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Discussion Starter · #1 · (Edited)
Basically I have an Evo X FQ300 SST decatted with new elbow and Miltek 3" exhaust, remapped to 360bhp.

I have fitted an elbow with small inlet on the exhaust for the 2nd Lambda sensor to reduce the gas flow to the sensor to prevent the engine light coming on.

In general this works very well but something strange has started happening in cold weather. I drive over the mountain road up to a height of about 2000' 3-4 times per week to go to work. When the weather is cold the engine light comes on at the same stretch of road each time, sometimes it goes into limp mode telling me I need the car servicing, other times it continues to run fine.,

When it goes into limp mode I pull over, switch off the ignition, leave for abouit 30 secs, restart the car and the engine light is still on but the car drives fine.

After a couple of days of driving the engine light goes out. Also had the fault code checked a couple of times and always the same saying the cat isn't working properly.

It can happen in either direction at two different stretches of road but both are roughly the same height and just before I reach the highest point.

Obviously something to do with air pressure and temperature but what can I do to prevent this from happening apart from fitting a Cat again ??
 

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Sounds like exceeding airflow limits or triggering overboost, as you say, possiblly relating to change in altitude...(is this same section of road going uphill at all?) A map tweak would fix it (if this is the issue)... The X can be mapped for barometric pressure so this can be avoided, very popular in the states where there can be bigger altitude variations.
Best to go to your mapper and get the error codes checked before trying any fixes, and drive gentle in the area you find triggers the code until then.

Has anything been changed since the car was mapped?
 

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Discussion Starter · #3 ·
Sounds like exceeding airflow limits or triggering overboost, as you say, possiblly relating to change in altitude...(is this same section of road going uphill at all?) A map tweak would fix it (if this is the issue)... The X can be mapped for barometric pressure so this can be avoided, very popular in the states where there can be bigger altitude variations.
Best to go to your mapper and get the error codes checked before trying any fixes, and drive gentle in the area you find triggers the code until then.

Has anything been changed since the car was mapped?
Yep going uphill slightly in both directions. Problem is I live in the Isle of Man and nobody over here who can map, have to bring someone in from England. Guess I'll just have to wait until the next rally and they bring a mapper over.
 

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Wrc cars have a cut in power like this too lack of oxygen in the air as said before ecu thinks the air pressure & oxygen levels are the same as when it was built so I doesn't realise it's at 2000' if you mapped it at this hight then it will run different again at sea level
 

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Discussion Starter · #5 ·
Wrc cars have a cut in power like this too lack of oxygen in the air as said before ecu thinks the air pressure & oxygen levels are the same as when it was built so I doesn't realise it's at 2000' if you mapped it at this hight then it will run different again at sea level
So is it happening because of the decat or is it the way it's been mapped and how do I fix it ? Do I need to get the map changed or do I have to replace the Cat ?
 

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Get a Diagnostics logger and record the logs on the drive. At least that way you can post the logs and someone can help with spotting a fault just before the car goes into limp mode
 

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Discussion Starter · #7 ·
Get a Diagnostics logger and record the logs on the drive. At least that way you can post the logs and someone can help with spotting a fault just before the car goes into limp mode
Way over my head, wouldn't have a clue where to start and gussing it will be expensive ?
 

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Has anything been changed after the original map?
This would happen to a normal X if a decat was fitted without being remapped. If you put the cat on, it will probably stop the cel but it isn't the proper fix
Having the elbow for the O2 sensor will stop a cel light. You really need to get the codes from the obd2. Without knowing what the error codes are you can't get accurate advice.
It could be because of the map or the decat or both, or something different altogether.
 
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