Hello all,

I've successfully upped the fuelling on my car, and now I seem to have a problem with my boost. It peaks at just under 15 psi, and then drops to about 10-11 psi, in every gear. My wastegate is locked, and I'm running very safe AFRs, about 11:1. I'm wondering if it has anything to do with either

1. My throttle partially closing past a certain rpm/boost/load condition

2. Some issue with my turbocharger

For reference, I'm running a TD05 16G with an FMIC and a standalone engine management system. The EMS has its own MAP sensor, and I've unplugged the OE MAF that sits on the intake. The DV is also left to vent open. The turbo's wastegate is locked, and it should theoretically boost till a maximum of about 22 psi, which is what I want.

Has anyone else had this issue? Is there some sort of fix or workaround to this?

TIA and cheers!

Edited 2 December, 200916 yr by parasight

"a standalone EMS" - well, I don't know if we can help then, because we don't know what you're running, but the stock EMS will monitor and control boost levels.

Oh well, it's an EMS that only controls fuelling and ignition. All other functions/ancillaries are controlled by the OE ECU, which is why I was wondering if it's some sort of limp mode response.

Also, I've disconnected all the lines to and from the N75 valve, so the ECU shouldn't be able to control boost (atleast via the valve). I'm not sure whether this was a good idea, or very stupid.

Ah, trying to disconnect the N75 like you've done is a very bad idea. In fact, unless you install a full EMS that replaces all the standard unit functionality, I think you'd need to remap the standard unit to run higher boost, at which point you could change the ignition and fuel maps too.

There's no way to run an EMS just for fuel/ignition and disregard boost levels on the OE sensors and ECU? Maybe run a bleed line off the N75?

Well, not that I know of; most people just remap the stock EMS rather than fitting a piggyback. I think you need a specialist who knows VAG cars, and your piggyback.

You might try Unit18 in the Site Sponsors section, because Ally there runs a modded Nissan Silvia as his personal car, and piggyback systems are more common in Jap tuning.

Well if you've locked the wastegate closed (just pull the hose off the actuator to do this), and the N75 isn't connected anymore..... you're essentially running a non-wastegated turbo. So you run the very real risk of overspeeding the turbo at high revs or altitude. Anyway.....

I'd say that the N249 is opening the DV, and dumping off boost to bring it down to the stock 10psi. If it's not that, then the fuelling is being automatically reduced by something. Basically something is putting out an over-boost signal. Try bypassing the N249, and run a vac hose straight from the inlet manifold to the DV.

What EMS you running?

I think, though I'm not entirely sure, that this leak/drop issue exists even with the standalone disconnected, and the car running OE maps, with a larger turbo. Gotta clean all codes and check once.

Well if you've locked the wastegate closed (just pull the hose off the actuator to do this), and the N75 isn't connected anymore..... you're essentially running a non-wastegated turbo. So you run the very real risk of overspeeding the turbo at high revs or altitude. Anyway.....

Yup, I'm willing to go with that.

I'd say that the N249 is opening the DV, and dumping off boost to bring it down to the stock 10psi. If it's not that, then the fuelling is being automatically reduced by something. Basically something is putting out an over-boost signal. Try bypassing the N249, and run a vac hose straight from the inlet manifold to the DV.

What EMS you running?

It was doing this, so around 5500 rpm, when it hit 1 bar, it would open the DV (pretty loud since it vents out now) and I could hear it even on full throttle. So I've now routed the DV straight to the intake manifold, using the same vacuum source as the FPR. That solved the DV opening, but unfortunately the boost still drops. Which is what leads me to believe it's the throttle plate, or the turbo itself somehow. Logically, only these 2 parts can still alter or control boost.

This is the EMS I'm running. Not sure about Briskoda's marketing/commercial interest rules, so please forgive me if I've goofed up. http://racedynamics.in/

Reading your last, are you running an atmospheric DV? If so, change it back to a recirc type, because the VAG EMS doesn't like atmo DVs.

No issues about saying "I'm using this aftermarket part" unless you happen to own the company!

For info, the OP is located in India so there is little point in mentioning popping to a UK tuner for a custom map or other details.

If you bypass the wastegate on the turbo and then bypass the N249/DV the ECU can alter the throttle as a last resort to try and maintain control of the engine. That is why mapping of the stock ECU works well as they can adjust the parameters for the wastegate opening, fueling, DV and throttle etc. Try a search on vwvortex as there are a few guys on there running alternative engine management systems.