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Discussion Starter #1
Hello all, have a problem with my Giulietta QV. Fitted a new downpipe without a cat. Went on the motorway then all of a sudden engine light and no power. Managed to get it home after being safely guided off the motorway by the RAC. Only code that have come up are the p0300 - p0304 codes for all cylinders misfires at various times. What is the cause of this I know the codes are multiple misfires from different cylinders but I can't work out if it's because of the downpipe I fitted messing with fuelling or just the coils or spark plugs. It may just be coincidental that a day after fitting the catless downpipe it goes wrong. Any help would be greatly appreciated.
 

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Think of it this way:-

Modern cars with all the emissions, fuel efficiency, etc. considerations are on a finely balanced beam with a pivot located in the middle. Upset one side and the other side reacts adversely. You'd have to start re-balancing by moving the pivot, adding or subtracting items. On older car engines, such as that in the 156 GTA, were originally set up without all those devices in even older cars and therefore were balanced, so eliminating them from the 156 did have positive effects, effectively restoring the balance. it just doesn't work that way anymore without re-mapping etc.
 

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As above getting rid of the cat has increased flow through the exhaust,which has in turn caused the ECU to have a wobble as the parameters are not out of spec.
If you are running cat less the ECU needs mapping to accommodate it
 

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I am thinking of decat by hollowing out cat and reinstall with high flow cat farther down stream but now im not sure based on problems this guy is having...keep us posted on how u fix this
 

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If you remove the pipe with the cat, then I believe you remove the 02 sensor. The air fuel ratio will be misaligned in conjunction with the ECU’s programme, as mentioned by Jonny.

Think he’s right, the cars going to need mapping in conjunction with the decat pipe.

Plus swapping back again once MOT time comes around

Sent from my iPhone using Tapatalk
 

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Discussion Starter #10
The downpipe I put in had a place for the o2 sensor and I put a spacer between the pipe and the secondary O2 sensor so it wasn't that. Turns out it was my turbo that gave out. Ordered new internals for it so should be fine once I've reconditioned the turbo. Will definitely be getting a remap once the catless pipe goes back on but for now going to run with the cat back in.
 
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