4Driver4

Update on my crazy high boost issue:

First off, thanks for all the ideas, and thanks to an unnamed lister for the unsolicited loan of a known good MAF and another lister for a WG loan.

At this point, in addition to the things I tried in the original email, I've also changed the MAF and WG with no improvement, and I've done some monitoring of the WGFV activity. Currently I have T'ed a boost gauge into the line running from the WGFV to the WG so I can see when boost is being routed to the chamber to open the WG. I've also tapped a dwell meter into the wires feeding the WGFV so I can see when it is receiving a signal. I've installed a normally closed pushbutton switch in series with the WGFV, allowing me to cut power the switch, route boost to the WG and thus knock boost back to 7 psi at the push of a button. Both the meter and gauge are taped to the outside of the windshield, giving the green monster a very slick ricer look. Cops dig it.

Everything seems to point to the ECU calling for this high boost. The WGFV receives a signal (causing boost to rise) even when boost is at 31.5 psi. Depress the pushbutton and dwell falls to zero (duh - no power) and the boost gauge shows pressure immediately routed to the WG , causing the WG to open and boost to fall. On the highway in higher gears under load, boost is at 31+, and the WGFV is still receiving a signal from the ECU causing it to stay open and allow overall boost to build.

In summary, my testing show that the WGFV, assorted plumbing, and the WG are all working as designed, but the ECU demands more boost.

Help.

Tom

Original email from S-car list:

I have a strange problem with my 95.5, and I can't seem to get to the bottom of it. The car will overboost to 30+ psi in fourth and fifth gears. I assume it would do the same in the lower gears, but it accelerates fast enough so that pressure is unable to build to these levels.

Some background: The car has 82k on the clock, RS2 EM and turbo, Stromung, 34 lb/hr racetronics injectors, stock MAF, Hyperboost BPV, and Mihnea's custom tuning. Wastegate spring is at the factory setting. There are no boost leaks or ingition problems. Since Marc S is running a nearly identical set-up (034efi turbo and stock exhaust are the only differences), I have been swapping parts back and forth between our two cars, attempting to isolate the issue. Marc's car runs about 26 psi.

So far I have:
Reverted back to Minhea's "off the shelf" standard chipset for the RS2/34# combination
Swapped ECU's
Swapped the altitude sensor
Installed a new WGFV
Unplugged the electrical portion of the WGFV and observed 7 psi max boost
Swapped the wastegate

Since I just recently started running an installed boost gauge, I have no idea how long this problem has existed. I suspect it was there even last year when Mihnea tuned the car. Before we went out, he had he uncap and crank the WG down 3 turns, but after the tuning he told he to crank it back out 2 turns.

I'm running out of ideas. Anyone?

spiralsmurf

to limit the max boost. or get an electronic boost controller

Julian_B

he tried that already

4Driver4

Hoping that either one would be able to limit boost. Results were not great, but I didn't spend the time I should have fine tuning it.

I've been swapping parts with Marc S, but his turbo is different than mine, so I'd really like to swap my ECU into an identically equipped car and see what happens.

VR_Life

You could try swapping the N75 WG Controller, that can be an issue, but ...

On the B5 the N75 WG controller is just very slow at applying control to manage fast spikes. Software typically has to guess where the boost is going and apply an expected duty cycle because it takes too long (at least 100's of ms) for the servo magnet to start changing duty cyce in response to closed-loop control.

The only solution is to switch to electronic (e.g. APEXI AVC-R) or manual boost controller (e.g. Forge). Many Stage 3- folks run the EBC/MBC in parallel to the N75 to retain ECU control of boost and just keep a cap on spikes. STFA on B5 S4 for diagrams.

4Driver4

This is the car pulling like hell at 31.6 psi with the ECU sending a signal to the N75 WGFV to devert control pressure away from the WG. In other words, even though the car is overboosting for several seconds, the ECU demands more boost. Something is broken.

a4kquattro

We need to hookup the LED setup to my WGFV to verify whether or not my setup is open or closed at peak boost. For all we know my turbo could be topping out at 26psi. Only one way to find out...

kday

That's interesting because it's outside the range of a 3 bar map sensor at sea level. (3 bar absolute = atmospheric + ~28 PSI). If your TDS-1 is reading 31.6 then I don't think it has measured atmospheric pressure properly, or it's configured for the wrong MAP curve. What have you seen on the analog boost gauge?

Can you adjust your VMAP to e.g. 3.2 bar?

4Driver4

The analog boost gauge shows the same.

kday

implies that the transducer is essentially maxed out. The transducer has a 0-5 volt signal, and 5 volts is 32 PSIG at standard atmospheric pressure (+/- depending on the actual atmospheric value read). This is beyond 3 bar absolute...

Does your analog gauge go beyond 30 PSIG? If not, then you may actually be going beyond 31.6, since that is right about where the TDS-1 will be "pegged" with a 3 bar transducer.