MK5 Golf GTI

All Things Mk5 => How to Guides / Troubleshooting => Topic started by: Tom_such on January 25, 2015, 06:56:33 pm

Title: Possible boost fault???
Post by: Tom_such on January 25, 2015, 06:56:33 pm

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

Title: Re: Possible boost fault???
Post by: cooljimy84 on January 25, 2015, 10:11:38 pm

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

Title: Re: Possible boost fault???
Post by: Tom_such on January 26, 2015, 05:42:48 pm

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???

Title: Re: Possible boost fault???
Post by: cooljimy84 on January 26, 2015, 09:10:07 pm

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...

Title: Re: Possible boost fault???
Post by: Tom_such on January 26, 2015, 09:43:33 pm

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!

Title: Re: Possible boost fault???
Post by: jhook661 on February 07, 2015, 05:34:02 pm

Did you find the fault as I have a similar problem boosting to 11psi then dropping off straight after ? To 4-5psi ?

Title: Re: Possible boost fault???
Post by: Tom_such on February 10, 2015, 07:32:30 am

Hi, no haven't found the fault yet.

I'm still looking into it, gonna check the N75 valve and then get a smoke tester to check for boost leaks.

Let me know if you sort yours  :happy2:

Cheers