Removed precat now getting fuel cuts?

[Mk5_Jim]

Hi guys so yesterday I removed my precat, all went well and took us 2 hours thanks to a very stubborn exhaust rubber!

Took it for the initial test drive and it felt no different really - maybe marginally louder. However after 15 minutes driving it started to feel odd. Under high load it would accelerate very slowly and it felt like it was cutting fuel. After another 10 minutes my CEL flashed a few times  and went out so I pulled over and switched off for 10 minutes, turned it back on and no CEL after another 5 minutes the CEL was back but this time just on constantly (not flashing). The car feels fine under normal loads but anything above 4k and it just stops pulling?

Initially thinking maybe a worn cam follower and just coincidence in the timing of it or that I have damaged a lambda sensor. The first lambda right by the turbo was left on while we knocked the precat out as it was proving very tough to remove however I took care not to hit it or lean the chisel on it! Could the precat dust have got itself into the sensor?

The car is a 2007 57 GTi DSG with 67k on the clock and no other modifications. Any help would be greatly appreciated!

[Mk5_Jim]

The problem seems to get worse the nearer the redline you get, I've stopped trying to provoke it and am now driving it like a nun until I can get this sorted   

[Shaw]

Seen this talked about a few times after a pre cat removal.

When you removed the pre cat did you also make sure you removed the fiberglass/asbestos looking stuff that was stuck to the inner wall of the pre cat housing?

Sounds like a blocked main cat possibly?


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[GrayMK5GTI]

I've never heard this talked about after pre-cat removal? (at least not on this forum)

I think you need to scan for fault codes, it sounds like you may have damaged the lamdba sensor tbh 

Its like fitting a performance down-pipe, you shouldnt get fuel cuts as a result of it.

[Mk5_Jim]

Thanks for the replies, I made sure that I removed everything to do with the precat so don't think it could be a clogged cat. Starting to lean toward a damaged lambda due to dirt getting into it? I only suggested fuel cuts being the issue as the dsg fart between gear changes has also disappeared and under light acceleration the car picks up as it used to its only when using medium to full throttle that the lack of power is properly noticeable. I'm going to take off the MAF and see if it runs better or worse. Also might try disconnecting the battery for 15 minutes as some people have suggested this may help? Anyone know how much an indy is likely to charge me to just run a scan?

[xjay1337]

Have you scanned it to see what the fault is?
Could very well be coilpacks or did you knock the lambda sensor...??

[Mk5_Jim]

Haven't had a chance yet. The car idles smoothly and doesn't feel lumpy, wouldn't coil packs do this?

I was very careful to avoid the lambda and definitely didn't hit it with the chisel but when getting my hands in there to remove the precat material I may well have bumped it with my hand?

[xjay1337]

Haven't had a chance yet. The car idles smoothly and doesn't feel lumpy, wouldn't coil packs do this?

I was very careful to avoid the lambda and definitely didn't hit it with the chisel but when getting my hands in there to remove the precat material I may well have bumped it with my hand?

You didn't take the lambda out to hit out the material??

[Mk5_Jim]

Nope, seems stupid now I know. It was too tight to get off without the use of a blowtorch which we didn't have to hand, we just unplugged it and did my best to avoid disturbing it

[GTI-Ross]

Nope, seems stupid now I know. It was too tight to get off without the use of a blowtorch which we didn't have to hand, we just unplugged it and did my best to avoid disturbing it

these sensor are very sensitive (mind the pun) but Yes, there is a very good chance you have damaged it as they are so delicate, even if you have got some dust or particles in it, it can cause loads of problems

[Mk5_Jim]

Ehhh  live and learn though ay! I'll get it scanned when I finish work tonight to double check, is it worth removing it myself and giving it a clean up with some WD40 and seeing if it makes a difference or is it more than likely going to be knackered? Thanks for all of the replies!

[GTI-Ross]

Yeah scan it first, give it a quick clean (i cant 100% confirm WD40, but would think its ok), maybe use an air line / blower if you have one, if not may have to buy a new one.

[xjay1337]

If you've knocked the Lambda sensor (which is what I suspect) you will need a replacement as it would be broken.
VCDS it first to be sure.

Mine came out with a spanner , it stuck in quite a way so no way of doing it without taking the Lambda out imo.

[Mk5_Jim]

I'll let you know what the scan shows and if the clean helps at all.

Jay, it does sit quite far in but you can get around it without having to knock the sensor, the hardest it will have been knocked is potentially with the back of my hand as I pulled some of the precat stuff out. Obviously it's not a good idea to leave it in but as usual being too keen to get the job done quickly has resulted in it needing to be done twice and potentially at some cost to myself haha 

[56OctyVRS]

Lamda sensors are very delicate things and even over tightening them can  cause them to break. They are sensitive to knocks and vibrations so there is a chance it has fractured the sensor on the inside. Hope you get it sorted soon