on motorways I get slow down over temperature.
regards
H
No, I'm still running stock system, and no cell. I did investigate having a custom system made a few weeks ago and talked to the fabricator about cel problems with sports cats, he suggested using lambda cheaters as a possible solution. I always thought they were just extension tubes for the lambda, but he said they actually have 'mini cats' in them to fool the system, may be worth a try for not much expense. From memory I used to get ' P4021, and P 4031' codes from memory.
 

allandwf

Member
Messages
10,958
Extensions for the lambda are a well known way of getting around faults thrown by them, but the thermocouples, if that is what they are and not a generic term, should test as short across them with a meter and should generate a mV signal. If they are resistance devices then each bank should read the same when cold typically somewhere over 100 ohms . Neither type usually drift they either work or they don't.
 
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3hcp

Member
Messages
238
Is P0431 the only code you are getting? That is for bank 2. I suggest that if it was an overall issue you’d also be getting P0421, which would be bank 1.

I assume you have checked for leaks etc?

You can check the cycle time of the lambdas, which gives an indication of condition, as I said above.

Reading the code description for the thermocouples, it reads as a sensor range/performance issue, not a high or low temp.

View attachment 119019

While there are few guarantees, it seems likely that you have at least one faulty lambda and you need to look at the sensors to see how they are fitted and wired.

The higher flow cats will change how the sensors read and operate, so it’s not a surprise that if they were heading toward the end of their life that they could then be tipped over the edge.
Just looked at the recorded data as suggested, on the O2 sensor voltage one looks distinctly different to the other. Would that indicate a failing lambda bank 1?
 

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Zep

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Your code says bank 2, so it might be the other way around. If I was trying to diagnose it, i’d swap the sensors and see if the behaviour followed the swap. In theory you should see the fault move to the opposite bank, ruling out another cause.
 

3hcp

Member
Messages
238
Final thought, on the standard version there are 2 cats and 2 lambdas one before the first cat (182837)and one after (191412)which are different part numbers. What’s the difference?
on the larinis there is only one cat at the rear with one lambda at the front end, which lambda should be used front or rear and could this be causing the problem. I think I’ll invest in two new lambdas anyway but there is a wide variation on prices from £50 Bosch to £200 Maserati, can anyone recommend any alternatives.
 
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Zep

Moderator
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9,110
The first lambda is the one the ECU uses to operate in closed loop, in that it is a measure of the fuel mixture. The secondary one is there to determine the correct function of the cats.

There are a few threads on alternative lambdas. Have a rummage in the alternative parts thread.
 

jasst

Member
Messages
2,313
Final thought, on the standard version there are 2 cats and 2 lambdas one before the first cat (182837)and one after (191412)which are different part numbers. What’s the difference?
on the larinis there is only one cat at the rear with one lambda at the front end, which lambda should be used front or rear and could this be causing the problem. I think I’ll invest in two new lambdas anyway but there is a wide variation on prices from £50 Bosch to £200 Maserati, can anyone recommend any alternatives.
The difference is in the length of the cables for one, the front ones won't fit on the back because the cables are not long enough. Bosch Lambdas are fine think the oem are actually Bosch, I fitted 4 new Bosch ones to mine and even the writing looked the same as on the ones that came out.
 

3hcp

Member
Messages
238
Thanks for that.
question is if there were 2 lambdas on the original cats and 1 one the larinis which do I use front or back or is that the problem?
 

Zep

Moderator
Messages
9,110
There are four bosses for lambdas on the Larini pipes too, two pre cat and two post cat.

X marks the spot(s).

1695145790734.png
 

3hcp

Member
Messages
238
So today I fitted 2 new rear lambdas and extenders which I stuffed lightly with wire wool as per a previous recommendation. Quick blast around the block and all seems ok, I’ll give it a proper test next weekend and report back.