WG spring opening pressure changed

[adam g]

Can anyone shed any light on the following.

I got with a job lot of spares quite a stiff waste gate spring that I tried in place of the stock one about 6 months ago, prior to my car being mapped. With the N75 off (pushing all pressure to WG) the spring pressure was circa 21.5 psi hence I believed it to be a 1.5 bar spring.

I put a lower rated spring back in when I took it to be mapped in case I had surge and needed a lower opening pressure. However, one mapped I had no surge and the boost is always set above 22 psi so I thought I could put the big spring back in, mainly to try and dampen some boost oscillation I was seeing.

The weird thing is, with the big spring back in I started again with the N75 switched off and the boost shot up to 35 psi and blew the end off the intercooler.

Surely a 1.5 bar spring is a 1.5 bar spring independent of the engine mapping. As I had the boost map off in both cases the only thing that had changed was the timing and fuel map.

[Rusty]

Boost is a combination of N75 duty cycle and spring pressure, so once mapped, you cannot swap springs without getting the map tweaked.

Your boost spike has been caused by a disconnected WG hose. No hose = max boost. Connect the WG to the inlet manifold and I'll be back to normal.

What you're proposing is not a good idea though.

[newsh]

The ECU can only give you more boost than spring pressure not less.

If the WGFV was unplugged and you're still running the same turbo then you should have got about the same boost as last time you tried that spring. Perhaps when you assembled the WG cap the spring didn't seat properly on the perch and the WG is not opening at all?

I presume the WGFV is all plumbed in correctly?

[Rusty]

As I said, plumbing.

The boost pushes AGAINST the spring to open the WG, so it's a fail unsafe system. With no boost going to the WG, even the stock spring would give 2 bar boost!

[newsh]

He doesn't say he removed the pipe though, he says unplugged so I would think disconnected electrically

[Rusty]

Me too but the symptoms are those of plumbing or broken diaphragm. One option; s that the N75 has seized shut or is blocked.

[newsh]

Yep

[adam g]

I haven't touched the plumbing, I had just switched the N75 off via the ECU (I have stand-alone) to give what should be spring pressure.

Okay, so we agree it cant be the timing map change that's caused it.

Thanks for suggestions. i'll check if WG spring is seated properly and not jammed somehow. I guess the best way to check for N75 operation is to by-pass it and connect the turbo outlet straight to the WG.

[Rusty]

Yes, bypassing the N75 is a good test. Also see if the diaphragm can hold a vacuum.