GTM stage 1 S/C - Throttle not opening fully? Or boost leak? Please help!
 

So more than 2 years after installing a GTM stage 1 S/C, I still am plagued by gremlins.

Basically, cold start performance is excellent. I get on-boost instantly and it pulls like a maniac. After it is fully warmed up, I get consistently poor (slower than stock) performance, with intermittent full-power.

I have spent days and days chasing boost leaks that simply don't appear to be there. Everything is double-hose-clamped and holds 15psi on a pressure test with no leaks to be found...

I've attached some screenshots of uprev logs showing two runs in second gear, performed about 15 seconds apart. In run 1 (good run), which is ~2800 to 4000 RPM, I instantly get boost, which rapidly builds to ~5psi by 4000rpm. Power delivery is excellent, timing advance sits at about 15 degrees during WOT and the throttle & VVEL exactly match my accelerator input.

The second run, performed literally 10 seconds later, with WOT from ~2800 to 4000rpm, exactly as in the good run. The car sits at 0psi, then builds to maybe 1psi by 4000rpm. Performance is horrific. Timing sits at ~22 degrees, and the throttle and VVEL seem to slowly work their way open rather than matching the accelerator pedal input.

I have played with the throttle maps for hours, and I simply don't understand how WOT at the same RPM, in the same gear, performed 10 seconds later, can have a completely different response! I assume if this was an (impossible to find) boost leak I would get the VVEL & Throttle performing the same way in both runs?

It's like there is some other feature/sensor/something that is wildly changing the car's throttle response, even on identical runs.

I'm so sick of battling this gremlin, and it is really sapping any fun out of the car :( Any advice would be greatly, GREATLY appreciated!!!!!

Thanks :)

That doesn't sound like much fun... I'm no expert but could it be something with the intake manifold? Have you reached out to GTM?

This isn't a piping boost leak or it wouldn't be sporadic. First thing I would do is clean and inspect your bpv. Sounds like it might be getting stuck and allowing boost through it.

BPV is a good suggestion. What about throttle position sensor?

Would this also cause the PCM to play games with the throttle, etc due to AF ratio?

I've removed, torn-down, cleaned, lubricated & re-assembled the BPV (35mm turbosmart re-circulating). It seems to operate smoothly and normally in response to pressure/vacuum changes. About 6 months ago out of desperation I even replaced the cut-down spring with a full-sized supercharger spring from Turbosmart (which is far too strong for the GTM setup, locking the valve closed most of the time and causing a lot of flutter, but certainly ruling out the BPV recirculating).

I did speak to Sam but then he stopped responding, so I'm battling this one on my own now.

I was also thinking maybe a boost leak where the plastic manifold meets the head, but that doesn't explain why the throttle and timing are so different (I would have thought that, boost leak or no boost leak, the throttle & timing should behave the same). I've removed and reseated the intake manifold at least 4 times over the past couple of years, including replacing the gasket, and it all seems completely fine.

I'm most confused about the throttle and timing differences between the two runs - I just can't understand how or why the ECU is doing what it is doing, especially as the MAF sensor readings are quite similar between the two runs.. It's like there is some unknown third variable the ECU is using to decide how to perform :(

What about the super charger itself? Are you confident the internals are working properly? Hopefully you don't have any valve train issues either. How about reloading the tune? Is there such a thing for the 370z? I did that with my Supercharged Mustang a few times.

Just throwing things out here... Belt slip? :-) I'm guessing it's ok?

PCV valves?

Belt coverage with the GTM kit is very high, the belt is in good condition and tension is fine so I think that can be ruled out. PCV is fine as well, unblocked and no leaks.

Supercharger I'm fairly sure is fine internally, as it has no trouble producing power when the throttle wants to open properly :)

Make sure supercharger traction fluid isn't low ...and when is the last time it was changed...if I remeber correctly our super chargers work with a type of traction drive to engage internally ...

I assume it behaves the same way stationary or moving? Did you say you checked/replaced the throttle position sensor?

On my Mustang I had to turn traction control off completely. It literally stalled the car any time I pushed the throttle just a little aggressively.

Same problem I had it's a bad tune from GTM (sam)

Turn the highlight function to "OFF"

Make this change and all will be well!

http://www.the370z.com/forced-induct...ing-boost.html

http://www.the370z.com/members/pokey...74308-tune.jpg

Damn! I just read that thread. What a nightmare.

ditch uprev and go to ecutek, there are several parameters that are not accessible in uprev that exist in ecutek.