All Things Mk5 > How to Guides / Troubleshooting

Possible boost fault???

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Tom_such:
Hi guys, my first post on the forum. Always followed and read but never felt the need to post as of yet!!!

Not sure if I've got a boost problem.

I've recently fitted a boost gauge so that's why I'm worrying. Never noticed anything before (as I couldn't see what boost I was running).

Basically in 3rd gear I can be on WOT and max boost goes up to 11 psi but by about 4500rpm it drops off to 5 psi!!! Is that too much of a drop off?

I've got no fault codes

I'm hoping to book in for a re-map at Rtech in a couple of months and wanna make sure everything is spot on.

Hope someone can help. 

Spec is 2006 gti Ko3

Forge twin take
Forge DV
De-cat

cooljimy84:
What about in another gear ? And does it peak back if u come off the loud peddle and then back on again ?

Tom_such:
It's the same in every gear.

If I let off then put my foot down the same happens again, up to 11 then down to 5psi.

Could it be because of my de-cat but not had it mapped yet? Could that upset the fueling/boost???

cooljimy84:
Not sure, is it the main cat or the one next to the turbo ?

My first through would be boost leak, as it's spiking, but then dropping right down, like a leak only when on boost. Do you have access to vagcom ? or a scanner tool ? might be worth looking at the fuel trim if u suspect under/over fuelling. Also check for 'soft' errors, i had a knock sensor feeding bad data which was making my engine pull my timings right back...

Tom_such:
Both cats are gone! :smiley:

I will check more on the scanner at work.

It does sound like a boost leak under load, will have to check a few other things.

Only fault code I've had recently is cat efficiency below threshold because of the de-cat!!

Thanks a lot for your help though!  :happy2: hopefully I'll get it sorted!

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