Reduced/low boost - not DV tear - advice required

[reidy-]

Hi,

So I've noticed recently a drop in power in my GTI and its been getting progressively worse, its always been fairly intermittant but now seems to be more often present than not

I removed the diverted valve yesterday (Rev C @ 99k miles & 250bhp)  inspected the diaphragm and its totally fine which was a big surprise given its revision and age!?
I'd preemptively ordered the rev D expecting this to be the problem which I will probably fit anyway just to be thorough.

PCV valve was changed for new about 1k miles ago after it failed - of note these low power issues started showing up a few hundred miles after this was fitted - (I really hope that its just coincidence)


Typical symptoms will be no/low boost from 750-2500 RPM then it kicks in a bit at 2500 and is flat/consistent middling power to redline

occasionally though it feels like there is no boost at all across the entire rev range

and every now and then I'll put my foot down and it feels about right... maybe 90% of full power (by feel only)



My reasoning points towards a faulty/failing turbo actuator, but I'm just not sure any other suggestions/diag's would be great- I do have a VCDS reader if critical, but would need to buy a laptop to use it in the car so not massively keen on grabbing one of those for a one off data log.

thanks in avdance
Reidy-

[reidy-]

FWIW the car has just thrown a code P0642, but the boost seems to have improved since removing and refitting the diverter valve...

I'll keep plodding along and update if anything changes...

[Newbieintown]

Hi my friend on his GTI had the same issue, his turned out to be his cat was partly blocked.

[reidy-]

Hi my friend on his GTI had the same issue, his turned out to be his cat was partly blocked.

It's a possibility I hadn't considered, but I'd expect MPG to go through the floor if that was the case?

if anything its better than it ever has been, getting me 41.5mpg average on a 200mile run (100 out and back)

[Dan_FR]

The car needs data logging, as a loss of power could be caused by a number of things. Can you not simply borrow a laptop, of find someone local who has VCDS? Or find a second hand windows tablet, like the Lynx 1010 for example, which will run VCDS

[f00glee]

I suffered from a blocked cat after a pre cat removal. My MPG didn't suffer, just power was down. R-Tech confirmed car down to 180BHP  from 250. They diagnosed as either N75 or exhaust. Tried N75 - no different, then a swapped OEM downpipe later and I was back to full power.

Along the way there were some red herrings, did some boost logs and wasn't boosting any higher than ~11PSI whereas normal is around 21. I instantly thought it was a boost leak but ultimately turned out to be the exhaust restriction not allowing the engine to breather properly.

Unfortunately, if it is the exhaust you can only test it by swapping it out.

[reidy-]

Thanks for the input gents

I'll have a look into grabbing an ebay special then and hooking up my VCDS

I'm going to see if its the MAP sensor first though as they're only a few quid, and it would explain all the symptoms and the new error code all in one....

will keep you posted once I get a data log sorted


thanks