Major power loss in 3rd and above!

[Kiel_GTI]

Hey guys,

Got a problem with the polo, im apr'd and have SEAT, BMC and a FMIC. In 3rd gear and 4th and 5th when i put the foot down at about 3000rpm it starts boosting real hard, but then i get this cut out of power, then the hard acceleration then a cut out again.

Its quite annoying as it makes the car feel very slow, anyone know how i can get that linear power delivery that doesnt cut out? It sounds like the turbo stops sucking the air in when it stops charging hard. then comes back in.

Kiel

[Jmac]

Faulty N75 or wiring making and breaking on the N75. Seen a few. Faulty DV too mate.
Good luck
Jmac

[noone]

I'd start with the N75.

I have a J version floating around if you are interested.

[Plautos]

I had this problem once, just after I had installed a bigger downpipe.

I had a first stage ECU tune, boosting 1,3bar.

With the new downpipe the boost reaches 1,6bar. These cuts and goes start to happen at 3000rpm, stopping above 5000rpm.

I solve the problem with a new ECU re-flash.

[noone]

Oh, just noticed you are running MBC! Is this bypassing your N75 or in parrallel?

1.3, 1.6? damn, I'm lucky to clip much over 1 bar.

I spike to 1.2 occasionally. Don't think I want to go down the MBC path...

[Kiel_GTI]

thanks for the responses guys.

So i have done some reading and essentially you think it is the N75 opening the wastegate prematurely because of the excess boost, and a N75J is designed to hold that boost to the wastegate better?

Kiel

[noone]

I was hoping someone else might have posted first as I'm not as educated on these issues.

IMO, the N75 is either being told to do too much, or the ECU is freaking out because the changes it expects to see when it turns the N75 on and off are not happening.

First step, remove MBC.
If this does not fix it, try a new N75.

Alternately, you may want to check for codes or reset eeprom (remove battery power for 20 min).

[Kiel_GTI]

Um, what is the MBC?

[noone]

Oh sorry, BMC, not MBC!

I thought you were running a Mechanical Boost Controller (ie bypassing the N75 or running in parrallel).

[break]

Oh, just noticed you are running MBC! Is this bypassing your N75 or in parrallel?

1.3, 1.6? damn, I'm lucky to clip much over 1 bar.

I spike to 1.2 occasionally. Don't think I want to go down the MBC path...

Isn't that fairly low boost for a flashed Polo? Most I see are running 18psi minimum (1.2 bar). Mine (and a few others I've seen) is running 20psi - 21.5psi peak (1.37 to 1.48bar).

[noone]

My understanding of the K03s is that its efficiency range starts to trail off after about 16 psi. Of course you can run the turbo a lot harder, I'm not going to touch on what happens with higher boost in terms of gained power, added heat, power lost to pushing the turbo beyond efficiency range, so many theories and ideas on this. Was reading a thread today where someone was spiking 29 psi, but only holding 15...

I'm not sure how a boost gauge compares to logging with vag-com, would be very happy to see some logs that others have done so I can compare.

Could have something to do with my tune and mods.
I'm running APR stage 1, V2. APR is not known to be an overly agressive tune.
As I have improved the intake, dump, TIP, etc I think the flow of air is working better. Hard to explain, but a notion that air movement being more than just how much pressure there is.

Too many factors IMO, I'm not fussed about what my tune is doing specifically with the boost for now as I've been getting great results with advancing the timing. A few PSI more or less does not seem to have nearly the same impact as a few degrees of added ignition timing.