50/50 Performance...

[SvtAlex]

I have a strange issue with my 03 cobra.
About 50% of the time the boost only goes up to about half of what it's supposed to, and the car seems to sound more muffled when it acts up.
The only mods I have are; a pulley, intake & exhaust.
Changed sparkplugs / oilfilter / oil / cleaned airfilter last winter.
I have the Diablosport Predator that I got with the car, so I'm going to try and do some datalogging to see if anything stands out.
Other than that, I'm not quite sure where to start looking!!
By the way, I have the "P0455" evap leak code and fuel cap light if that could have anything to do with it.

Anyone heard of a similar problem or have any ideas?

 

[WHITESTRIPES]

Did you ever get it figured out? Sounds almost like a bad bypass valve.

 

[SvtAlex]

Thanks for the reply. I havent figured it out yet. I'll have to check the bypass valve.

 

[SvtAlex]

I did some looking into my bypass valve and it turned out that my lower vacuum line was blocked off, when it is supposed to go to ambient pressure? I removed the cap and had no issues on a short test drive. I will have to drive some more to be sure, but it's looking good so far! Fingers crossed.

 

[SvtAlex]

SOLVED! Thank you Whitestripes!

Okey so as I wrote earlier, it turns out that the lower vacuum hose from the Bypass Valve was completely blocked off by being "connected" to this here(1st pic). And this threw me: P0455, P0457 & the "Check Fuel Cap" light. I unplugged the vacuum line to ambient pressure, took several test drives, and It's all back to normal with no error codes!
After looking at Mark Olsons' Vacuum Harness Diagram I can see how someone could have made the error, seeing the resemblance from the diagram to where it was actually plugged in.