UrS4 VEMS Questions...

[Auditude2.2T]

So after a few reoccurring stupid issues I finally got my car running and driving pretty good...


Just emailed Marc and hopefully he can fit me in the first week of December to get Da Fridge tuned..

However before I make the trip over to EFI I have been trying for months to just get the car mechanically sound so we don't run into any issues while tuning. Here's a list of things I've done and maybe someone can point me in the right direction..

I had the head rebuild do to a valve problem, while doing this i also got a new CPS Sensor since they are known to go bad. After re-installing the head I had a few issues but I had a friend and fellow forum member AMDISTHEBEST come down to me and give me a hand fine tuning the car. It was a disastrous night bc of a bunch of stupid issues on my part but Nick stuck it through with me and the car was running really good and felt great besides the slipping clutch, lol... So now I got a Tilton Twin Disc Setup with the 034 Flywheel. I also changed the wastegate to vent to atmosphere and vbanded the downpipe to the catback. I'm not sure if it was imediatetly after this but at some point the car decided to stop making boost. It hits around 5psi in 1st and made 7psi tops in 2nd and just is dead. The car idles fine, runs good normal driving, AFR look good etc.. I pressure tested the car and found a crack in the Apikol Intake Manifold and a few leaks by the injector seats so I took off the intake, replaced it with my OEM AAN Intake that I had powdercoated from my old car and fixed all the boost leaks I could find. Still the boost issue is continuing. So then I tried changing the N75, issue still here. So I took off the wastegate and checked if there was anything wrong internally.. Everything was fine...


So now I'm stumped. To my knowledge everything is hooked up correctly, there are no major boost leaks, I'm getting a reading from everything on VEMS and everything seems like it should be where it should be..

Any one have any ideas??

[chaloux]

A log would help immensely here. At least to verify everything that VEMS is seeing is normal. Seems like spring pressure but that depends on your spring setup in the WG.

[chaloux]

And that sucks about the Apikol... You going to fix it?

[Auditude2.2T]

And that sucks about the Apikol... You going to fix it?

Just going to have it repaired and throw it on when I end up doing Pistons and going really apeshit. Only going for a reliable 550whp on E85 for now. Shouldn't be too much of a problem especially with Marc tuning.

[Auditude2.2T]

A log would help immensely here. At least to verify everything that VEMS is seeing is normal. Seems like spring pressure but that depends on your spring setup in the WG.

I'll get some logs today...

Wastegate seems fine, I took it apart and even tested it and it seemed all good. Going to maybe replace the N75 with a MBC today.. Thoughts?

[loxxrider]

I bet the wastegate spring is much more than 5-7 psi in that car. Ed was not dumb enough to try and run 35psi on a 5 psi spring. The spring should be at least 14 psi. You either have a leak or the turbo is not spooling (physical blockage). Does it spin smoothly?

[chaloux]

That was my next question, is the turbo actually spinning?

[Auditude2.2T]

I bet the wastegate spring is much more than 5-7 psi in that car. Ed was not dumb enough to try and run 35psi on a 5 psi spring. The spring should be at least 14 psi. You either have a leak or the turbo is not spooling (physical blockage). Does it spin smoothly?

Yeah it's spinning freely. I took the intake off and watched it.

[roortube]

Try to wobble the shaft whwn the engine is off. Sometimes a bad bearimg will work ok with constant inout, like idle, but freak out with changing input.

Also check the signal line to the BOV...a small leak there can dump lots of boost in a hurry.

[EDIGREG]

Upload your current config. And post a photo of how you have the wastegate plumbed. For the love of god do not install a MBC, diagnose the issue.

The N75 is a pressure reduction valve. Full boost pressure is provided to the lower wastegate chamber, which opens the wastegate (N75 0% DC or electrical connector unplugged). When it pulses, the N75 valve opens and the boost reference is dumped to atmosphere (or back into the intake in a stock MAF configuration).

Double check the N75 plumbing. One leg goes to the compressor housing, one goes to the lower wastegate chamber, and the 3rd is vented to atmosphere.

In order to troubleshoot, you can remove the n75 valve from the equation entirely by disconnecting the boost reference line to the lower wastegate chamber...this will give you maximum mechanical boost. MAKE SURE YOU HAVE BOOST CUT PROPERLY CONFIGURED IN ORDER TO PREVENT OVERBOOST. Set it low, I would start at 15psi. If you still do not get any boost, then you have a major boost leak. As mentioned, make sure the BOV is not opening.

If you are not comfortable, leave it alone and let Marc fix it.